20个开发人员非常有用的Java功能代码

冷不防 2022-09-29 05:29 191阅读 0赞

1. 把Strings转换成int和把int转换成String

<table style="width: 400px;"> 
 <tbody> 
  <tr> 
   <td> <pre>String a = String.valueOf(2);&nbsp;
//integer to numeric string&nbsp;&nbsp;<br>int i = Integer.parseInt(a); //numeric 
string to an int&nbsp;<p>&nbsp;</p><p>String a = String.valueOf(2);&nbsp;&nbsp; 
//integer to numeric string<br>int i = Integer.parseInt(a); //numeric string to an
int</p></pre> </td> 
  </tr> 
 </tbody> 
</table>

2. 向**Java**文件中添加文本

Updated: Thanks Simone for pointing to exception. I have 
    
    changed the code. 
    BufferedWriter ut = null;  
    try 
    
    {  
    out = new BufferedWriter(new FileWriter(”
    
    filename”, true));  
    out.write(”
    
    aString”);  
    } catch (IOException e) {  
    // error processing code  
    } finally 
    
    {  
    if (out != null) {  
    out.close();  
    }  
    }    
    BufferedWriter ut = null;
    try {
          
    out = new BufferedWriter(new 
    
    FileWriter(”filename”, true));
    out.write(”aString”);
    } catch 
    
    (IOException e) {
          
    // error processing code
    } finally {
          
    if (out 
    
    != null) {
          
    out.close();
    }
    }

3. 获取Java现在正调用的方法名

<table style="width: 400px;"> 
 <tbody> 
  <tr> 
   <td> <pre>&nbsp;<br>String methodName =
Thread.currentThread().getStackTrace()[1].getMethodName();&nbsp;<p>&nbsp;</p><p>String methodName = Thread.currentThread().getStackTrace()[1].getMethodName
();</p></pre> </td> 
  </tr> 
 </tbody> 
</table>

4. 在Java中将String型转换成Date型

<table style="width: 400px;"> 
 <tbody> 
  <tr> 
   <td> <pre>java.util.Date = 
java.text.DateFormat.getDateInstance().parse(date String);&nbsp;<p>&nbsp;</p><p>java.util.Date = java.text.DateFormat.getDateInstance().parse(date 
String);or&nbsp;<br>SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" 
);&nbsp;&nbsp;<br>Date date = format.parse( myString );&nbsp;<br>SimpleDateFormat format = new SimpleDateFormat( "dd.MM.yyyy" );<br>Date date
= format.parse( myString );</p></pre> </td> 
  </tr> 
 </tbody> 
</table>

5. 通过Java JDBC链接**Oracle**数据库

public class OracleJdbcTest  
    {  
    String driverClass = 
    
    "oracle.jdbc.driver.OracleDriver";  
    
    Connection con;  
    
    public void init
    
    (FileInputStream fs) throws ClassNotFoundException,   SQLException, FileNotFoundException, IOException  
    {  
    Properties props = new Properties();  
    props.load(fs);  
    String url = props.getProperty
    
    ("db.url");  
    String 
    
    userName = props.getProperty("db.user");  
    String password = props.getProperty
    
    ("db.password");  
    Class.forName(driverClass);  
    
    con=DriverManager.getConnection(url, 
    
    userName, password);  
    }  
    
    public void fetch() throws SQLException, 
    
    IOException  
    {  
    PreparedStatement ps = 
    
    con.prepareStatement("select SYSDATE from dual");  
    ResultSet rs = ps.executeQuery
    
    ();  
    
    while 
    
    (rs.next())  
    {  
    // do the 
    
    thing you do  
    }
    
      
    rs.close();  
    ps.close();  
    }  
    
    public 
    
    static void main(String[] args)  
    {  
    OracleJdbcTest test = new 
    
    OracleJdbcTest();  
    test.init();  
    test.fetch
    
    ();  
    }  
    }  
    public class OracleJdbcTest
    {
          
    String driverClass = 
    
    "oracle.jdbc.driver.OracleDriver"; Connection con; public void init(FileInputStream fs) throws ClassNotFoundException, SQLException, FileNotFoundException, IOException
    {
          
    Properties props = new Properties();
    props.load
    
    (fs);
    String url = props.getProperty
    
    ("db.url");
    String userName = props.getProperty
    
    ("db.user");
    String password = props.getProperty
    
    ("db.password");
    Class.forName(driverClass); con=DriverManager.getConnection(url, userName, 
    
    password);
    } public void fetch() throws SQLException, IOException
    {
          
    PreparedStatement ps = con.prepareStatement("select SYSDATE from dual");
    ResultSet rs = ps.executeQuery(); while (rs.next())
    {
          
    // do the 
    
    thing you do
    }
    rs.close();
    ps.close
    
    ();
    } public static void main(String[] args)
    {
          
    OracleJdbcTest test = new OracleJdbcTest
    
    ();
    test.init();
    test.fetch();
    }
    }

6.将Java中的util.Date转换成**sql**.Date

这一片段显示如何将一个java util Date转换成sql Date用于**数据库**

<table style="width: 400px;"> 
 <tbody> 
  <tr> 
   <td> <pre>java.util.Date utilDate = new 
java.util.Date();&nbsp;&nbsp;<br>java.sql.Date sqlDate = new java.sql.Date
(utilDate.getTime());&nbsp;<p>&nbsp;</p><p>java.util.Date utilDate = new java.util.Date();<br>java.sql.Date sqlDate = 
new java.sql.Date(utilDate.getTime());</p></pre> </td> 
  </tr> 
 </tbody> 
</table>

7. 使用NIO快速复制Java文件

public static void fileCopy( File in, File out )
    
      
    throws IOException  
    {  
    FileChannel inChannel = new 
    
    FileInputStream( in ).getChannel();  
    FileChannel utChannel = new 
    
    FileOutputStream( out ).getChannel();  
    try 
    {  
    //          inChannel.transferTo
    
