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.javaimport 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.javaimport 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) {} 总结
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