Servlet处理一个上传的文件

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Servlet中可以使用post请求上传文件，使用getReader()和getInputStream()自己处理，也可以使用getPart()或getParts()封装了一些功能的方法处理，getParts()可以同时上传多个文件。接下来使用四个Demo来练习一下使用方法

一.使用getReader()和getInputStream()

Demo1

<!-- 这是HTML代码块，窗体网页上显示的是一个选择文件的input框和一个upload的button --><!DOCTYPE html><html>    <head>        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">        <title></title>    </head>    <body>        <form action="upload" method="post" enctype="multipart/form-data">        选择文件：<input type="file" name="filename" value="" /><br>        <input type="submit" value="Upload" name="upload" />        </form>    </body></html>

/* * 这是Servlet处理部分 */import java.io.DataInputStream;import java.io.FileOutputStream;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class uploadServlet */@WebServlet("/upload")public class UploadServlet extends HttpServlet {    private static final long serialVersionUID = 1L;    /**     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)     */    protected void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        //读取请求Body        byte[] body = readBody(request);        //取得所有Body内容的字符串表示        String textBody = new String(body, "ISO-8859-1");        //取得上传的文件的文件名(取得路径并分离)        String filename = getFilename(textBody);        //取得文件内容在Body中的首尾索引        Position p = getFilePosition(request, textBody);        //将内容输出到文件        writeTo(filename, body, p);    }    //存放索引的类    class Position{        int begin;        int end;        Position(int begin, int end) {            this.begin = begin;            this.end = end;        }    }    //读取请求body    private byte[] readBody(HttpServletRequest request) throws IOException {        int formDataLength = request.getContentLength();        //获得ServletInputStream对象        //getReader()和getInputStream()只能则一调用，否则会抛出IllegalStateException异常        DataInputStream dataStream = new DataInputStream(request.getInputStream());        byte[] body = new byte[formDataLength];        int totalBytes = 0;        while(totalBytes < formDataLength) {            int bytes = dataStream.read(body, totalBytes, formDataLength);            totalBytes += bytes;        }        return body;    }    //取得上传文件名称    private String getFilename(String reqBody) {        //获取filename的value,10是filename="的长度        //通过后台调试我发现filename=后加的是带着双引号的路径名，在获取路径名时不需要分号所以在分离时就将分号也分离掉了        String filename = reqBody.substring(reqBody.indexOf("filename=\"") + 10);        //找到文件名这行的末尾，过滤掉对于获取文件名而言的无用信息        filename = filename.substring(0, filename.indexOf("\n"));        //获取不包含路径名的文件名        filename =  filename.substring(filename.lastIndexOf("\\") + 1, filename.lastIndexOf("\""));        //此时后台打印分离路径后的文件名并将其作为返回值返回        System.out.println(filename);        return filename;    }    //取得文件开始和结束位置    private Position getFilePosition(HttpServletRequest request, String textBody) throws IOException {        /*         * 取得文件区段边界信息         */        String contentType = request.getContentType();        String boundaryText = contentType.substring(                contentType.lastIndexOf("=") + 1, contentType.length());        /*         * 取得实际上传文件的起始与结束位置         */        int pos = textBody.indexOf("filename=\"");        pos = textBody.indexOf("\n", pos) + 1;        pos = textBody.indexOf("\n", pos) + 1;        pos = textBody.indexOf("\n", pos) + 1;        int boundaryLoc = textBody.indexOf(boundaryText, pos) - 4;        int begin = ((textBody.substring(0, pos)).getBytes("ISO-8859-1")).length;        int end = ((textBody.substring(0, boundaryLoc)).getBytes("ISO-8859-1")).length;        return new Position(begin, end);    }    //输出至文件    private void writeTo(String filename, byte[] body, Position p) throws IOException {        //默认上传的文件是在F:\\javaeeAroundFiles目录下        FileOutputStream fos = new FileOutputStream("F:\\javaeeAroundFiles\\later\\" + filename);        fos.write(body, p.begin, (p.end - p.begin));        fos.flush();        fos.close();    }}

二.使用getPart()和getInputStream()

Demo2

//HTML代码块<!-- 该HTML供uploadPartDemo和uploadPartDemo2共同使用，使用时通过更改body的form的action属性值控制 --><!DOCTYPE html><html>    <head>        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">        <title></title>    </head>    <body>        <form action="uploadPhoto" method="post"        enctype="multipart/form-data">        上传相片：<input type="file" name="photo" /><br><br>        <input type="submit" value="上传" name="upload" />        </form>    </body></html>