    (0, inChannel.size(), outChannel);      // original   -- apparently has trouble copying large files on Windows  
    
    // magic 
    
    number for Windows, 64Mb - 32Kb)  
    int maxCount 
    
    = (64 * 1024 * 1024) - (32 * 1024);  
    long size = 
    
    inChannel.size();  
    long 
    
    position = 0;  
    while ( 
    
    position < size )  
    {  
    &
    
    nbsp; position += inChannel.transferTo( position, maxCount, outChannel );  
    }
    
      
    }  
    finally 
    {  
    if ( 
    
    inChannel != null )  
    {  
    &
    
    nbsp; inChannel.close();  
    }
    
      
    if ( outChannel != null )  
    {  
    &
    
    nbsp;  outChannel.close();  
    }
    
      
    }  
    }  
    public static void fileCopy( File in, File out )
    throws 
    
    IOException
    {
          
    FileChannel inChannel = new FileInputStream( in ).getChannel
    
    ();
    FileChannel utChannel = new 
    
    FileOutputStream( out ).getChannel();
    try
    {
          
    //          inChannel.transferTo
    
    (0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows // magic 
    
    number for Windows, 64Mb - 32Kb)
    int maxCount 
    
    = (64 * 1024 * 1024) - (32 * 
    
    1024);
    long 
    
    size = inChannel.size
    
    ();
    long 
    
    position = 0;
    while ( position < size )
    {
          
      position += inChannel.transferTo( position, maxCount, outChannel 
    
    );
    }
    }
    finally
    {
          
    if ( 
    
    inChannel != null )
    {
          
      inChannel.close
    
    ();
    }
    if ( 
    
    outChannel != null )
    {
          
       outChannel.close
    
    ();
    }
    }
    }

8. 在Java中创建缩略图

private void createThumbnail(String filename, int thumbWidth, 
    
    int thumbHeight, int   quality, String outFilename)  
    throws InterruptedException, 
    
    FileNotFoundException, IOException  
    {  
    // load image from 
    
    filename  
    Image image = 
    
    Toolkit.getDefaultToolkit().getImage(filename);  
    MediaTracker mediaTracker = new 
    
    MediaTracker(new Container());  
    mediaTracker.addImage(image, 
    
    0);  
    mediaTracker.waitForID(0);  
    // use this to test for errors at 
    
    this point: System.out.println (mediaTracker.isErrorAny());  
    
    // determine thumbnail size from 
    
    WIDTH and HEIGHT  
    double 
    
    thumbRatio = (double)thumbWidth / (double)thumbHeight;  
    int imageWidth = image.getWidth
    
    (null);  
    int imageHeight 
    
    = image.getHeight(null);  
    double imageRatio = (double)imageWidth / (double)imageHeight;  
    if (thumbRatio < imageRatio) 
    
    {  
    thumbHeight 
    
    = (int)(thumbWidth / imageRatio);  
    } else {  
    thumbWidth = 
    
    (int)(thumbHeight * imageRatio);  
    }  
    
    // draw original image to thumbnail 
    
    image object and  
    // 
    
    scale it to the new size on-the-fly  
    BufferedImage thumbImage = new 
    
    BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);  
    Graphics2D graphics2D = 
    
    thumbImage.createGraphics();  
    graphics2D.setRenderingHint
    
    (RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);  
    graphics2D.drawImage(image, 0, 0, 
    
    thumbWidth, thumbHeight, null);  
    
    // save thumbnail image to 
    
    outFilename  
    BufferedOutputStream ut = new BufferedOutputStream(new FileOutputStream (outFilename));  
    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);  
    JPEGEncodeParam param = 
    
    encoder.getDefaultJPEGEncodeParam(thumbImage);  
    quality = Math.max(0, Math.min
    
    (quality, 100));  
    param.setQuality((float)quality / 100.0f, false);  
    encoder.setJPEGEncodeParam
    
    (param);  
    encoder.encode
    
    (thumbImage);  
    out.close
    
    ();  
    }  
    private void createThumbnail(String filename, int thumbWidth, int 
    
    thumbHeight, int quality, String outFilename)
    throws InterruptedException, 
    
    FileNotFoundException, IOException
    {
          
    // load image from 
    
    filename
    Image image = Toolkit.getDefaultToolkit().getImage
    
    (filename);
    MediaTracker mediaTracker = new MediaTracker(new 
    
    Container());
    mediaTracker.addImage(image, 
    
    0);
    mediaTracker.waitForID(0);
    // use this to test 
    
    for errors at this point: System.out.println (mediaTracker.isErrorAny()); // determine thumbnail size from WIDTH and 
    
    HEIGHT
    double thumbRatio = (double)thumbWidth / (double)
    
    thumbHeight;
    int imageWidth = image.getWidth
    
    (null);
    int imageHeight = image.getHeight
    
    (null);
    double imageRatio = (double)imageWidth / (double)
    
    imageHeight;
    if (thumbRatio < imageRatio) 
    
    {
          
    thumbHeight = (int)(thumbWidth / 
    
    imageRatio);
    } else {
          
    thumbWidth = (int)
    
    (thumbHeight * imageRatio);
    } // draw original image to thumbnail image object 
    
    and
    // scale it to the new size on-the-
    
    fly
    BufferedImage thumbImage = new BufferedImage(thumbWidth, thumbHeight, BufferedImage.TYPE_INT_RGB);
    Graphics2D graphics2D = 
    
    thumbImage.createGraphics();
    graphics2D.setRenderingHint
    
    (RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
    graphics2D.drawImag
    
    e(image, 0, 0, thumbWidth, thumbHeight, null); // save thumbnail image to 
    
    outFilename
    BufferedOutputStream ut = new BufferedOutputStream(new FileOutputStream(outFilename));
    JPEGImageEncoder encoder = 
    
