使用Servlet处理一个上传的文件
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2024-02-25 23:22:27
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...
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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