A. javaweb中的文件下载实现
需要在响复应头部加上一制些标示，告诉浏览器这个是文件下载。如果你用了框架比如struts，需要加如下配置<result name="success" type="stream"> <param name="contentType">application/octet-stream;charset=ISO8859-1</param> <param name="inputName">fileStream</param> <param name="contentDisposition">attachment;filename="${fileName}"</param> <param name="bufferSize">2048</param> </result>如果没有用框架，就手动在返回对象添加这些contentType
B. 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
C. 通过java实现文件下载
在jsp/servlet中断点/多线程下载文件<%@ page import="java.io.File" %><%@ page import="java.io.IOException" %><%@ page import="java.io.OutputStream" %><%@ page import="java.io.RandomAccessFile" %><%! public void downloadFile(HttpServletRequest request, HttpServletResponse response, File file) throws IOException { RandomAccessFile raf = new RandomAccessFile(file, "r"); java.io.FileInputStream fis = new java.io.FileInputStream(raf.getFD()); response.setHeader("Server", "www.trydone.com"); response.setHeader("Accept-Ranges", "bytes"); long pos = 0; long len; len = raf.length(); if (request.getHeader("Range") != null) { response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); pos = Long.parseLong(request.getHeader("Range") .replaceAll("bytes=", "") .replaceAll("-", "") ); } response.setHeader("Content-Length", Long.toString(len – pos)); if (pos != 0) { response.setHeader("Content-Range", new StringBuffer() .append("bytes ") .append(pos) .append("-") .append(Long.toString(len – 1)) .append("/") .append(len) .toString() ); } response.setContentType("application/octet-stream"); response.setHeader("Content-Disposition", new StringBuffer() .append("attachment;filename=\"") .append(file.getName()) .append("\"").toString()); raf.seek(pos); byte[] b = new byte[2048]; int i; OutputStream outs = response.getOutputStream(); while ((i = raf.read(b)) != -1) { outs.write(b, 0, i); } raf.close(); fis.close(); }%><% String filePath = request.getParameter("file"); filePath = application.getRealPath(filePath); File file = new File(filePath); downloadFile(request, response, file);%>是否可以解决您的问题？
D. java 下载功能
下载功能实际上就是将远程服务器的文件流通过ftp功能转换为本地文件流进行存储。举例： /** *下载并解压文件 * * @param localFilePath * @param fileName * @param routeFilepath * @return * @throws Exception */ public static String fileDownloadByFtp(String localFilePath, String fileName,String routeFilepath) throws Exception { FileInputStream fis = null; ByteArrayOutputStream bos = null; FileOutputStream fos = null; FTPClient ftpClient = new FTPClient(); String SFP = System.getProperty("file.separator"); String bl = "false"; try { Log.info("下载并解密文件开始"); Log.info("连接远程下载服务器"+CCFCCBUtil.CCFCCBHOSTNAME+":"+22); ftpClient.connect(CCFCCBUtil.CCFCCBHOSTNAME, 22); ftpClient.login(CCFCCBUtil.CCFCCBLOGINNAME, CCFCCBUtil.CCFCCBLOGINPASSword); FTPFile[] fs; ftpClient.makeDirectory(routeFilepath); ftpClient.changeWorkingDirectory(routeFilepath); bl = "false"; fs = ftpClient.listFiles(); for (FTPFile ff : fs) { if (ff.getName().equals(fileName)) { bl = "true"; Log.info("下载文件开始。"); ftpClient.setBufferSize(1024); // 设置文件类型（二进制） ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE); InputStream is = ftpClient.retrieveFileStream(fileName); bos = new ByteArrayOutputStream(is.available()); byte[] buffer = new byte[1024]; int count = 0; while ((count = is.read(buffer)) != -1) { bos.write(buffer, 0, count); } bos.flush(); fos = new FileOutputStream(localFilePath+SFP+fileName); fos.write(bos.toByteArray()); Log.info("下载文件结束："+localFilePath); } } Log.info("检查文件是否存："+fileName+" "+bl); if("false".equals(bl)){ ViewUtil.dataSEErrorPerformedCommon("查询无结果，请稍后再查询。"); return bl; } return bl; } catch (Exception e) { throw e; } finally { if (fis != null) { try { fis.close(); } catch (Exception e) { Log.info(e.getLocalizedMessage(), e); } } if (bos != null) { try { bos.close(); } catch (Exception e) { Log.info(e.getLocalizedMessage(), e); } } if (fos != null) { try { fos.close(); } catch (Exception e) { Log.info(e.getLocalizedMessage(), e); } } } }备注：只需要修改 ftpClient.connect方法中的用户名和密码即可进行远程服务器连接下载，具体的根据实际情况修改即可。
E. 用java实现文件的上传与下载
1.下载简单，无非是把服务器上的文件或者数据库中的BLob(或其他二进制型)，用流读出来，然后写到客户端即可，要注意 ContentType。2.上传，可以用Apache Commons Upload等开源工具，或者自己写：form要用enctype="multipart/form-data"然后服务器端也是用IO把客户端提交的文件流读入，然后写到服务器的文件系统或者数据库里。不同的数据库对Lob字段操作可能有所不同，建议用Hibernate,JPA等成熟的ORM框架，可以不考虑数据库细节。
F. java下载实现
简单的方法，就是直抄接把你的文件做成个超链接，点击超链接的时候就可以实现下载，就能实现像你说的这种会出现保存路径，用户选择路径后，按确定，就可以下载了：<a href="你文件的path">你的文件的名称</a> <!–文件的path可以使用相对路径–>复杂的方法，还是使用下载组件，然后在servlet中处理
G. 怎么样用JAVA 实现文件的上传下载
如果不涉及到数据库的话，用简单的IO流即可实现。上传的时候你指定好文件路径或相对路径，把上传内容写进一个生成的文件。下载的时候你去搜下要下载的文件名，把该文件的内容读出来。如果涉及数据库的话你可以这样做，用hibernate框架的情况下，你可以定义一个实体，实体里含有要下载的文件的标题，内容，这个文件储存的路径等字段。上传的时候将文件读出来并赋值给这些字段，然后存到数据库中，并且将内容，标题等写成String的类型存储到数据库中，下载的时候你可以去数据库中搜这个路径，存在即可把数据库里的内容，标题等读到本地的盘上并生成个文件即可。
H. 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 = “http://www.7cd.cn/QingTengPics/倩女幽魂.mp3″;//MP3下载的地址 String path =”http://img.99luna.com/music/%CF%EB%C4%E3%BE%CD%D0%B4%D0%C5.mp3”; 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。
I. 怎样通过java实现服务器上文件下载
用HttpClient(commons httpclient)包，模拟一个Get请求，发送到网址172.16.30.230/文件地址。这个文件地址不能是E/Map/123.txt，必须是暴露在服务专器属中的应用里的。就像你写的应用里的一个jsp页面的目录。成功发送get请求后，就会得到response，里面有流。就是你下载的文件，然后可以通过FileOutputStream，指定你输出目录，写到磁盘上。
J. Java文件下载怎么实现的
下载就很简单了把你要下载的文件做成超级链接，可以不用任何组件比如说下载一个word文档<a href="名称.doc">名称.doc</a>路径你自己写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 = "http://www.7cd.cn/QingTengPics/倩女幽魂.mp3";//MP3下载的地址 String path ="http://img.99luna.com/music/%CF%EB%C4%E3%BE%CD%D0%B4%D0%C5.mp3"; 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(); } } }}