    JPEGCodec.createJPEGEncoder(out);
    JPEGEncodeParam param = 
    
    encoder.getDefaultJPEGEncodeParam (thumbImage);
    quality = Math.max(0, Math.min(quality, 
    
    100));
    param.setQuality((float)quality / 100.0f, 
    
    false);
    encoder.setJPEGEncodeParam
    
    (param);
    encoder.encode(thumbImage);
    out.close
    
    ();
    }

9. 在Java中创建JSON数据

Read this article for more details.
    Download JAR file json
    
    -rpc-1.0.jar (75 kb)   
    
    import org.json.JSONObject;  
    ...  
    ...  
    JSONObject json = new JSONObject();  
    json.put("city", "Mumbai");  
    json.put("country", 
    
    "India");  
    ...  
    String utput = json.toString
    
    ();  
    ...  
    import org.json.JSONObject;
    ...
    ...
    JSONObject json = new 
    
    JSONObject();
    json.put("city", "Mumbai");
    json.put("country", 
    
    "India");
    ...
    String utput = json.toString();
    ...

10. 在Java中使用iText JAR打开PDF

Read this article for more details.   
    
    import java.io.File;  
    import 
    
    java.io.FileOutputStream;  
    import java.io.OutputStream;  
    import java.util.Date;  
    
    import 
    
    com.lowagie.text.Document;  
    import 
    
    com.lowagie.text.Paragraph;  
    import 
    
    com.lowagie.text.pdf.PdfWriter;  
    
    public class GeneratePDF 
    
    {  
    
    public static void main(String[] 
    
    args) {  
    try 
    
    {  
    OutputStream 
    
    file = new FileOutputStream(new File("C://Test.pdf"));  
    
    Document 
    
    document = new Document();  
    PdfWriter.getInstance(document, file);  
    document.open();  
    document.add(new Paragraph("Hello Kiran"));  
    document.add(new Paragraph(new Date().toString()));  
    
    document.close();  
    file.close
    
    ();  
    
    } catch 
    
    (Exception e) {  
    
    e.printStackTrace();  
    }
    
      
    }  
    }  
    import java.io.File;
    import java.io.FileOutputStream;
    import 
    
    java.io.OutputStream;
    import java.util.Date; import com.lowagie.text.Document;
    import 
    
    com.lowagie.text.Paragraph;
    import com.lowagie.text.pdf.PdfWriter; public class GeneratePDF {
          public static void main(String[] args) 
    
    {
          
    try 
    
    {
          
    OutputStream file = new FileOutputStream(new File("C://Test.pdf")); Document 
    
    document = new Document
    
    ();
    PdfWriter.getInstance(document, 
    
    file);
    document.open
    
    ();
    document.add(new Paragraph("Hello 
    
    Kiran"));
    document.add(new Paragraph(new Date().toString())); document.close
    
    ();
    file.close(); } catch (Exception e) {
          e.printStackTrace();
    }
    }
    }

11. 在Java上的HTTP代理设置

System.getProperties().put("http.proxyHost", 
    
    "someProxyURL");  
    System.getProperties().put("http.proxyPort", 
    
    "someProxyPort");  
    System.getProperties().put("http.proxyUser", 
    
    "someUserName");  
    System.getProperties().put("http.proxyPassword", 
    
    "somePassword");    
    System.getProperties().put("http.proxyHost", 
    
    "someProxyURL");
    System.getProperties().put("http.proxyPort", 
    
    "someProxyPort");
    System.getProperties().put("http.proxyUser", 
    
    "someUserName");
    System.getProperties().put("http.proxyPassword", 
    
    "somePassword");

12. Java Singleton 例子

Read this article for more 
    
    details.
    Update: Thanks Markus for the comment. I have updated the code and 
    
    changed it to   more robust implementation. 
    
    public class SimpleSingleton {  
    private static SimpleSingleton singleInstance =  new SimpleSingleton
    
    ();  
    
    //Marking default constructor 
    
    private  
    //to avoid direct 
    
    instantiation.  
    private SimpleSingleton() 
    
    {  
    }  
    
    //Get instance for class SimpleSingleton  
    public static SimpleSingleton getInstance() {  
    
    return 
    
    singleInstance;  
    }  
    }  
    public class SimpleSingleton {
           
    private static SimpleSingleton 
    
    singleInstance =  new SimpleSingleton(); //Marking default constructor private
    //to avoid direct 
    
    instantiation.
    private SimpleSingleton() {
           
    } //Get instance for class SimpleSingleton
    public static 
    
    SimpleSingleton getInstance() {
           return singleInstance;
    }
    }
    One more implementation of 
    
    Singleton class. Thanks to Ralph and Lukasz Zielinski for pointing this out. 
    
    public enum SimpleSingleton {  
    INSTANCE;  
    public void doSomething() 
    
    {  
    }  
    }  
    
    //Call the method from Singleton:  
    SimpleSingleton.INSTANCE.doSomething();  
    public enum SimpleSingleton {
           
    INSTANCE;
    public void 
    
    doSomething() {
           
    }
    } //Call the method from Singleton:
    SimpleSingleton.INSTANCE.doSomething();

13. 在Java上做屏幕截图

Read this article for more details.   
    import 
    
    java.awt.Dimension;  
    import java.awt.Rectangle;  
    import java.awt.Robot;  
    import java.awt.Toolkit;  
    import java.awt.image.BufferedImage;  
    import 
    
    javax.imageio.ImageIO;  
    import java.io.File;  
    
    ...  
    
    public void captureScreen(String fileName) 
    
    throws Exception {  
    
    Dimension screenSize = 
    
    Toolkit.getDefaultToolkit().getScreenSize();  
    Rectangle 
    
    screenRectangle = new Rectangle(screenSize);  
    Robot 
    
    robot = new Robot();  
    BufferedImage image = 
    
    robot.createScreenCapture(screenRectangle);  
    ImageIO.write(image, "png", new File(fileName));  
    
    }
    
      
    ...  
    import java.awt.Dimension;
    import java.awt.Rectangle;
    import 
    
    java.awt.Robot;
    import java.awt.Toolkit;
    import 
    
    java.awt.image.BufferedImage;
    import javax.imageio.ImageIO;
    import 
    
    java.io.File; ... public void captureScreen(String fileName) throws Exception {
           Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize
    
    ();
    Rectangle screenRectangle = new Rectangle
    
    (screenSize);
    Robot robot = new Robot();
    BufferedImage image = robot.createScreenCapture(screenRectangle);
    ImageIO.write(image, "png", new File(fileName)); }
    ...

