【Java.Web】Servlet —— 实例 之 上传文件
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 files
try{
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 disk
File 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