java前端重点_后端&前端零碎知识点

比眉伴天荒 2022-11-07 14:54 125阅读 0赞

后端

1. Spring自带的MD5加密工具类

importorg.springframework.util.DigestUtils;

String md5Password= DigestUtils.md5DigestAsHex(password.getBytes());

2. 数据库的字段名不要含有 is

比如数据库有个字段为is\_valid，那么到代码里这个变量为isValid。如果恰好这个变量是Boolean类型的，那么如果返回数据到前端，那么json串为\{"valid":true\}，可以看见is被无形去掉了。

![98fa8d273903ea692e26881544487a5f.png][]

看自动生成的get方法，没有get前缀，都是因为Boolean类型的get方法都是以is开头的，而这样会覆盖掉你名字里的is前缀，所以如果你的变量为Boolean类型命名要避免以is开头。

3. invalid comparison: org.springframework.web.bind.annotation.RequestMethod and java.lang.String

别人留下的坑：

mybatis里面的sql语句，org.springframework.web.bind.annotation.RequestMethod是个枚举类

REQUEST\_METHOD=\#\{requestMethod , jdbcType=VARCHAR, typeHandler=org.apache.ibatis.type.EnumTypeHandler\},

这里的判断：requestMethod != ''　导致报错，因为你一个枚举类怎么能跟字符串作比较呢？

4. 修改html页面，IDEA不自动部署的问题

首先禁用掉当前模板引擎的缓存，比如：spring.thymeleaf.cache=false，页面修改之后按Ctrl+F9重新Build Project

5. org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter 已废弃

自5.0版本开始，MVC相关配置可直接实现 org.springframework.web.servlet.config.annotation.WebMvcConfigurer

importcom.example.demo.interceptor.CommonInterceptor;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.context.annotation.Configuration;importorg.springframework.web.servlet.config.annotation.InterceptorRegistry;importorg.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configurationpublic class MyWebConfig implementsWebMvcConfigurer \{

@AutowiredprivateCommonInterceptor commonInterceptor;/\*\*\* 配置拦截器

\*@paramregistry\*/@Overridepublic voidaddInterceptors(InterceptorRegistry registry) \{

registry.addInterceptor(commonInterceptor).addPathPatterns("/\*\*").excludePathPatterns("/login");

6. 查看SpringBoot默认的配置类

在application.properties里面配置debug=true，在启动的时候就会打印开启的默认配置类。

![6f39855420e209e5da157d698c67e045.png][]

7. maven打包SpringBoot项目后，java -jar命令报错，找不到主清单属性

org.springframework.boot

spring-boot-maven-plugin

$\{spring.boot.version\}

package

repackage

8. Java解析HTML/XML字符串

dom4j

1.6.1

代码

importorg.dom4j.Document;importorg.dom4j.DocumentException;importorg.dom4j.DocumentHelper;importorg.dom4j.Element;importjava.util.HashMap;importjava.util.Map;public classTest \{public static void main(String\[\] args) throwsDocumentException \{

parse(create());

\}private staticString create()\{

Document document=DocumentHelper.createDocument();

Element rootElement= document.addElement("response");

Map postMap = new HashMap<>();

postMap.put("code", "200");

postMap.put("msg", "操作成功！");for(String key : postMap.keySet()) \{

Element element=rootElement.addElement(key);

element.setText(postMap.get(key));

String xml=document.getRootElement().asXML();

System.out.println("Create Result：" +xml);returnxml;

\}private static void parse(String data) throwsDocumentException \{

Document document=DocumentHelper.parseText(data);

Element rootElement=document.getRootElement();

System.out.println("==============Parse Result ==============");

System.out.println(rootElement.element("code").getText());

System.out.println(rootElement.element("msg").getText());

输出

![16650032cbd4aac2c66c98c82253fef6.png][]

9. 后端传递Long，前端精度丢失解决

importcom.fasterxml.jackson.annotation.JsonFormat;importcom.fasterxml.jackson.databind.annotation.JsonSerialize;importcom.fasterxml.jackson.databind.ser.std.ToStringSerializer;public classUser \{/\*\*\* 方法一\*/@JsonFormat(shape=JsonFormat.Shape.STRING)privateLong userId;/\*\*\* 方法二\*/@JsonSerialize(using= ToStringSerializer.class)privateLong orderId;

10. Integer对象转Comparable对象(来自JDK源码)

Integer x = 10;