14. 在Java中的文件，目录列表

>File dir = new File("directoryName");  
    String[] children = dir.list();  
    if (children == 
    
    null) {  
    // Either dir does not exist 
    
    or is not a directory  
    } else {  
    for (int i=0; i < children.length; i++) 
    
    {  
    // Get 
    
    filename of file or directory  
    String filename = 
    
    children[i];  
    }  
    }  
    
    // It is also possible to filter the 
    
    list of returned files.  
    // This example does not return any 
    
    files that start with `.'.  
    FilenameFilter filter = new 
    
    FilenameFilter() {  
    public boolean 
    
    accept(File dir, String name) {  
    return !name.startsWith
    
    (".");  
    }  
    };  
    children = dir.list(filter);  
    
    // The list of files can also be retrieved as File objects  
    File[] files = dir.listFiles();  
    
    // 
    
    This filter only returns directories  
    FileFilter fileFilter = 
    
    new FileFilter() {  
    public boolean 
    
    accept(File file) {  
    return file.isDirectory
    
    ();  
    }  
    };  
    files = dir.listFiles(fileFilter);    
    File dir = new File("directoryName");
    String[] 
    
    children = dir.list();
    if (children == null) 
    
    {
           
    // Either dir does not exist or is 
    
    not a directory
    } else 
    
    {
           
    for (int i=0; i < 
    
    children.length; i++) 
    
    {
           
    // Get 
    
    filename of file or 
    
    directory
    String filename = children[i];
    }
    } // It is also possible to filter the list of returned 
    
    files.
    // This example does not return any files that start 
    
    with `.'.
    FilenameFilter filter = new FilenameFilter() 
    
    {
           
    public boolean accept(File dir, 
    
    String name) 
    
    {
           
    return !
    
    name.startsWith(".");
    }
    };
    children = dir.list(filter); // The list of files can also be retrieved as File 
    
    objects
    File[] files = dir.listFiles(); // This filter only returns directories
    FileFilter fileFilter = new FileFilter() 
    
    {
           
    public boolean accept(File file) 
    
    {
           
    return 
    
    file.isDirectory();
    }
    };
    files = dir.listFiles
    
    (fileFilter);

15. 在Java中创建ZIP和JAR文件

import java.util.zip.*;  
    import 
    
    java.io.*;  
    
    public class ZipIt {  
    public static void main(String args[]) throws IOException 
    
    {  
    if (args.length < 
    
    2) {  
    System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");  
    System.exit
    
    (-1);  
    }  
    File zipFile = new File(args
    
    [0]);  
    if 
    
    (zipFile.exists()) {  
    System.err.println("Zip file already exists, please try another");  
    System.exit
    
    (-2);  
    }  
    FileOutputStream fos = new 
    
    FileOutputStream(zipFile);  
    ZipOutputStream zos = new 
    
    ZipOutputStream(fos);  
    int bytesRead;  
    byte[] 
    
    buffer = new byte[1024];  
    CRC32 crc = new CRC32();  
    for (int i=1, n=args.length; i < n; i++) {  
    String name 
    
    = args[i];  
    File file = 
    
    new File(name);  
    if (!
    
    file.exists()) {  
    &
    
    nbsp;  System.err.println("Skipping: " + name);  
    &
    
    nbsp;  continue;  
    }
    
      
    BufferedInputStream bis = new BufferedInputStream(  
    &
    
    nbsp;  new FileInputStream(file));  
    crc.reset
    
    ();  
    while 
    
    ((bytesRead = bis.read(buffer)) != -1) {  
    &
    
    nbsp;  crc.update(buffer, 0, bytesRead);  
    }
    
      
    bis.close();  
    // Reset to 
    
    beginning of input stream  
    bis = new 
    
    BufferedInputStream(  
    &
    
    nbsp;  new FileInputStream(file));  
    ZipEntry 
    
    entry = new ZipEntry(name);  
    entry.setMethod(ZipEntry.STORED);  
    entry.setCompressedSize(file.length());  
    entry.setSize(file.length());  
    entry.setCrc(crc.getValue());  
    zos.putNextEntry(entry);  
    while 
    
    ((bytesRead = bis.read(buffer)) != -1) {  
    &
    
    nbsp;  zos.write(buffer, 0, bytesRead);  
    }
    
      
    bis.close();  
    }
    
      
    zos.close
    
    ();  
    }  
    }    
    import java.util.zip.*;
    import java.io.*; public class ZipIt {
            
    public static void main(String args
    
    []) throws IOException {
            
    if 
    
    (args.length < 2) 
    
    {
            
    System.err.println("usage: java ZipIt Zip.zip file1 file2 
    
    file3");
    System.exit(-1);
    }
    File zipFile = new File(args
    
    [0]);
    if (zipFile.exists()) 
    
    {
            
    System.err.println("Zip file already exists, please try 
    
    another");
    System.exit(-2);
    }
    FileOutputStream fos = new 
    
    FileOutputStream(zipFile);
    ZipOutputStream zos = new ZipOutputStream
    
    (fos);
    int 
    
    bytesRead;
    byte[] buffer = new byte
    
    [1024];
    CRC32 crc = new CRC32
    
    ();
    for (int i=1, n=args.length; i 
    
    < n; i++) 
    
