Question

Java文件下载怎么实现的

jsp:
<s:form action="uploadaction" enctype="multipart/form-data">
<s:file name="upload" label="选择文件"></s:file>
<s:submit value="上传" />
</s:form>

struts:
<action name="uploadaction" class="down.uploadaction">
<result name="success">/filelist.jsp</result>
<param name="savePath">/upload</param>
</action>

action:

private File upload;
private String uploadContentType;//文件类型
private String uploadFileName;//文件名字
private String savePath;//保存地址
省去了get 和set方法了
public String execute() throws Exception {
byte[] buffer = new byte[1024];

// 文件的输入流
FileInputStream fis = new FileInputStream(getUpload());
// 文件的输出流
FileOutputStream fos = new FileOutputStream(getSavePath() + "/"
+ getUploadFileName());
int length = fis.read(buffer);
System.out.println(length);
// 循环读取文件
while (length > 0) {
// 每次写入length长度的内容
fos.write(buffer, 0, length);
length = fis.read(buffer);
}
System.out.println(savePath);
fis.close();
fos.flush();
fos.close();
}

//文件类型
private String uploadFileName;//文件名字
private String savePath;//保存地址
请问这三个变量是怎么获取这些信息的他们怎么获得文件的名字 和地址定义变量名是随便定义的吗？
我说错了。。那个标题是Java上传是怎么实现的 就是我贴的那段代码，那三个变量是怎么自动实现获取文件路径和文件名字的？

Answer 1

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();
}

}

}
}