servlet 3.0实现文件上传文件

http请求头 content-type常见的值有，x-www-form-urlencoded,multipart/form-data,application/json三种 ，servlet对这三种类型的请求有不同的处理方式。

servlet3.0需要tomcat7+,jdk1.6+支持。

package cn.xxx;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.*;
import java.util.Collection;
import java.util.Enumeration;

/**
 * 默认的content-type是content-type=application/x-www-form-urlencoded
 * 上传文件时，content-type必须是: multipart/form-data,等,multipart类型，本质是通过流的形式上传
 */

@MultipartConfig
public class FileUploadServlet extends HttpServlet {

    /**
     * 处理所有POST请求
     *
     * @param request
     * @param response
     * @throws javax.servlet.ServletException
     * @throws IOException
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        // 打印所有请求头
        printAllHeaders(request, response);
        // 打印所有请求参数,form中，
        printAllparames(request, response);
        String contentType = request.getHeader("content-type");
        if ("application/json".equals(contentType)) {
            handleJsonRequest(request, response);
        } else if (null != contentType && contentType.contains("multipart")) {
            // 处理Mutipart请求
            handleMutipartRequest(request, response);
        } else {
            handleNonMutipartRequest(request, response);
        }
        PrintWriter out = response.getWriter();
        out.write("success!");
        out.flush();
        out.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException {
        doPost(request, response);
    }

    /**
     * 打印所有请求头
     *
     * @param request
     * @param response
     */
    private void printAllHeaders(HttpServletRequest request, HttpServletResponse response) {
        Enumeration<String> hNames = request.getHeaderNames();
        String headerName = null;
        while (hNames.hasMoreElements()) {
            headerName = hNames.nextElement();
            System.out.println(headerName + "=" + request.getHeader(headerName));
        }
        System.out.println("=====以上是request的所有header=====");
    }

    /**
     * 打印所有请求参数
     *
     * @param request
     * @param response
     */
    private void printAllparames(HttpServletRequest request, HttpServletResponse response) {
        Enumeration<String> parameterNames = request.getParameterNames();
        String paramName = null;
        while (parameterNames.hasMoreElements()) {
            paramName = parameterNames.nextElement();
            System.out.println(paramName + "=" + request.getParameter(paramName));
        }
        System.out.println("=====以上是request的所有Parameter=====");
        // 结论： 除file的值外，其它的的值是可以通过.request.getParameter("name"); 获取的
    }


    private void handleNonMutipartRequest(HttpServletRequest request, HttpServletResponse response) {
        System.out.println("没有multipart...");
    }

    /**
     * 处理multipart请求
     *
     * @param request
     * @param response
     * @throws IOException
     * @throws ServletException
     */
    private void handleMutipartRequest(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        // 如果haader中Content-Type属性没有，mutipart/form-data等mutipar类型的值的话，调用request.getParts()这个方法会报错。
        Collection<Part> parts = request.getParts();

        // 读取所有文件
        for (Part part : parts) {

            //  part = request.getPart("myfile"); ，根据part 的Name 获得指定part，
            // partName 与表单中的name属性一致:如<input type="file" name="myfile">
            System.out.println("当前part的名字是：" + part.getName());

            /**********  测试Part对象带有哪些header属性:开始**********/
            Collection<String> headerNames = part.getHeaderNames();
            for (String name : headerNames) {
                System.out.println(name + "=" + part.getHeader(name));
            }
            /**
             *  结果一：
             *  content-type=image/png
             *  content-disposition=form-data; name="myfile"; filename="102247307079625130.png"
             *  结果二：
             *  content-type=text/plain
             *  content-disposition=form-data; name="myfile"; filename="idea 快捷键.txt"
             *  结果三：
             *  content-disposition=form-data; name="id"
             *  结论：file类型的Part的header有两个属性
             *       content-type是选择的文件的类型
             *       content-disposition是文件名及form表单中name名字
             *       如果不是file类型的input，是没有content-type属性的
             */
            /********** 测试Part对象带有哪些header属性:结束***********/

            String contentDisposition = part.getHeader("content-disposition");
            // 区分file和其它input
            if (contentDisposition != null && contentDisposition.contains("filename")) {
                //System.out.println(contentDisposition);
                // 保存文件到指定目录
                part.write("D:\" + getFileName(contentDisposition));
                System.out.println("文件已经保存到:" + "D:\" + getFileName(contentDisposition));
            } else {
                InputStream is = part.getInputStream();
                byte[] b = new byte[1024];
                int a = is.read(b);
                System.out.println(part.getName() + "=" + new String(b));
                is.close();
            }
        }
    }

    private void handleJsonRequest(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        ServletInputStream servletInputStream = request.getInputStream();
        BufferedReader br = new BufferedReader(new InputStreamReader(servletInputStream));
        StringBuffer stringBuffer = new StringBuffer();
        String strLine = null;
        while ((strLine = br.readLine()) != null) {
            stringBuffer.append(strLine);
        }
        System.out.println("jsonData:::" + stringBuffer);
        servletInputStream.close();
        br.close();
    }

    /**
     * 从content-disposition中解析出文件名称
     *
     * @param contentDisposition
     * @return
     */
    private String getFileName(String contentDisposition) {
        String[] strs1 = contentDisposition.split(";");
        String fileName = strs1[2].split("=")[1];
        return fileName.replaceAll(""", "");
    }
}

web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
         xmlns="http://java.sun.com/xml/ns/j2ee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

    <servlet>
        <servlet-name>FileUploadServlet</servlet-name>
        <servlet-class>cn.mamp.FileUploadServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FileUploadServlet</servlet-name>
        <url-pattern>/up</url-pattern>
    </servlet-mapping>
</web-app>

pom.xml依赖

<dependencies>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

 测试页面

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<!--file和其它表单元素混合-->
<form action="http://localhost:8090/web/up" method="post" enctype="multipart/form-data">
    <input type="file" name="myfile">
    <input type="text" name="id">
    <input type="text" name="name">
    <input type="submit" value="submit">
</form>
<!--多个file元素-->
<form action="http://localhost:8090/web/up" method="post" enctype="multipart/form-data">
    <input type="file" name="myfile1">
    <input type="file" name="myfile2">
    <input type="submit" value="submit">
</form>
<!--没有file元素-->
<form action="http://localhost:8090/web/up" method="post">
    <input type="text" name="id">
    <input type="text" name="name">
    <input type="submit" value="submit">
</form>

</body>
</html>