关于下载文件封装的两个类(Mars)

首先是文件FileUtils.java

package mars.utils;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

import mars.model.Mp3Info;
import android.os.Environment;

public class FileUtils {
	private String SDCardRoot;

	public FileUtils() {
		// 得到当前外部存储设备的目录
		SDCardRoot = Environment.getExternalStorageDirectory()
				.getAbsolutePath()
				+ File.separator;
	}

	/**
	 * 在SD卡上创建文件
	 * 
	 * @throws IOException
	 */
	public File createFileInSDCard(String fileName, String dir)
			throws IOException {
		File file = new File(SDCardRoot + dir + File.separator + fileName);
		System.out.println("file---->" + file);
		file.createNewFile();
		return file;
	}

	/**
	 * 在SD卡上创建目录
	 * 
	 * @param dirName
	 */
	public File creatSDDir(String dir) {
		File dirFile = new File(SDCardRoot + dir + File.separator);
		System.out.println(dirFile.mkdirs());
		return dirFile;
	}

	/**
	 * 判断SD卡上的文件夹是否存在
	 */
	public boolean isFileExist(String fileName, String path) {
		File file = new File(SDCardRoot + path + File.separator + 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 {
			creatSDDir(path);
			file = createFileInSDCard(fileName, path);
			output = new FileOutputStream(file);
			byte buffer[] = new byte[4 * 1024];
			int temp;
			while ((temp = input.read(buffer)) != -1) {
				output.write(buffer, 0, temp);
			}
			output.flush();
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				output.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return file;
	}

}

然后是下载的HttpDownload.java

package mars.download;

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;

import mars.utils.FileUtils;


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(fileName,path)) {
				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;
	}
}

注意使用的时候需要添加相应的权限，还有需要开辟新的线程，以为安卓不能在主线程中执行耗时的操作(比如：下载文件)

下面是我自己写的一个，没什么技术含量，纯给新手测试用用：

package com.example.httpdownload;

import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

public class MainActivity extends Activity {
	Button downButton;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		downButton = (Button) findViewById(R.id.button1);
		if (savedInstanceState == null) {
			getFragmentManager().beginTransaction()
					.add(R.id.container, new PlaceholderFragment()).commit();
		}
		downButton.setOnClickListener(listener);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}

	/**
	 * A placeholder fragment containing a simple view.
	 */
	public static class PlaceholderFragment extends Fragment {

		public PlaceholderFragment() {
		}

		@Override
		public View onCreateView(LayoutInflater inflater, ViewGroup container,
				Bundle savedInstanceState) {
			View rootView = inflater.inflate(R.layout.fragment_main, container,
					false);
			return rootView;
		}
	}

	View.OnClickListener listener = new View.OnClickListener() {

		public void onClick(View v) {
			// TODO Auto-generated method stub
			switch (v.getId()) {
			case R.id.button1:
				Thread thread = new Thread(new MyRunable());
				thread.start();
				break;

			default:
				break;
			}
		}
	};

	private void downLoadFile() {
		String urlStr = "http://10.3.19.26:8080/2015-1-6/1.txt";
		HttpDownloader httpDownloader = new HttpDownloader();
		int result = httpDownloader.downFile(urlStr, "", " 1.txt");
		System.out.println("<-------->" + result);
	}

	public class MyRunable implements Runnable {

		public void run() {
			// TODO Auto-generated method stub
			downLoadFile();
		}

	}
}