    {
            
    String name 
    
    = args[i];
    File file = new File
    
    (name);
    if 
    
    (!file.exists()) 
    
    {
            
       System.err.println("Skipping: " + 
    
    name);
    &
    
    nbsp;   
    
    continue;
    }
    BufferedInputStream bis = new BufferedInputStream
    
    (
       new FileInputStream
    
    (file));
    crc.reset();
    while ((bytesRead = bis.read(buffer)) != -1) 
    
    {
            
       crc.update(buffer, 0, 
    
    bytesRead);
    }
    bis.close
    
    ();
    // Reset 
    
    to beginning of input 
    
    stream
    bis = 
    
    new BufferedInputStream
    
    (
       new FileInputStream
    
    (file));
    ZipEntry entry = new ZipEntry
    
    (name);
    entry.setMethod
    
    (ZipEntry.STORED);
    &
    
    nbsp; entry.setCompressedSize(file.length
    
    ());
    entry.setSize(file.length
    
    ());
    entry.setCrc(crc.getValue
    
    ());
    zos.putNextEntry
    
    (entry);
    while ((bytesRead = bis.read(buffer)) != -1) 
    
    {
            
       zos.write(buffer, 0, 
    
    bytesRead);
    }
    bis.close
    
    ();
    }
    zos.close();
    }
    }
    16. Parsing / Reading XML file in Java
    Sample XML file. 
    
    
            
     
     
    John 
    B 
    12 
     
     
    Mary 
    A 
    11 
     
     
    Simon 
    A 
    18 
     
      
    
           
    
    
    John
    B
    12
    
    
    Mary
    A
    <
    
    AGE>11
    
    
    Simon
    A
    18
    
    
    Java code to parse above XML. 
    
    package net.viralpatel.java.xmlparser;  
    
    import java.io.File;  
    import 
    
    javax.xml.parsers.DocumentBuilder;  
    import 
    
    javax.xml.parsers.DocumentBuilderFactory;  
    
    import 
    
    org.w3c.dom.Document;  
    import org.w3c.dom.Element;  
    import org.w3c.dom.Node;  
    import 
    
    org.w3c.dom.NodeList;  
    
    public class XMLParser 
    
    {  
    
    public void getAllUserNames(String 
    
    fileName) {  
    try 
    
    {  
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
    DocumentBuilder db = dbf.newDocumentBuilder();  
    File file = 
    
    new File(fileName);  
    if 
    
    (file.exists()) {  
    &
    
    nbsp;  Document doc = db.parse(file);  
    &
    
    nbsp;  Element docEle = doc.getDocumentElement();  
    
    &
    
    nbsp;  // Print root element of the document  
    &
    
    nbsp;  System.out.println("Root element of the document: " 
    &
    
    nbsp;          + docEle.getNodeName
    
    ());  
    
    &
    
    nbsp;  NodeList studentList = docEle.getElementsByTagName
    
    ("student");  
    
    &
    
    nbsp;  // Print total student elements in document  
    &
    
    nbsp;  System.out  
    &
    
    nbsp;          .println("Total 
    
    students: " + studentList.getLength());  
    
    &
    
    nbsp;  if (studentList != null && studentList.getLength() > 0) 
    
    {  
    &
    
    nbsp;      for (int i = 0; i < studentList.getLength(); 
    
    i++) {  
    
    &
    
    nbsp;          Node node = 
    
    studentList.item(i);  
    
    &
    
    nbsp;          if (node.getNodeType() 
    
    == Node.ELEMENT_NODE) {  
    
    &
    
    nbsp;              
    
    System.out  
    &
    
    nbsp;             
    
             .println
    
    ("=====================");  
    
    &
    
    nbsp;              
    
    Element e = (Element) node;  
    &
    
    nbsp;              
    
    NodeList nodeList = e.getElementsByTagName("name");  
    &
    
    nbsp;              
    
    System.out.println("Name: " 
    &
    
    nbsp;             
    
             + nodeList.item(0).getChildNodes
    
    ().item(0)  
    &
    
    nbsp;             
    
                  
    
    ;   .getNodeValue());  
    
    &
    
    nbsp;              
    
    nodeList = e.getElementsByTagName("grade");  
    &
    
    nbsp;              
    
    System.out.println("Grade: " 
    &
    
    nbsp;             
    
             + nodeList.item(0).getChildNodes
    
    ().item(0)  
    &
    
    nbsp;             
    
                  
    
    ;   .getNodeValue());  
    
    &
    
    nbsp;              
    
    nodeList = e.getElementsByTagName("age");  
    &
    
    nbsp;              
    
    System.out.println("Age: " 
    &
    
    nbsp;             
    
             + nodeList.item(0).getChildNodes
    
    ().item(0)  
    &
    
    nbsp;             
    
                  
    
    ;   .getNodeValue());  
    &
    
    nbsp;          }  
    &
    
    nbsp;      }  
    &
    
    nbsp;  } else {  
    &
    
    nbsp;      System.exit(1);  
    &
    
    nbsp;  }  
    }
    
      
    } catch (Exception e) 
    
    {  
    System.out.println(e);  
    }  
    }  
    public 
    
    static void main(String[] args) {  
    
    XMLParser parser = new XMLParser
    
    ();  
    parser.getAllUserNames("c://test.xml");  
    }
    
      
    }  
    package net.viralpatel.java.xmlparser; import java.io.File;
    import javax.xml.parsers.DocumentBuilder;
    import 
    
    javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document;
    import org.w3c.dom.Element;
    import 
    
    org.w3c.dom.Node;
    import org.w3c.dom.NodeList; public class XMLParser {
            public void getAllUserNames(String fileName) {
            
    try 
    
    {
            
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = 
    
    dbf.newDocumentBuilder();
    File file = new File
    
    (fileName);
    if (file.exists()) 
    
