文件上传的方法主要目前有两个常用的，一个是SmartUpload，一个是Apache的Commons fileupload.
我们这里主要介绍下第二个的用法，首先要上传文件，注意几个问题：
1 form表单内，要添加空间<input type="file" name="myfile">
2 form表单的内容格式要定义成multipart/form-data格式
3 需要类库：1 commons-io.jar 2commons-fileupload-1.3.1.jar
接下来我们看下用法。
首先阅读Apache commons fileupload的官方文档可以发现下面几个常用的函数：
1 创建文件解析对象
复制代码代码如下:DiskFileUpload diskFileUpload = new DiskFileUpload();
2 进行文件解析后放在List中，因为这个类库支持多个文件上传，因此把结果会存在List中。
复制代码代码如下:List<FileItem> list = diskFileUpload.parseRequest(request);
3 获取上传文件，进行分析（不是必须）
复制代码代码如下:File remoteFile = new File(new String(fileItem.getName().getBytes(),"UTF-8"));
4 创建新对象，进行流拷贝
file1 = new File(this.getServletContext().getRealPath("attachment"),remoteFile.getName()); file1.getParentFile().mkdirs(); file1.createNewFile(); InputStream ins = fileItem.getInputStream(); OutputStream ous = new FileOutputStream(file1); try{ byte[] buffer = new byte[1024]; int len = 0; while((len = ins.read(buffer)) > -1) ous.write(buffer,0,len); out.println("以保存文件"+file1.getAbsolutePath()+"<br/>"); }finally{ ous.close(); ins.close(); }这样我们就完成了文件的上传。
fileUpload.html
<form action="servlet/UploadServlet" method="post" enctype="multipart/form-data"> <div align="center"> <fieldset> <legend>上传文件</legend><br/> <div align="left">上传文件1</div> <div align="left"> <input type="file" name="file1"/> </div> <div align="left">上传文件2</div> <div align="left"> <input type="file" name="file2"/> </div> <div> <div align='left'>上传文件说明1</div> <div align='left'><input type="text" name="description1"/></div> </div> <div> <div align='left'>上传文件说明2</div> <div align='left'><input type="text" name="description2"/></div> </div> <div> <div align='left'> <input type='submit' value="上传文件"/> </div> </div> </fieldset> </div> </form>
web.xml
<servlet> <servlet-name>UploadServlet</servlet-name> <servlet-class>com.test.hello.UploadServlet</servlet-class> </servlet><servlet-mapping> <servlet-name>UploadServlet</servlet-name> <url-pattern>/servlet/UploadServlet</url-pattern> </servlet-mapping>
UploadServlet.java
package com.test.hello;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.io.PrintWriter;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.DiskFileUpload;import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.FileUploadException;public class UploadServlet extends HttpServlet { /** * Constructor of the object. */ public UploadServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setCharacterEncoding("UTF-8"); response.getWriter().println("请以POST方式上传文件"); } /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ @SuppressWarnings({ "unchecked", "deprecation" }) public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { File file1 = null,file2=null; String description1 = null,description2 = null; response.setCharacterEncoding("UTF-8"); request.setCharacterEncoding("UTF-8"); response.setContentType("text/html"); PrintWriter out = response.getWriter(); DiskFileUpload diskFileUpload = new DiskFileUpload(); try{ List<FileItem> list = diskFileUpload.parseRequest(request); out.println("遍历所有的FileItem...<br/>"); for(FileItem fileItem : list){ if(fileItem.isFormField()){ if("description1".equals(fileItem.getFieldName())){ out.println("遍历到description1 ... <br/>"); description1 = new String(fileItem.getString().getBytes(),"UTF-8"); } if("description2".equals(fileItem.getFieldName())){ out.println("遍历到description2 ... <br/>"); description2 = new String(fileItem.getString().getBytes(),"UTF-8"); } }else{ if("file1".equals(fileItem.getFieldName())){ File remoteFile = new File(new String(fileItem.getName().getBytes(),"UTF-8")); out.println("遍历到file1...<br/>"); out.println("客户端文件位置："+remoteFile.getAbsolutePath()+"<br/>"); file1 = new File(this.getServletContext().getRealPath("attachment"),remoteFile.getName()); file1.getParentFile().mkdirs(); file1.createNewFile(); InputStream ins = fileItem.getInputStream(); OutputStream ous = new FileOutputStream(file1); try{ byte[] buffer = new byte[1024]; int len = 0; while((len = ins.read(buffer)) > -1) ous.write(buffer,0,len); out.println("以保存文件"+file1.getAbsolutePath()+"<br/>"); }finally{ ous.close(); ins.close(); } } if("file2".equals(fileItem.getFieldName())){ File remoteFile = new File(new String(fileItem.getName().getBytes(),"UTF-8")); out.println("遍历到file2...<br/>"); out.println("客户端文件位置："+remoteFile.getAbsolutePath()+"<br/>"); file2 = new File(this.getServletContext().getRealPath("attachment"),remoteFile.getName()); file2.getParentFile().mkdirs(); file2.createNewFile(); InputStream ins = fileItem.getInputStream(); OutputStream ous = new FileOutputStream(file2); try{ byte[] buffer = new byte[1024]; int len = 0; while((len = ins.read(buffer)) > -1) ous.write(buffer,0,len); out.println("以保存文件"+file2.getAbsolutePath()+"<br/>"); }finally{ ous.close(); ins.close(); } } } out.println("Request 解析完毕<br/><br/>"); } }catch(FileUploadException e){} out.println("<!DOCTYPE HTML PUBLIC /"-//W3C//DTD HTML 4.01 Transitional//EN/">"); out.println("<HTML>"); out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>"); out.println(" <BODY>"); if(file1 != null){ out.println("<div>"); out.println(" <div align='left'>file1;</div>"); out.println(" <div align='left'><a href='"+request.getContextPath()+"/attachment/"+ file1.getName()+"'target=_blank>"+file1.getName()+"</a>"); out.println("</div>"); out.println("</div>"); } if(file2 != null){ out.println("<div>"); out.println(" <div align='left'>file2;</div>"); out.println(" <div align='left'><a href='"+request.getContextPath()+"/attachment/"+ file2.getName()+"'target=_blank>"+file2.getName()+"</a>"); out.println("</div>"); out.println("</div>"); } out.println("<div>"); out.println(" <div align='left'>description1:</div>"); out.println(" <div align='left'>"); out.println(description1); out.println("</div>"); out.println("</div>"); out.println("<div>"); out.println(" <div align='left'>description2:</div>"); out.println(" <div align='left'>"); out.println(description2); out.println("</div>"); out.println("</div>"); out.println(" </BODY>"); out.println("</HTML>"); out.flush(); out.close(); } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here }}运行示例
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