Java中文件上传

怼烎@ 2022-08-23 03:48 112阅读 0赞

Java中文件上传一般通过借助第三方组件，听说Servlet3.0出来之后也可以用Servlet直接写文件上传，但是我这次还是通过借助Apache的common fileupload组件实现上传功能。

其中要想完成文件上传，必须有几个注意事项:

一：把form表单的enctype属性值设置为multipart/form-data

二：最好以post方式提交

三：表单中提供<input type="file"类型的上传输入域

其中form表单的enctype属性

该属性的作用是用来告知服务器，请求正文内容的MIME类型的。相当于请求消息头Content-Type。

在第一个上传页面中代码如下:

<%@ page language="java" contentType="text/html; charset=UTF-8"
        pageEncoding="UTF-8"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>文件上传demo</title>
    </head>
    <body>
    <form action="FileUploadServlet" enctype="multipart/form-data" method="post">
    姓名:<input type="text" name="name" /><br/>
    文件一:<input type="file" name="file1"/><br/>
    文件二:<input type="file" name="file2"/><br/>
    <input type="submit" value="上传"/>
    </form>
    </body>
    </html>

在文件处理servlet中代码如下:

package com.levi.fileUpload;
    
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    import java.io.UnsupportedEncodingException;
    import java.net.URL;
    import java.util.ArrayList;
    import java.util.List;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import org.apache.commons.fileupload.FileItem;
    import org.apache.commons.fileupload.FileUploadException;
    import org.apache.commons.fileupload.disk.DiskFileItemFactory;
    import org.apache.commons.fileupload.servlet.ServletFileUpload;
    import org.apache.commons.io.FileUtils;
    import org.apache.commons.io.FilenameUtils;
    
    public class FileUploadServlet extends HttpServlet {
    
    	public void doGet(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    		request.setCharacterEncoding("utf-8");
    		response.setCharacterEncoding("utf-8");
    		//检测form是否是multipart/form-data类型的
    		boolean isMultipart = ServletFileUpload.isMultipartContent(request);
    		if(!isMultipart){
    			throw new RuntimeException("form表单的enctype类型必须为 multipart/form-data");
    		}
    		//解析请求内容
    		DiskFileItemFactory factory = new DiskFileItemFactory();//产生FileItem的工厂
    		ServletFileUpload sfu = new ServletFileUpload(factory);
    		List<FileItem> items = new ArrayList<FileItem>();
    		try {
    			items = sfu.parseRequest(request);
    		} catch (FileUploadException e) {
    			throw new RuntimeException("解析请求失败");
    		}
    		//遍历：
    		for(FileItem item:items){
    			//处理普通字段
    			if(item.isFormField()){
    				processFormField(item);
    			}else{
    			//处理上传字段
    				processUploadField(item);
    			}
    		}
    	}
    
    	protected void processUploadField(FileItem item) {
    		try {
    //			InputStream in = item.getInputStream();
    			//找一个存放文件的位置；存放的文件名
    			String fileName = item.getName();//上传的文件的文件名 
    			if(fileName!=null){
    				fileName = FilenameUtils.getName(fileName);
    			}
    			//存放路径
    			//String realPath = getServletContext().getRealPath("/files");
    			String realPath=new String("d:\\UploadFile");//把上传的文件放到d盘下的这个文件夹
    		
    			File storeDirectory = new File(realPath);
    			if(!storeDirectory.exists()){
    				storeDirectory.mkdirs();
    			}
    			OutputStream out = new FileOutputStream(new File(storeDirectory, fileName));
    			InputStream in=item.getInputStream();
    			int len = -1;
    			byte b[] = new byte[1024];
    			while((len=in.read(b))!=-1){
    				out.write(b, 0, len);
    		}
    			in.close();
    			out.close();
    			//这个是借助提供插件的写文件。和前面几行手动写的代码是一样的
    			//item.write(new File(storeDirectory, fileName));
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	protected void processFormField(FileItem item) {
    		//打印到控制台
    		String fieldName = item.getFieldName();
    		String fieldValue = null;
    		
    			try
    			{
    				fieldValue = new String(item.getString("utf-8"));
    			} catch (UnsupportedEncodingException e)
    			{
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		
    			System.out.println(fieldName+"="+fieldValue);
    		
    	}
    
    	public void doPost(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

既然写了servlet，那就必须要配置servlet啦。相信你们肯定都会做。不过俺还是附web.xml中的配置

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
      <display-name>FileUpload</display-name>
      <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
      </welcome-file-list>
      <servlet>
        <description></description>
        <display-name>FileUploadServlet</display-name>
        <servlet-name>FileUploadServlet</servlet-name>
        <servlet-class>com.levi.fileUpload.FileUploadServlet</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>FileUploadServlet</servlet-name>
        <url-pattern>/FileUploadServlet</url-pattern>
      </servlet-mapping>
    </web-app>

结果:最后成功获取到了我上传时的姓名，并打印到控制台了

![Image 1][]

并且在D:\\UploadFile文件夹下也成功的出现了我们上传的文件。

![Image 1][]

包含的jar包为:

![Image 1][]

相关的jar包可以在Apache上下到，需要的朋友自己去百度然后下载。

[Image 1]: