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java下载功能,java下载功能怎么实现的

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怎样编一个能实现文件下载功能的JAVA程序

java实现文件下载

一、采用RequestDispatcher的方式进行

1、web.xml文件中增加

mime-mapping

extensiondoc/extension

mime-typeapplication/vnd.ms-word/mime-type

/mime-mapping

2、程序如下:

%@page language="java" import="java.net.*" pageEncoding="gb2312"%

%

response.setContentType("application/x-download");//设置为下载application/x-download

String filenamedownload = "/系统解决方案.doc";//即将下载的文件的相对路径

String filenamedisplay = "系统解决方案.doc";//下载文件时显示的文件保存名称

filenamedisplay = URLEncoder.encode(filenamedisplay,"UTF-8");

response.addHeader("Content-Disposition","attachment;filename=" + filenamedisplay);

try

{

RequestDispatcher dispatcher = application.getRequestDispatcher(filenamedownload);

if(dispatcher != null)

{

dispatcher.forward(request,response);

}

response.flushBuffer();

}

catch(Exception e)

{

e.printStackTrace();

}

finally

{

}

%

二、采用文件流输出的方式下载

1、web.xml文件中增加

mime-mapping

extensiondoc/extension

mime-typeapplication/vnd.ms-word/mime-type

/mime-mapping

2、程序如下:

%@page language="java" contentType="application/x-msdownload" import="java.io.*,java.net.*" pageEncoding="gb2312"%

%

//关于文件下载时采用文件流输出的方式处理:

//加上response.reset(),并且所有的%后面不要换行,包括最后一个;

//因为Application Server在处理编译jsp时对于%和%之间的内容一般是原样输出,而且默认是PrintWriter,

//而你却要进行流输出:ServletOutputStream,这样做相当于试图在Servlet中使用两种输出机制,

//就会发生:getOutputStream() has already been called for this response的错误

//详细请见《More Java Pitfill》一书的第二部分 Web层Item 33:试图在Servlet中使用两种输出机制 270

//而且如果有换行,对于文本文件没有什么问题,但是对于其它格式,比如AutoCAD、Word、Excel等文件

//下载下来的文件中就会多出一些换行符0x0d和0x0a,这样可能导致某些格式的文件无法打开,有些也可以正常打开。

response.reset();//可以加也可以不加

response.setContentType("application/x-download");//设置为下载application/x-download

// /../../退WEB-INF/classes两级到应用的根目录下去,注意Tomcat与WebLogic下面这一句得到的路径不同,WebLogic中路径最后没有/

System.out.println(this.getClass().getClassLoader().getResource("/").getPath());

String filenamedownload = this.getClass().getClassLoader().getResource("/").getPath() + "/../../系统解决方案.doc";

String filenamedisplay = "系统解决方案.doc";//系统解决方案.txt

filenamedisplay = URLEncoder.encode(filenamedisplay,"UTF-8");

response.addHeader("Content-Disposition","attachment;filename=" + filenamedisplay);

OutputStream output = null;

FileInputStream fis = null;

try

{

output = response.getOutputStream();

fis = new FileInputStream(filenamedownload);

byte[] b = new byte[1024];

int i = 0;

while((i = fis.read(b)) 0)

{

output.write(b, 0, i);

}

output.flush();

}

catch(Exception e)

{

System.out.println("Error!");

e.printStackTrace();

}

finally

{

if(fis != null)

{

java下载功能实现

楼主得在后台的控制器中用reponse的输出流转化一下,我给你个例子。

InputStream fis = new BufferedInputStream(new FileInputStream(filePath));byte[] buffer = new byte[fis.available()];fis.read(buffer);fis.close();response.reset();response.addHeader("Content-Disposition", "attachment;filename=" + new String(fileName.getBytes("gbk"),"ISO-8859-1"));response.addHeader("Content-Length", "" + excelFile.length());OutputStream toClient = new BufferedOutputStream(response.getOutputStream());response.setContentType("application/octet-stream");toClient.write(buffer);toClient.flush();toClient.close();

求采纳为满意回答。

java 如何实现下载功能

import java.io.File;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.ProtocolException;

import java.net.URI;

import java.net.URL;

import java.util.Random;

/**

*

* 实现了下载的功能*/

public class SimpleTh {

public static void main(String[] args){

// TODO Auto-generated method stub

//String path = "倩女幽魂.mp3";//MP3下载的地址

String path ="";

try {

new SimpleTh().download(path, 3); //对象调用下载的方法

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

}

public static String getFilename(String path){//获得文件的名字

return path.substring(path.lastIndexOf('/')+1);

}

public void download(String path,int threadsize) throws Exception//下载的方法

{//参数 下载地址,线程数量

URL url = new URL(path);

HttpURLConnection conn = (HttpURLConnection)url.openConnection();//获取HttpURLConnection对象

conn.setRequestMethod("GET");//设置请求格式,这里是GET格式

conn.setReadTimeout(5*1000);//

int filelength = conn.getContentLength();//获取要下载文件的长度

String filename = getFilename(path);

File saveFile = new File(filename);

RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");

accessFile.setLength(filelength);

accessFile.close();

int block = filelength%threadsize ==0?filelength/threadsize:filelength/threadsize+1;

for(int threadid = 0;threadid=threadsize;threadid++){

new DownloadThread(url,saveFile,block,threadid).start();

}

}

private final class DownloadThread extends Thread{

private URL url;

private File saveFile;

private int block;//每条线程下载的长度

private int threadid;//线程id

public DownloadThread(URL url,File saveFile,int block,int threadid){

this.url = url;

this.saveFile= saveFile;

this.block = block;

this.threadid = threadid;

}

@Override

public void run() {

//计算开始位置的公式:线程id*每条线程下载的数据长度=?

