### 文件上传下载
- 文件上传
- 客户端
1、input 的 type 设置为 file。
2、form 表单的 method 设置为 post（get 会将文件名传给后台，而非文件本身）
3、form 表单的 enctype 设置为 multipart/form-data （以二进制的形式传输数据）
- 服务端
commons-fileupload,commons-io
基本思想：commons-fileupload 可以解析请求，得到一个泛型为 FileItem 的集合。
commons-fileupload 可以将所有的请求信息都解析成 FileItem 对象，无论是表单域还是文件域。
开发者就可以对 FileItem 集合进行操作，从而完成上传。
上传组件可以将传来的二进制数据解析成一个集合，进而方便开发。
```jsp
<%--
Created by IntelliJ IDEA.
User: southwind
Date: 2019-07-28
Time: 20:16
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<form action="/upload.do" enctype="multipart/form-data" method="post">
<input type="file" name="img"/>
<input type="text" name="desc"/>
<input type="submit" value="上传"/>
</form>
</body>
</html>
```
```java
package com.southwind.controller;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
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.*;
import java.util.List;
@WebServlet("/upload.do")
public class UploadServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException {
//创建DiskFileItemFactory
DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
//创建文件解析器
ServletFileUpload upload = new ServletFileUpload(fileItemFactory);
//获取FileItem集合
try {
List<FileItem> list = upload.parseRequest(req);
//遍历list
for (FileItem fileItem:list){
if(!fileItem.isFormField()){
String fileName = fileItem.getName();
try {
InputStream inputStream = fileItem.getInputStream();
String path = req.getServletContext().getRealPath("");
OutputStream outputStream = new FileOutputStream(path+"/files/"+fileName);
int temp = 0;
while((temp=inputStream.read())!=-1){
outputStream.write(temp);
}
inputStream.close();
outputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
} catch (FileUploadException e) {
e.printStackTrace();
}
}
}
```
- 文件下载
```jsp
<%--
Created by IntelliJ IDEA.
User: southwind
Date: 2019-07-28
Time: 21:43
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<a href="/download.do">1.png</a>
</body>
</html>
```
```java
package com.southwind.controller;
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.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
@WebServlet("/download.do")
public class DownloadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("application/x-msdownload");
String fileName = "1.png";
resp.setHeader("Content-Disposition","attachment;filename="+fileName);
OutputStream outputStream = resp.getOutputStream();
String path = req.getServletContext().getRealPath("")+"/files/"+fileName;
InputStream inputStream = new FileInputStream(path);
int temp = 0;
while((temp = inputStream.read())!=-1){
outputStream.write(temp);
}
outputStream.close();
inputStream.close();
}
}
```
download.jsp
<%-- Created by IntelliJ IDEA. User: southwind Date: 2019-07-28 Time: 21:43 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <a href="/download.do">1.png</a> <a href="/download.do">1.png</a> </body> </html>
upload.jsp
<%-- Created by IntelliJ IDEA. User: southwind Date: 2019-07-28 Time: 20:16 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>Title</title> </head> <body> <form action="/upload.do" enctype="multipart/form-data" method="post"> <input type="file" name="img"/> <input type="text" name="desc"/> <input type="submit" value="上传"/> </form> </body> </html>
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> </web-app>
DownloadServlet.java
package com.southwind.controller; 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.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; @WebServlet("/download.do") public class DownloadServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String name = req.getParameter("name"); resp.setContentType("application/x-msdownload"); String fileName = "1.png"; resp.setHeader("Content-Disposition","attachment;filename="+fileName); OutputStream outputStream = resp.getOutputStream(); String path = req.getServletContext().getRealPath("")+"/files/"+fileName; InputStream inputStream = new FileInputStream(path); int temp = 0; while((temp = inputStream.read())!=-1){ outputStream.write(temp); } outputStream.close(); inputStream.close(); } }
UploadServlet.java
package com.southwind.controller; import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.FileUploadException; 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.*; import java.util.List; @WebServlet("/upload.do") public class UploadServlet extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException { //创建DiskFileItemFactory DiskFileItemFactory fileItemFactory = new DiskFileItemFactory(); //创建文件解析器 ServletFileUpload upload = new ServletFileUpload(fileItemFactory); //获取FileItem集合 try { List<FileItem> list = upload.parseRequest(req); //遍历list for (FileItem fileItem:list){ if(!fileItem.isFormField()){ String fileName = fileItem.getName(); try { InputStream inputStream = fileItem.getInputStream(); String path = req.getServletContext().getRealPath(""); OutputStream outputStream = new FileOutputStream(path+"/files/"+fileName); int temp = 0; while((temp=inputStream.read())!=-1){ outputStream.write(temp); } inputStream.close(); outputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } catch (FileUploadException e) { e.printStackTrace(); } } }