java文件的上传

java使用apache commons-fileupload组件实现文件上传（控制文件上传的类型、文件上传的大小）
1.导入jar包（需要两个，idea中导入依赖，只需要导入common-fileupload，io会自动导入)
common-fileupload.jar

common-io.jar
2.jsp页面（样式省略）

<body><form action="UploadServlet" enctype="multipart/form-data" method="post">用户名：<input type="text" name="username" /><br> 上传文件：<input type="file" name="fileName" /><br> <input type="submit" value="文件上传" /><br> </form></body>

3.创建名为UploadServlet的Servlet，并在doPost()方法中编写实现代码，如下所示：

package com.upload.servlet;import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
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.FileUploadBase;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.IOUtils;/**
* Servlet implementation class UploadServlet
*/
public class UploadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;/*** @see HttpServlet#HttpServlet()*/
public UploadServlet() {super();// TODO Auto-generated constructor stub
}/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse*   response)*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// TODO Auto-generated method stubdoPost(request, response);
}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse*   response)*/
protected void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {// TODO Auto-generated method stubrequest.setCharacterEncoding("utf-8");// 设置响应编码// 得到上传文件的保存目录，将上传的文件存放于WEB-INF目录下，不允许外界直接访问，保证上传文件的安全String savePath = request.getServletContext().getRealPath("/WEB-INF/upload");// 上传时生成的临时文件保存目录String tempPath = request.getServletContext().getRealPath("/WEB-INF/temp");File tmpFile = new File(tempPath);if (!tmpFile.exists()) {// 创建临时目录tmpFile.mkdir();}// System.out.println("文件临时保存路径1:"+tempPath);// 1.创建磁盘工厂DiskFileItemFactory factory = new DiskFileItemFactory();factory.setSizeThreshold(1024 * 100);// 设置缓冲区的大小为100KB，如果不指定，那么缓冲区的大小默认是10KBfactory.setRepository(new File(tempPath));// 设置上传时文件的保存目录// 2.创建文件上传解析器ServletFileUpload upload = new ServletFileUpload(factory);// 设置允许上传文件的内存，这里设置为100KB，根据实际情况设置upload.setSizeMax(1024 * 100);// 3.判断提交上来的数据是否是上传表单的数据if (ServletFileUpload.isMultipartContent(request)) {try {// 4、使用ServletFileUpload解析器解析上传数据，解析结果返回的是一个List<FileItem>集合，每一个FileItem对应一个Form表单的输入项List<FileItem> list = upload.parseRequest(request);// 设置解析到的文件编码格式upload.setHeaderEncoding("utf-8");for (FileItem fileItem : list) {// 判断是否文件，结果为“true”就是普通表单，如果为“false”则是文件if (fileItem.isFormField()) {String fileName = fileItem.getFieldName();// 获得表单name属性名System.out.println(fileItem.getString("utf-8"));// 获取表单value值，并设定编码方式} else {String name = fileItem.getName();// 获取上传文件的名字// 限制上传文件的类型List<String> fileType = Arrays.asList("gif", "bmp", "jpg", "png");//允许上传文件的类型String fileExtName = name.substring(name.lastIndexOf(".") + 1);//获得文件的后缀名//System.out.println("上传文件的后缀名为:"+fileExtName);if (!fileType.contains(fileExtName)) {System.out.println("上传失败！文件类型只能是gif、bmp、jpg、png!");} else {InputStream input = fileItem.getInputStream();// 获得上传文件字节流// 创建输出文件String outPath = request.getServletContext().getRealPath(name);FileOutputStream output = new FileOutputStream(new File(outPath));// 使用IOUtils工具输出，也就是copy文件IOUtils.copy(input, output);System.out.println("上传成功！");System.out.println("保存的路径为：" + outPath);// 关闭输入流input.close();// 关闭输出流output.close();// 删除处理文件上传时生成的临时文件fileItem.delete();}}}} catch (FileUploadBase.SizeLimitExceededException e) {System.out.println("上传失败！上传的文件大小超出限制，最大只能上传"+upload.getSizeMax()+"bytes的文件");} catch (Exception e) {System.out.println("上传失败！");e.printStackTrace();}} else {// 如果不是文件上传类型，则采用普通表单获取方式request.setCharacterEncoding("UTF-8");String parameter = request.getParameter("username");System.out.println(parameter);}
}
}