    {
            
    Document doc = db.parse
    
    (file);
    Element docEle = doc.getDocumentElement(); // Print root element of the 
    
    document
    System.out.println("Root element of the 
    
    document: "
    + docEle.getNodeName()); NodeList studentList = docEle.getElementsByTagName ("student"); // Print total student elements in 
    
    document
    System.out
    &nb
    
    sp;.println("Total students: " + studentList.getLength()); if (studentList != null && 
    
    studentList.getLength() > 0) {
            
    for (int i = 0; i < 
    
    studentList.getLength (); i++) {
            Node node = studentList.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) {
            System.out
         .println ("====================="); Element e = (Element) 
    
    node;
    NodeList nodeList = e.getElementsByTagName
    
    ("name");
    System.out.println("Name: 
    
    "
    + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); nodeList = e.getElementsByTagName
    
    ("grade");
    System.out.println("Grade: "
    + nodeList.item(0).getChildNodes().item(0) .getNodeValue()); nodeList = e.getElementsByTagName
    
    ("age");
    System.out.println("Age: 
    
    "
    + nodeList.item(0).getChildNodes().item(0) .getNodeValue());
    }
    }
    } else 
    
    {
            
    System.exit(1);
    }
    }
    } catch (Exception e) 
    
    {
            
    System.out.println(e);
    }
    }
    public static void main(String[] args) {
            XMLParser parser = new XMLParser
    
    ();
    parser.getAllUserNames("c://test.xml");
    }
    }
    17. 
    
    Convert Array to Map in Java 
    import java.util.Map;  
    import 
    
    org.apache.commons.lang.ArrayUtils;  
    
    public class Main 
    
    {  
    
    public static void main(String[] args) 
    
    {  
    String[][] countries = { { "United States", 
    
    "New York" }, { "United Kingdom", "London" },  
    { 
    
    "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };  
    
    Map countryCapitals = 
    
    ArrayUtils.toMap(countries);  
    
    System.out.println("Capital of Japan is " + countryCapitals.get
    
    ("Japan"));  
    System.out.println("Capital of 
    
    France is " + countryCapitals.get("France"));  
    }  
    }  
    import java.util.Map;
    import org.apache.commons.lang.ArrayUtils; public class Main {
            public static void main(String[] args) {
            
    String[][] 
    
    countries = { { "United States", "New York" }, { "United Kingdom", "London" },
    { "Netherland", 
    
    "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } }; Map countryCapitals = ArrayUtils.toMap(countries); System.out.println("Capital of Japan is " + 
    
    countryCapitals.get("Japan"));
    System.out.println("Capital of 
    
    France is " + countryCapitals.get("France"));
    }
    }
    18. Send Email 
    
    using Java 
    import javax.mail.*;  
    import 
    
    javax.mail.internet.*;  
    import java.util.*;  
    
    public void postMail( String recipients[ ], String subject, String message , 
    
    String from) throws MessagingException  
    {  
    boolean debug = false;  
    
    //Set the host smtp address  
    Properties props = new Properties();  
    props.put("mail.smtp.host", 
    
    "smtp.example.com");  
    
    // create some 
    
    properties and get the default Session  
    Session 
    
    session = Session.getDefaultInstance(props, null);  
    session.setDebug(debug);  
    
    // create a message  
    Message msg = new MimeMessage(session);  
    
    // set the from and to address  
    InternetAddress addressFrom = new InternetAddress
    
    (from);  
    msg.setFrom(addressFrom);  
    
    InternetAddress[] addressTo = new 
    
    InternetAddress[recipients.length];  
    for (int i = 
    
    0; i < recipients.length; i++)  
    {  
    addressTo[i] = new InternetAddress
    
    (recipients[i]);  
    }  
    msg.setRecipients(Message.RecipientType.TO, 
    
    addressTo);  
    
    // Optional : You can 
    
    also set your custom headers in the Email if you Want  
    msg.addHeader("MyHeaderName", "myHeaderValue");  
    
    // Setting the Subject and Content 
    
    Type  
    msg.setSubject(subject);  
    msg.setContent(message, "text/plain");  
    Transport.send(msg);  
    }  
    import javax.mail.*;
    import javax.mail.internet.*;
    import 
    
    java.util.*; public void postMail( String recipients[ ], String subject, String message , 
    
    String from) throws MessagingException
    {
            
    boolean debug = 
    
    false; //Set the host smtp address
    Properties props = new Properties();
    props.put
    
    ("mail.smtp.host", "smtp.example.com"); // create some properties and get the default 
    
    Session
    Session session = Session.getDefaultInstance(props, 
    
    null);
    session.setDebug(debug); // create a message
    Message msg = new 
    
    MimeMessage(session); // set the from and to address
    InternetAddress addressFrom = new InternetAddress(from);
    msg.setFrom(addressFrom); InternetAddress[] addressTo = new InternetAddress
    
    [recipients.length];
    for (int i = 0; i < 
    
    recipients.length; i++)
    {
            
    addressTo[i] = new InternetAddress
    
    (recipients[i]);
    }
    msg.setRecipients
    
    (Message.RecipientType.TO, addressTo); // Optional : You can also set your custom headers in the 
    
    Email if you Want
    msg.addHeader("MyHeaderName", 
    
    "myHeaderValue"); // Setting the Subject and Content Type
    msg.setSubject(subject);
    msg.setContent(message, 
    
    "text/plain");
    Transport.send(msg);
    }
    19. Send HTTP 
    
    request & fetching data using Java 
    import java.io.BufferedReader;  
    import 
    
    java.io.InputStreamReader;  
    import java.net.URL;  
    
    public class Main {  
    public static 
    
    void main(String[] args)  {  
    try {  
    URL my_url = 
    
    new URL("http://www.viralpatel.net/blogs/");&nbs
    
    p; 
    BufferedReader br = new BufferedReader(new InputStreamReader (my_url.openStream()));  
    String 
    
    strTemp = "";  
    while(null 
    
    != (strTemp = br.readLine())){  
    System.out.println(strTemp);  
    }  
    } catch (Exception ex) {  
    ex.printStackTrace();  
    }
    