/* uploadPhotoDemo.java */import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import javax.servlet.ServletException;import javax.servlet.annotation.MultipartConfig;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.Part;/** * Servlet implementation class uploadPartDemo *///Tomcat中必须设置@MutipartConfig标注才能使用getPart()相关API@MultipartConfig@WebServlet("/uploadPhoto")public class uploadPartDemo extends HttpServlet {    private static final long serialVersionUID = 1L;    /**     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)     */    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        //getPart()获取Part对象        Part part = request.getPart("photo");        String filename = getFilename(part);        writeTo(filename, part);    }    private String getFilename(Part part) {        String header = part.getHeader("Content-Disposition");        //获取完整路径        String filename = header.substring(header.indexOf("filename=\"") + 10, header.lastIndexOf("\""));        //filename after substring is: F:\Entertainment\pictures\e5e893df874df44d99f06bc52504a65c.jpg        System.out.println("filename after substring is: " + filename);        //获取文件名        filename = filename.substring(filename.lastIndexOf("\\") + 1);        //filename after 2 substring is: e5e893df874df44d99f06bc52504a65c.jpg        System.out.println("filename after 2 substring is: " + filename);        return filename;    }    private void writeTo(String filename, Part part) throws IOException, FileNotFoundException {        InputStream is = part.getInputStream();        FileOutputStream fos = new FileOutputStream("F:\\javaeeAroundFiles\\later\\" + filename);        byte[] buffer = new byte[1024];        int length = -1;        while((length = is.read(buffer)) != -1) {            fos.write(buffer, 0, length);        }        is.close();        fos.close();    }}

这个Demo和第一个代码最大的区别就是，通过getPart()方法获得了Part对象，通过part对象的getHeader()方法指定标头获得对应的值。
在Tomcat中要在Servlet上设置@MultipartConfig才能取得Part对象，否则getPart会得到null
@MultipartConfig含有的属性如下：

fileSizeThreshold：整数值设置，若上传文件大小超过设置门槛，则先写入缓存文件，默认值为0
location：字符串设置，设置写入文件时的目录，使用时与write方法一起使用，下一个Demo中演示如何使用，默认是空字符串
maxFileSize：限制上传文件大小，默认-1L即无限制
maxRequestSize：限制multipart/form-data请求个数，默认值为-1L

Demo3

使用Part的write方法进行文件的写入，HTML文件查看Demo2注释部分

/* uploadPhotoDemo2.java */import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.MultipartConfig;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.Part;/** * Servlet implementation class uploadPartDemo2 */ //设置属性，这里的最后一级不用分隔符，可以与Demo2中writeTo方法的路径做一下对比@MultipartConfig(location="F:\\javaeeAroundFiles\\later")@WebServlet("/uploadPhoto2")public class uploadPartDemo2 extends HttpServlet {    private static final long serialVersionUID = 1L;    /**     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)     */    protected void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        //文件名中可能有中文字符所以进行编码设置，使用setCharacterEncoding()方法        request.setCharacterEncoding("UTF-8");        Part part = request.getPart("photo");        String filename = getFilename(part);        //使用Part的write方法，写入location指定路径        part.write(filename);    }    //获取文件名与Demo2相同不放代码    private String getFilename(Part part) {}}

若要实现同时上传多个文件则可以使用getParts()方法，获取到的Part对象被保存在一个Collection中

Demo4

<!-- 该HTML是三个input选框，选择三个文件 --><!DOCTYPE html><html>    <head>        <meta http-equiv="Content-Type"                content="text/html; charset=UTF-8">        <title></title>    </head>    <body>        <form action="uploadParts" method="post"            enctype="multipart/form-data">            文件1：<input type="file" name="file1" value="" /><br>            文件2：<input type="file" name="file2" value="" /><br>            文件3：<input type="file" name="file3" value="" /><br><br>            <input type="submit" value="上传" name="upload" />        </form>    </body></html>

import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.MultipartConfig;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.Part;/** * Servlet implementation class uploadPartsDemo */@MultipartConfig(location="F:\\javaeeAroundFiles\\later")@WebServlet("/uploadParts")public class uploadPartsDemo extends HttpServlet {    private static final long serialVersionUID = 1L;    /**     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)     */    protected void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        request.setCharacterEncoding("UTF-8");        //使用foreach遍历获取每一个Part对象        for(Part part : request.getParts()) {            if(part.getName().startsWith("file")) {                String filename = getFilename(part);                part.write(filename);            }        }    }    //与之前的getFilename()方法相同    private String getFilename(Part part) {}

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