//计算结束位置的公式:(线程id+1)*每条线程下载数据长度-1=?

int startposition = threadid*block;

int endposition = (threadid+1)*block-1;

try {

try {

RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");

accessFile.seek(startposition);//设置从什么位置写入数据

HttpURLConnection conn = (HttpURLConnection)url.openConnection();

conn.setRequestMethod("GET");

conn.setReadTimeout(5*1000);

conn.setRequestProperty("Range","bytes= "+startposition+"-"+endposition);

InputStream inStream = conn.getInputStream();

byte[]buffer = new byte[1024];

int len = 0;

while((len = inStream.read(buffer))!=-1){

accessFile.write(buffer, 0, len);

}

inStream.close();

accessFile.close();

System.out.println("线程id:"+threadid+"下载完成");

} catch (FileNotFoundException e) {

e.printStackTrace();

}

} catch (IOException e) {

e.printStackTrace();

}

}

}

}

参考一下这个代码。

java如何实现文件上传和下载的功能

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.jspsmart.upload.*;

import net.sf.json.JSONObject;

import action.StudentAction;

public class UploadServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

this.doPost(request, response);

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

boolean result=true;

SmartUpload mySmartUpload=new SmartUpload();

mySmartUpload.initialize(this.getServletConfig(), request,response);

mySmartUpload.setTotalMaxFileSize(50*1024*1024);//大小限制

mySmartUpload.setAllowedFilesList("doc,docx");//后缀名限制

try {

mySmartUpload.upload();

com.jspsmart.upload.File myFile = mySmartUpload.getFiles().getFile(0);

myFile.saveAs("/file/"+1+".doc");//保存目录

} catch (SmartUploadException e) {

e.printStackTrace();result=false;

}

//*****************************//

response.setContentType("text/html;charset=UTF-8");

response.setHeader("Cache-Control","no-cache");

PrintWriter out = response.getWriter();

out.print(result);

out.flush();

out.close();

}

}

//我这是ajax方式的,不想这样,把//**********************//以下部分修改就行了

//需要SmartUpload组件,去网上下个就行了,也有介绍的

Java如何利用url下载MP3保存到本地?

Java如何利用url下载MP3保存的方法:

1 /** ;

2      * TODO 下载文件到本地 ;

3      * @author nadim  ;

4      * @date Sep 11, 2015 11:45:31 AM ;

5      * @param fileUrl 远程地址 ;

6      * @param fileLocal 本地路径 ;

7      * @throws Exception ;

8      */ ;

9     public void downloadFile(String fileUrl,String fileLocal) throws Exception {;

10         URL url = new URL(fileUrl);

11         HttpURLConnection urlCon = (HttpURLConnection) url.openConnection();

12         urlCon.setConnectTimeout(6000);

13         urlCon.setReadTimeout(6000);

14         int code = urlCon.getResponseCode();

15         if (code != HttpURLConnection.HTTP_OK) {

16             throw new Exception("文件读取失败");

17         }      

18         //读文件流;

19        DataInputStream in = new DataInputStream(urlCon.getInputStream());

20         DataOutputStream out = new DataOutputStream(new FileOutputStream(fileLocal));

21         byte[] buffer = new byte[2048];

22         int count = 0;

23         while ((count = in.read(buffer)) 0) {;

24             out.write(buffer, 0, count);

25         }

26         out.close();

27         in.close();

28     }。

Java是一门面向对象编程语言,不仅吸收了C++语言的各种优点,还摒弃了C++里难以理解的多继承、指针等概念,因此Java语言具有功能强大和简单易用两个特征。

Java语言作为静态面向对象编程语言的代表,极好地实现了面向对象理论,允许程序员以优雅的思维方式进行复杂的编程 。

java怎样实现数据下载功能呢

这是我以前弄的一个下载的模块,里面的pl指的是System.out.println(),

详情可以看 ;tid=156

package com.jc.download;

import java.io.BufferedInputStream;

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import static com.jc.tool.io.Out.pl;

public class DownloadThread extends Thread {

private String url = null;

private String file = null;

private long offset = 0;

private long length = 0;

private int no = 0;

public DownloadThread(String url, String file, long offset, long length) {

pl("正在初始化下载线程...");

this.url = url;

this.file = file;

this.offset = offset;

this.length = length;

}

public void setNo(int no) {

this.no = no;

}

@Override

public void run() {

try {

pl("线程【"+no+"】开始连接主机...");

HttpURLConnection conn = (HttpURLConnection) new URL(url)

.openConnection();

pl("线程【"+no+"】发送下载请求...");

conn.setRequestMethod("GET");

conn.setRequestProperty("RANGE", "bytes=" + this.offset + "-"

+ (this.offset + this.length - 1));

pl("线程【"+no+"】创建文件流...");

BufferedInputStream bis = new BufferedInputStream(

conn.getInputStream());

byte[] buf = new byte[1024];

int bytesRead;

pl("线程【"+no+"】开始向文件写入数据...");

while ((bytesRead = bis.read(buf, 0, buf.length)) != -1) {

this.writeFile(file, offset, buf, bytesRead);

this.offset += bytesRead;

}

pl("线程【"+no+"】写入完成");

} catch (IOException e) {

e.printStackTrace();

}

pl("线程【"+no+"】退出");

}

public void writeFile(String fileName, long offset, byte[] bytes,

int realLength) throws IOException {

File file = new File(fileName);

RandomAccessFile raf = new RandomAccessFile(file, "rw");

raf.seek(offset);

raf.write(bytes, 0, realLength);

raf.close();

}

}