      
    }  
    }  
    import java.io.BufferedReader;
    import 
    
    java.io.InputStreamReader;
    import java.net.URL; public class Main {
            
    public static void main(String[] args)  
    
    {
            
    try {
            
    URL my_url = new URL("http://www.viralpatel.net/blogs/");
       BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
    String strTemp = 
    
    "";
    while(null != (strTemp = br.readLine()))
    
    {
            
    System.out.println(strTemp);
    }
    } catch (Exception ex) {
            
    ex.printStackTrace
    
    ();
    }
    }
    }
    20. Resize an Array in Java 
    /** 
    * Reallocates an array with a new size, and copies the 
    
    contents 
    * of the old array to the new array. 
    * @param 
    
    oldArray  the old array, to be reallocated. 
    * @param 
    
    newSize   the new array size. 
    * 
    
    @return          A new array with the 
    
    same contents. 
    */ 
    private static Object resizeArray (Object 
    
    oldArray, int newSize) {  
    int ldSize = 
    
    java.lang.reflect.Array.getLength(oldArray);  
    Class 
    
    elementType = oldArray.getClass().getComponentType();  
    Object newArray = java.lang.reflect.Array.newInstance(  
    elementType,newSize);  
    int preserveLength = Math.min
    
    (oldSize,newSize);  
    if (preserveLength > 0)
    
      
    System.arraycopy 
    
    (oldArray,0,newArray,0,preserveLength);  
    return 
    
    newArray;  
    }  
    
    // Test routine for 
    
    resizeArray().  
    public static void main (String[] args) 
    
    {  
    int[] a = {1,2,3};  
    a = 
    
    (int[])resizeArray(a,5);  
    a[3] = 4;  
    a[4] = 5;  
    for (int i=0; i      System.out.println (a[i]);  
    }

16. 在Java中解析/读取XML文件

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    <?xml version="1.0"?> 
    <students> 
    <student> 
    <name>John</name> 
    <grade>B</grade> 
    <age>12</age> 
    </student> 
    <student> 
    <name>Mary</name> 
    <grade>A</grade> 
    <age>11</age> 
    </student> 
    <student> 
    <name>Simon</name> 
    <grade>A</grade> 
    <age>18</age> 
    </student> 
    </students>    
    <?xml version="1.0"?>
    <students>
    <student>
    <name>John</name>
    <grade>B</grade>
    <age>12</age>
    </student>
    <student>
    <name>Mary</name>
    <grade>A</grade>
    <age>11</age>
    </student>
    <student>
    <name>Simon</name>
    <grade>A</grade>
    <age>18</age>
    </student>
    </students>
    Java code to parse above XML. view plaincopy to clipboardprint?
    
    package net.viralpatel.java.xmlparser;  
    
    import java.io.File;  
    import javax.xml.parsers.DocumentBuilder;  
    import javax.xml.parsers.DocumentBuilderFactory;  
    
    import org.w3c.dom.Document;  
    import org.w3c.dom.Element;  
    import org.w3c.dom.Node;  
    import org.w3c.dom.NodeList;  
    
    public class XMLParser {  
    
    public void getAllUserNames(String fileName) {  
    try {  
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
    DocumentBuilder db = dbf.newDocumentBuilder();  
    File file = new File(fileName);  
    if (file.exists()) {  
    Document doc = db.parse(file);  
    Element docEle = doc.getDocumentElement();  
    
    // Print root element of the document  
    System.out.println("Root element of the document: " 
    + docEle.getNodeName());  
    
    NodeList studentList = docEle.getElementsByTagName("student");  
    
    // Print total student elements in document  
    System.out  
    .println("Total students: " + studentList.getLength());  
    
    if (studentList != null && studentList.getLength() > 0) {  
    for (int i = 0; i < studentList.getLength(); i++) {  
    
    Node node = studentList.item(i);  
    
    if (node.getNodeType() == Node.ELEMENT_NODE) {  
    
    System.out  
    .println("=====================");  
    
    Element e = (Element) node;  
    NodeList nodeList = e.getElementsByTagName("name");  
    System.out.println("Name: " 
    + nodeList.item(0).getChildNodes().item(0)  
    .getNodeValue());  
    
    nodeList = e.getElementsByTagName("grade");  
    System.out.println("Grade: " 
    + nodeList.item(0).getChildNodes().item(0)  
    .getNodeValue());  
    
    nodeList = e.getElementsByTagName("age");  
    System.out.println("Age: " 
    + nodeList.item(0).getChildNodes().item(0)  
    .getNodeValue());  
    }  
    }  
    } else {  
    System.exit(1);  
    }  
    }  
    } catch (Exception e) {  
    System.out.println(e);  
    }  
    }  
    public static void main(String[] args) {  
    
    XMLParser parser = new XMLParser();  
    parser.getAllUserNames("c://test.xml");  
    }  
    }  
    package net.viralpatel.java.xmlparser; import java.io.File;
    import javax.xml.parsers.DocumentBuilder;
    import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document;
    import org.w3c.dom.Element;
    import org.w3c.dom.Node;
    import org.w3c.dom.NodeList; public class XMLParser {
           public void getAllUserNames(String fileName) {
           
    try {
           
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    File file = new File(fileName);
    if (file.exists()) {
           
