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文件上传和下载功能是Java Web必备技能，很实用。
本文使用的是Apache下的著名的文件上传组件
org.apache.commons.fileupload 实现
下面结合最近看到的一些资料以及自己的尝试，先写第一篇文件上传。后续会逐步实现下载，展示文件列表，上传信息持久化等。
废话少说，直接上代码
第一步、引用jar包，设置上传目录
commons-fileupload-1.3.1.jar
commons-io-2.4.jar
上传目录：WEB-INF/tempFiles和WEB-INF/uploadFiles
第二步、编写JSP页面
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<title>文件上传测试</title>
</head>
<body>
<form method="POST" enctype="multipart/form-data" action="<%=request.getContextPath()%>/UploadServlet">
文件: <input type="file" name="upfile"><br/>
<br/>
<input type="submit" value="上传">
</form>
<c:if test="${not empty errorMessage}">
<input type="text" value="${errorMessage}" style="color:red;" disabled="disabled">
</c:if>
</body>
</html>
第三步、编写Servlet，处理文件上传的核心
package servlet;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadBase;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.ProgressListener;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Calendar;
import java.util.Iterator;
import java.util.List;
import java.util.UUID;
/**
* 处理文件上传
*
* @author xusucheng
* @create 2017-12-27
**/
@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//设置文件上传基本路径
String savePath = this.getServletContext().getRealPath("/WEB-INF/uploadFiles");
//设置临时文件路径
String tempPath = this.getServletContext().getRealPath("/WEB-INF/tempFiles");
File tempFile = new File(tempPath);
if (!tempFile.exists()) {
tempFile.mkdir();
}
//定义异常消息
String errorMessage = "";
//创建file items工厂
DiskFileItemFactory factory = new DiskFileItemFactory();
//设置缓冲区大小
factory.setSizeThreshold(1024 * 100);
//设置临时文件路径
factory.setRepository(tempFile);
//创建文件上传处理器
ServletFileUpload upload = new ServletFileUpload(factory);
//监听文件上传进度
ProgressListener progressListener = new ProgressListener() {
public void update(long pBytesRead, long pContentLength, int pItems) {
System.out.println("正在读取文件： " + pItems);
if (pContentLength == -1) {
System.out.println("已读取： " + pBytesRead + " 剩余0");
} else {
System.out.println("文件总大小：" + pContentLength + " 已读取：" + pBytesRead);
}
}
};
upload.setProgressListener(progressListener);
//解决上传文件名的中文乱码
upload.setHeaderEncoding("UTF-8");
//判断提交上来的数据是否是上传表单的数据
if (!ServletFileUpload.isMultipartContent(request)) {
//按照传统方式获取数据
return;
}
//设置上传单个文件的大小的最大值，目前是设置为1024*1024字节，也就是1MB
upload.setFileSizeMax(1024 * 1024);
//设置上传文件总量的最大值，最大值=同时上传的多个文件的大小的最大值的和，目前设置为10MB
upload.setSizeMax(1024 * 1024 * 10);
try {
//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> items = upload.parseRequest(request);
Iterator<FileItem> iterator = items.iterator();
while (iterator.hasNext()) {
FileItem item = iterator.next();
//判断jsp提交过来的是不是文件
if (item.isFormField()) {
errorMessage = "请提交文件！";
break;
} else {
//文件名
String fileName = item.getName();
if (fileName == null || fileName.trim() == "") {
System.out.println("文件名为空！");
}
//处理不同浏览器提交的文件名带路径问题
fileName = fileName.substring(fileName.lastIndexOf("\\") + 1);
//文件扩展名
String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1);
//判断扩展名是否合法
if (!validExtension(fileExtension)) {
errorMessage = "上传文件非法！";
item.delete();
break;
}
//获得文件输入流
InputStream in = item.getInputStream();
//得到保存文件的名称
String saveFileName = createFileName(fileName);
//得到文件保存路径
String realFilePath = createRealFilePath(savePath, saveFileName);
//创建文件输出流
FileOutputStream out = new FileOutputStream(realFilePath);
//创建缓冲区
byte buffer[] = new byte[1024];
int len = 0;
while ((len = in.read(buffer)) > 0) {
//写文件
out.write(buffer, 0, len);
}
//关闭输入流
in.close();
//关闭输出流
out.close();
//删除临时文件 TODO
item.delete();
//将上传文件信息保存到附件表中 TODO
}
}
} catch (FileUploadBase.FileSizeLimitExceededException e) {
e.printStackTrace();
request.setAttribute("errorMessage", "单个文件超出最大值！！！");
request.getRequestDispatcher("pages/upload/upload.jsp").forward(request, response);
return;
} catch (FileUploadBase.SizeLimitExceededException e) {
e.printStackTrace();
request.setAttribute("errorMessage", "上传文件的总的大小超出限制的最大值！！！");
request.getRequestDispatcher("pages/upload/upload.jsp").forward(request, response);
return;
} catch (FileUploadException e) {
e.printStackTrace();
request.setAttribute("errorMessage", "文件上传失败！！！");
request.getRequestDispatcher("pages/upload/upload.jsp").forward(request, response);
return;
}
request.setAttribute("errorMessage", errorMessage);
request.getRequestDispatcher("pages/upload/upload.jsp").forward(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
private boolean validExtension(String fileExtension) {
String[] exts = {"jpg", "txt", "doc", "pdf"};
for (int i = 0; i < exts.length; i++) {
if (fileExtension.equals(exts[i])) {
return true;
}
}
return false;
}
private String createFileName(String fileName) {
return UUID.randomUUID().toString() + "_" + fileName;
}
/**
* 根据基本路径和文件名称生成真实文件路径，基本路径\\年\\月\\fileName
*
* @param basePath
* @param fileName
* @return
*/
private String createRealFilePath(String basePath, String fileName) {
Calendar today = Calendar.getInstance();
String year = String.valueOf(today.get(Calendar.YEAR));
String month = String.valueOf(today.get(Calendar.MONTH) + 1);
String upPath = basePath + File.separator + year + File.separator + month + File.separator;
File uploadFolder = new File(upPath);
if (!uploadFolder.exists()) {
uploadFolder.mkdirs();
}
String realFilePath = upPath + fileName;
return realFilePath;
}
}
第四步、测试
http://localhost:8080/helloweb/pages/upload/upload.jsp
