java读取远程文件

java读取本地文件大家都不陌生，而且实现也相对轻松。java读取远程文件怎么实现呢？

使用到的Java的核心类：java.net.URL，java.net.URLConnection，java.net.HttpURLConnection

原理：

(1)使用文件地址创建URL,如

URLurl = new URL(url)

(2)创建url连接，如：URLConnection urlconn=url.openConnection()

(3)转化url连接为httpUrl连接，如：HttpURLConnection httpconn = (HttpURLConnection) urlconn;   

(4)读取httpconn的流，如httpconn.getInputStream()或

缓存读取流：BufferedInputStream bis=new BufferedInputStream(httpconn.getInputStream()); 

(5).读到byte数组，如：while((r=bis.read(b))>0);

 

总结：最大的感受就是网络读取文件和本地读取的区别。本地文件就是file,而网络上文件是一个URL。这是我自己的理解，可能有点误解吧。

 

ps一下代码：

import java.io.BufferedInputStream;
import java.io.File;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

public class FileDownload {
	public static void main(String[] args) throws IOException {
		//String remote_img_url="http://zhbccrm.xicp.net:8008/v1/tfs/T1WaJTByxT1R4cSCrK.png";
		String remote_img_url="http://img.baidu.com/img/iknow/sula201506/baiduzhidaowenkugaokao.png?t=1433819530";
		URL url=null;
		URLConnection urlconn=null;
		HttpURLConnection httpconn=null;
		BufferedInputStream bis=null;
		try {
			url = new URL(remote_img_url);
			urlconn = url.openConnection();
			//1.5以后URLConnection设置连接超时，从主机读取数据超时 单位：毫秒
			/*urlconn.setConnectTimeout(10000);
			urlconn.setReadTimeout(20000);*/
			httpconn = (HttpURLConnection) urlconn;   
			int httpResult = httpconn.getResponseCode();  
			System.out.println("httpResult::"+httpResult);
			if(httpResult==HttpURLConnection.HTTP_OK){
				int filesize = urlconn.getContentLength(); // 取数据长度
				byte[] b=new byte[filesize];
				bis=new BufferedInputStream(httpconn.getInputStream());   
				int r=0;
				while((r=bis.read(b))>0);
				System.out.println("length::"+filesize);
				//System.out.println("string:"+new String(b,"UTF-8"));
			}
		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}finally{
			if(httpconn!=null)
				httpconn.disconnect();
			if(bis!=null){
				bis.close();
			}
		}
	}
}

 

 总结：使用httpClient实现远程访问服务，怎么判断