Comparable key = (Comparable) x;

System.out.println(x.compareTo(1));

11. Optional的使用

List list = null;//无论list是否为空，都会执行orElse

List strings = Optional.ofNullable(list).orElse(new ArrayList<>());//只有list为空，才会执行orElseGet

List strings2 = Optional.ofNullable(list).orElseGet(ArrayList::new);

12. 解析Excel

引入依赖

org.apache.poi

poi

4.1.2

org.apache.poi

poi-ooxml

4.1.2

代码

importorg.apache.poi.hssf.usermodel.HSSFWorkbook;importorg.apache.poi.ss.usermodel.Cell;importorg.apache.poi.ss.usermodel.Row;importorg.apache.poi.ss.usermodel.Sheet;importorg.apache.poi.ss.usermodel.Workbook;importorg.apache.poi.xssf.usermodel.XSSFWorkbook;importjava.io.File;importjava.io.FileInputStream;importjava.io.IOException;importjava.util.ArrayList;importjava.util.List;public classMain \{public static void main(String\[\] args) throwsException \{

File file= new File("excel.xlsx");

readExcel(file);

\}private static void readExcel(File file) throwsIOException \{

FileInputStream in= newFileInputStream(file);

List codes = new ArrayList<>();

Workbook wb= null;//解析后缀

String prefix = file.getName().substring(file.getName().lastIndexOf(".") + 1);//根据后缀判断文件类型

if ("xls".equals(prefix))\{

wb= newHSSFWorkbook(in);

\}else if ("xlsx".equals(prefix))\{

wb= newXSSFWorkbook(in);

\}if (wb != null)\{//sheet数量

int numberOfSheets =wb.getNumberOfSheets();//遍历sheet

for (int i = 0; i < numberOfSheets; i++)\{

Sheet sheet=wb.getSheetAt(i);//遍历标题行(第0行)

Row title = sheet.getRow(0);

System.out.println("===============");for (int c = 0; c < title.getLastCellNum(); c++)\{

Cell cell=title.getCell(c);

System.out.print(selectCellType(cell)+ "\\t");

System.out.println("\\n===============");//遍历数据行(第1行开始)

for (int j = 1; j <= sheet.getLastRowNum(); j++)\{

Row row=sheet.getRow(j);for (int c = 0; c < row.getLastCellNum(); c++)\{

Cell cell=row.getCell(c);

System.out.print(selectCellType(cell)+ "\\t");

System.out.println();

\}private staticObject selectCellType(Cell cell)\{switch(cell.getCellType())\{caseBLANK:return "";caseSTRING:returncell.getStringCellValue();caseBOOLEAN:returncell.getBooleanCellValue();caseNUMERIC:returncell.getNumericCellValue();caseFORMULA:returncell.getCellFormula();default:return "";

测试：

![0e67a873d37560cb62ce8d718f8c676c.png][]

13. 按照逗号分隔的 String与List 互转

依赖

org.apache.commons

commons-lang3

3.10

代码

import org.apache.commons.lang3.StringUtils;

String text = "A,B,C,D,E";//--------------String转List

List stringList = Arrays.asList(text.split(","));//--------------List转String

String join = StringUtils.join(stringList, ",");

System.out.println(stringList+ "\\t\\t" + join);

测试：

![89417fb331b8d8f0c68c15a60f6f326e.png][]

14. 读取文件指定编码(再也不用写字符串"UTF-8"了)

//java.nio.charset.StandardCharsets

BufferedReader input= new BufferedReader(new InputStreamReader(new FileInputStream(""), StandardCharsets.UTF\_8));

15. Java8提供的String.join方法

List arr = new ArrayList<>();

String.join(",", arr);

前端

1. string转number

$('div').text(p+1);

\});

[98fa8d273903ea692e26881544487a5f.png]: /images/20221023/6ef751576952469b8703f820164d6007.png
[6f39855420e209e5da157d698c67e045.png]: /images/20221023/d47d543846234912929f1b0b6fe3ac97.png
[16650032cbd4aac2c66c98c82253fef6.png]: /images/20221023/e2af8c220f1f4a4e92f8fe2960c1321b.png
[0e67a873d37560cb62ce8d718f8c676c.png]: /images/20221023/031b5524b8b6474c81c57b67d5507e63.png
[89417fb331b8d8f0c68c15a60f6f326e.png]: /images/20221023/db46b431381e4eec9a971ed08876ea8e.png