使用Servlet处理一个上传的文件

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

选择文件：

//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(http://"\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

enctype="multipart/form-data">

上传相片：

//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 rhttp://esponse) 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

content="text/html; charset=UTF-8">

enctype="multipart/form-data">

文件1：

文件2：

文件3：

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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