【Java.Web】Servlet —— 实例之上传文件

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上传文件

上传文件是指把客户端的文件发送到服务器端。当客户端向服务器上传文件时，客户端发送的http请求正文采用multipart/form-data数据类型。

不管http请求正文为何种设局类型，Servlet容器都会把http请求包装成一个HttpServletRequest对象。

为了简化“multipart/form-data”数据类型的处理，可以利用apache commons fileupload工具包来处理，具体参见：Java.ThirdParty.Apache Commons File Upload。

创建一个名为：uploadfile.html的文件，定义一个用于上传文件的复合表单，表单的action为对应servlet的url-pattern

<!DOCTYPE html><html><head><meta charset="utf-8"><title>Upload Files</title></head><body>    <form method="post" enctype="multipart/form-data" action="uploadfile">    File Upload Testing:<br/>    Upload File 1: <input type="file" name="file1" size="30"/><br/>    Upload File 2: <input type="file" name="file2" size="30"/><br/>    <input type="submit" name="submit" value="Upload"/>    <input type="reset" name="reset" value="Reset"/>    </form></body></html>

在浏览器中访问：

http://localhost:8080/base-webapp/uploadfile.html

页面如下：

浏览器生成的http request如下：

创建一个Servlet用于处理提交的表单：

package com.gof.test.servlet;import java.util.List;import java.util.Iterator;import java.io.IOException;import java.io.PrintWriter;import java.io.File;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.FileCleanerCleanup;import org.apache.commons.fileupload.servlet.ServletFileUpload;import org.apache.commons.fileupload.FileItem;import org.apache.commons.io.FileCleaningTracker;public class UploadFileServlet extends HttpServlet {/** *  */private static final long serialVersionUID = 3396770132755929933L;private String filePath = null;private String tempFilePath = null;    public void init(ServletConfig config) throws ServletException {        super.init(config);                // get the property in servlet configuration in web.xml         filePath = getInitParameter("filePath");        tempFilePath = getInitParameter("tempFilePath");        // get the real path is disk        filePath = getServletContext().getRealPath(filePath);        tempFilePath = getServletContext().getRealPath(tempFilePath);    }protected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException{    PrintWriter out = resp.getWriter();    // For Chinese File Name    req.setCharacterEncoding("utf-8");    // Begin to parse the uploaded filestry{    DiskFileItemFactory factory = new DiskFileItemFactory();    // Set the factory constraints    // Set the buffer size for file upload when write to disk    factory.setSizeThreshold(4 * 1024);    // Set the temporary path    factory.setRepository(new File(tempFilePath));            // Create a new file upload handler    ServletFileUpload upload = new ServletFileUpload(factory);    // Set overall request size constraint    upload.setFileSizeMax(4 * 1024 * 1024);    // Parse the request    List<FileItem> items = upload.parseRequest(req);    // Process the uploaded items    Iterator<FileItem> iter = items.iterator();    while (iter.hasNext()){    FileItem item = iter.next();        if (item.isFormField()){    processFormFields(item, out);    }else{    processUploadFiles(item, out);    }    }        out.close();}catch (Exception e){e.printStackTrace();}    }private void processFormFields(FileItem item, PrintWriter out){String name = item.getFieldName();String value = item.getString();out.println("The file name is " + name + "; The value is " + value);}private void processUploadFiles(FileItem item, PrintWriter out) throws Exception{String fieldName = item.getFieldName();String fileName = item.getName();String contentType = item.getContentType();long sizeInBytes = item.getSize();if ((fileName == null) || (sizeInBytes == 0)){return;}// write the file to diskFile uploadedFile = new File(filePath + "/" + fileName);item.write(uploadedFile);out.println("The file " + fileName + " is saved; The size of the file is " + sizeInBytes + " bytes");}}

在web.xml中注册上面的servlet，并配置保存文件的参数和临时目录：/upload, /tempupload：

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  <display-name>Base Java Webapp</display-name>  <description>A Basic Maven Java Webapp Application</description>    <welcome-file-list>      <welcome-file>index.jsp</welcome-file>  </welcome-file-list>      <!-- test url: http://localhost:8080/base-webapp/download?filename=testreport.txt -->  <servlet>  <servlet-name>downloadtest</servlet-name>  <servlet-class>com.gof.test.servlet.DownloadServlet</servlet-class>  </servlet>  <servlet-mapping>      <servlet-name>downloadtest</servlet-name>      <url-pattern>/download</url-pattern>  </servlet-mapping>    <!-- test upload file: http://localhost:8080/base-webapp/uploadfile.html -->  <servlet>  <servlet-name>uploadfiletest</servlet-name>  <servlet-class>com.gof.test.servlet.UploadFileServlet</servlet-class>  <init-param>      <param-name>filePath</param-name>      <param-value>/upload</param-value>  </init-param>  <init-param>      <param-name>tempFilePath</param-name>      <param-value>/tempupload</param-value>  </init-param>  </servlet>  <servlet-mapping>      <servlet-name>uploadfiletest</servlet-name>      <url-pattern>/uploadfile</url-pattern>  </servlet-mapping>  </web-app>

在webapp的根目录（base-webapp）下，创建上面的两个目录：

在页面中选择文件并点击upload，浏览器将请求名为uploadfile的Servlet，在webapp的目录upload下，可以找到上传的文件：

该Servlet同时向客户端返回如下的页面：

http://localhost:8080/base-webapp/uploadfile

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【Java.Web】Servlet —— 实例 之 上传文件

上传文件

【Java.Web】Servlet —— 实例之上传文件