    Document doc = db.parse(file);
    Element docEle = doc.getDocumentElement(); // Print root element of the document
    System.out.println("Root element of the document: "
    + docEle.getNodeName()); NodeList studentList = docEle.getElementsByTagName("student"); // Print total student elements in document
    System.out
    .println("Total students: " + studentList.getLength()); if (studentList != null && studentList.getLength() > 0) {
           
    for (int i = 0; i < studentList.getLength(); i++) {
           Node node = studentList.item(i); if (node.getNodeType() == Node.ELEMENT_NODE) {
           System.out
    .println("====================="); Element e = (Element) node;
    NodeList nodeList = e.getElementsByTagName("name");
    System.out.println("Name: "
    + nodeList.item(0).getChildNodes().item(0)
    .getNodeValue()); nodeList = e.getElementsByTagName("grade");
    System.out.println("Grade: "
    + nodeList.item(0).getChildNodes().item(0)
    .getNodeValue()); nodeList = e.getElementsByTagName("age");
    System.out.println("Age: "
    + nodeList.item(0).getChildNodes().item(0)
    .getNodeValue());
    }
    }
    } else {
           
    System.exit(1);
    }
    }
    } catch (Exception e) {
           
    System.out.println(e);
    }
    }
    public static void main(String[] args) {
           XMLParser parser = new XMLParser();
    parser.getAllUserNames("c://test.xml");
    }
    }

17. 在Java中将Array转换成Map

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    import java.util.Map;  
    import org.apache.commons.lang.ArrayUtils;  
    
    public class Main {  
    
    public static void main(String[] args) {  
    String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },  
    { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } };  
    
    Map countryCapitals = ArrayUtils.toMap(countries);  
    
    System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));  
    System.out.println("Capital of France is " + countryCapitals.get("France"));  
    }  
    }    
    import java.util.Map;
    import org.apache.commons.lang.ArrayUtils; public class Main {
           public static void main(String[] args) {
           
    String[][] countries = { { "United States", "New York" }, { "United Kingdom", "London" },
    { "Netherland", "Amsterdam" }, { "Japan", "Tokyo" }, { "France", "Paris" } }; Map countryCapitals = ArrayUtils.toMap(countries); System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));
    System.out.println("Capital of France is " + countryCapitals.get("France"));
    }
    }

18. 在Java中发送电子邮件

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    import javax.mail.*;  
    import javax.mail.internet.*;  
    import java.util.*;  
    
    public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException  
    {  
    boolean debug = false;  
    
    //Set the host smtp address  
    Properties props = new Properties();  
    props.put("mail.smtp.host", "smtp.example.com");  
    
    // create some properties and get the default Session  
    Session session = Session.getDefaultInstance(props, null);  
    session.setDebug(debug);  
    
    // create a message  
    Message msg = new MimeMessage(session);  
    
    // set the from and to address  
    InternetAddress addressFrom = new InternetAddress(from);  
    msg.setFrom(addressFrom);  
    
    InternetAddress[] addressTo = new InternetAddress[recipients.length];  
    for (int i = 0; i < recipients.length; i++)  
    {  
    addressTo[i] = new InternetAddress(recipients[i]);  
    }  
    msg.setRecipients(Message.RecipientType.TO, addressTo);  
    
    // Optional : You can also set your custom headers in the Email if you Want  
    msg.addHeader("MyHeaderName", "myHeaderValue");  
    
    // Setting the Subject and Content Type  
    msg.setSubject(subject);  
    msg.setContent(message, "text/plain");  
    Transport.send(msg);  
    }    
    import javax.mail.*;
    import javax.mail.internet.*;
    import java.util.*; public void postMail( String recipients[ ], String subject, String message , String from) throws MessagingException
    {
           
    boolean debug = false; //Set the host smtp address
    Properties props = new Properties();
    props.put("mail.smtp.host", "smtp.example.com"); // create some properties and get the default Session
    Session session = Session.getDefaultInstance(props, null);
    session.setDebug(debug); // create a message
    Message msg = new MimeMessage(session); // set the from and to address
    InternetAddress addressFrom = new InternetAddress(from);
    msg.setFrom(addressFrom); InternetAddress[] addressTo = new InternetAddress[recipients.length];
    for (int i = 0; i < recipients.length; i++)
    {
           
    addressTo[i] = new InternetAddress(recipients[i]);
    }
    msg.setRecipients(Message.RecipientType.TO, addressTo); // Optional : You can also set your custom headers in the Email if you Want
    msg.addHeader("MyHeaderName", "myHeaderValue"); // Setting the Subject and Content Type
    msg.setSubject(subject);
    msg.setContent(message, "text/plain");
    Transport.send(msg);
    }

19. 使用Java发送HTTP请求和提取数据

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    import java.io.BufferedReader;  
    import java.io.InputStreamReader;  
    import java.net.URL;  
    
    public class Main {  
    public static void main(String[] args)  {  
    try {  
    URL my_url = new URL("http://www.viralpatel.net/blogs/");  
    BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));  
    String strTemp = "";  
    while(null != (strTemp = br.readLine())){  
    System.out.println(strTemp);  
    }  
    } catch (Exception ex) {  
    ex.printStackTrace();  
    }  
    }  
    }    
    import java.io.BufferedReader;
    import java.io.InputStreamReader;
    import java.net.URL; public class Main {
           
    public static void main(String[] args)  {
           
    try {
           
    URL my_url = new URL("http://www.viralpatel.net/blogs/");
    BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream()));
    String strTemp = "";
    while(null != (strTemp = br.readLine())){
           
    System.out.println(strTemp);
    }
    } catch (Exception ex) {
           
    ex.printStackTrace();
    }
    }
    }

20. 在Java中调整数组

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    /** 
    * Reallocates an array with a new size, and copies the contents 
    * of the old array to the new array. 
    * @param oldArray  the old array, to be reallocated. 
    * @param newSize   the new array size. 
    * @return          A new array with the same contents. 
    */ 
    private static Object resizeArray (Object oldArray, int newSize) {  
    int ldSize = java.lang.reflect.Array.getLength(oldArray);  
    Class elementType = oldArray.getClass().getComponentType();