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使用Servlet处理一个上传的文件

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) {
}

总结

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