使用HTTP协议下载文件

为了测试方便，在自己的电脑上开一个web服务Tomcat，在Tomcat的webapps文件夹里放测试下载用的文件

在cmd的ipconfig指令下查看自己的主机的IP地址。

之前没有接触过Tomcat，就先按网上介绍的安装教程下载Tomcat，并在Eclipse配置好Tomcat

http://blog.chinaunix.net/uid-25434387-id-167705.html

初次安装配置会出现一些错误，但在网上都能找到解决办法，直到Tomcat正常工作

使用HTTP·协议下载文件：

1、创建一个HttpURLConnection对象

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

2、获得一个InputStream对象

InputStream inputStream = urlConn.getInputStream();

3、访问网络的权限（需要在AndroidMainfest.xml配置好）

<uses-permission android:name="android.permission.INTERNET"/>

将下载的文件写到SDCard

1、得到当前设备SD卡的目录

SDPATH = Environment.getExternalStorageDirectory() + "/";

2、访问SD的权限（同样需要在AndroidMainfest.xml配置好）

 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

例程：

Download.java

import mars.utils.HttpDownloader;
import android.annotation.SuppressLint;
import android.annotation.TargetApi;
import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.os.StrictMode;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Download extends Activity {

	private Button downloadTxtButton;
	private Button downloadMp3Button;
	@TargetApi(Build.VERSION_CODES.GINGERBREAD)
	@SuppressLint("NewApi")
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		
		downloadTxtButton = (Button)findViewById(R.id.downloadText);
		downloadMp3Button = (Button)findViewById(R.id.downloadMp3);
		downloadTxtButton.setOnClickListener(new OnClickListener(){
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				HttpDownloader httpDownloader = new HttpDownloader();
				String lrc = httpDownloader.download("http://222.199.230.116:8080/mp3/Test-2.lrc");				
				System.out.println(lrc);
			}
		});
		downloadMp3Button.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				HttpDownloader httpDownloader = new HttpDownloader();
				int result = httpDownloader.downFile("http://222.199.230.116:8080/mp3/Test-2.mp3","voa/","Test.mp3");
				System.out.println(result);				
			}
		});
		
		StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().
				detectDiskWrites().detectNetwork().penaltyLog().build());
		
	}


}

在Android4.0以上的模拟器好像对联网下载文件好像有要求，所以在.java文件要配置：

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().detectDiskReads().
				detectDiskWrites().detectNetwork().penaltyLog().build());

详情请看http://www.cnblogs.com/Lewis/p/3298994.html

FileUtils.java

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.os.Environment;

public class FileUtils {
	private String SDPATH;
	public String getSDPATH(){
		return SDPATH;
	}
	public FileUtils(){
		//得到当前外部存储设备的目录
		SDPATH = Environment.getExternalStorageDirectory() + "/";
	}
	/**
	 * 在SD卡上创建文件
	 * 
	 * @throws IOException
	 */
	public File createSDFile(String fileName) throws IOException{
		File file = new File(SDPATH + fileName);
		file.createNewFile();
		return file;	
	}
	/**
	 * 在SD卡上创建目录
	 * 
	 * @param dirName
	 */
	public File createSDDir(String dirName){
		File dir = new File(SDPATH + dirName);
		dir.mkdirs();
		return dir;
	}
	/**
	 * 判断SD卡上的文件夹是否存在
	 */
	public boolean isFileExist(String fileName){
		File file = new File(SDPATH + fileName);
		return file.exists();
	}
	/**
	 * 将一个InputStream里面的数据写入到SD卡中
	 */
	public File write2SDFromInput(String path,String fileName,InputStream input){
		File file = null;
		OutputStream output = null;
		try{
			createSDDir(path);
			file = createSDFile(path + fileName);
			output = new FileOutputStream(file);
			byte buffer [] = new byte[4 * 1024];
			while((input.read(buffer)) != -1){
				output.write(buffer);
			}
			output.flush();
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			try{
				output.close();
			}catch(Exception e){
				e.printStackTrace();
			}
			
		}
		return file;
	}
}

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class HttpDownloader {
	
	private URL url = null;
	/**
	 * 根据URL下载文件，前提是这个文件当中的内容是文本，函数的返回值就是文件当中的内容
	 * 1.创建一个URL对象
	 * 2.通过URL对象，创建一个HttpURLConnection对象
	 * 3.得到InputStram
	 * 4.从InputStream当中读取数据
	 * @param urlStr
	 * @return
	 */
	public String download(String urlStr){
		StringBuffer sb = new StringBuffer();
		String line = null;
		BufferedReader buffer = null;
		try{
			// 创建一个URL对象
			url = new URL(urlStr);
			// 创建一个Http连接
			HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
			// 使用IO流读取数据
			buffer = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
			while((line = buffer.readLine()) != null){
				sb.append(line);
			}
			
		}catch(Exception e){
			e.printStackTrace();
			
		}finally{
			try{
				buffer.close();
				
			}catch(Exception e){
				e.printStackTrace();
			}
		}
		return sb.toString();
	}
	
	/**
	 * 该函数返回整形 -1：代表下载文件出错    0：代表下载文件成功     1：代表文件已经存在
	 */
	public int downFile(String urlStr, String path, String fileName){
		InputStream inputStream = null;
		try{
			FileUtils fileUtils = new FileUtils();
			if(fileUtils.isFileExist(path + fileName)){
				return 1;
			}else{
				inputStream = getInputStreamFromUrl(urlStr);
				File resultFile = fileUtils.write2SDFromInput(path, fileName, inputStream);
				if(resultFile == null){
					return -1;
				}
			}
			
		}catch(Exception e){
			e.printStackTrace();
			return -1;
		}finally{
			try{
				inputStream.close();
			}catch(Exception e){
				e.printStackTrace();
			}
		}
		
		return 0;
	}
	/**
	 * 根据URL得到输入流
	 * 
	 * @param urlStr
	 * @return
	 * @throws MalformedURLException
	 * @throws IOException
	 */
	public InputStream getInputStreamFromUrl(String urlStr) 
		throws MalformedURLException, IOException{
		url = new URL(urlStr);
		HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
		InputStream inputStream = urlConn.getInputStream();
		return inputStream;
	}
}

结果示意图

刚开始下载不成功，一直输出-1，

后来百度、修改，终于输出0，下载成功，把程序调通~