使用Servlet处理一个上传的文件

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今天小编就为大家分享一篇关于使用Servlet处理一个上传的文件，小编觉得内容挺不错的，现在分享给大家，具有很好的参考价值，需要的朋友一起跟随小编来看看吧
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
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，谢谢大家对CodeAE代码之家的支持。如果你想了解更多相关内容请查看下面相关链接
原文链接：https://blog.csdn.net/sdr_zd/article/details/77952196

[Java] 使用Servlet处理一个上传的文件

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