Android开发 文件下载

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声明:此代码来源于mars老师的视频教程，粘贴到这里，纯用于个人学习，方便查阅，无其它意图。

1. 使用http协议下载文件

    * 创建一个HttpURLConnection对象

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

    * 获得一个InputStream对象        - urlConn.getInputStream()

    * 访问网络的权限        - android.permission.INTENET

2.将下载文件写入sdcard

*访问sd卡的步骤：

-得到当前设备SD卡的目录：Environment.getExternalStorageDirectory()

        - 访问SD卡的权限：android.permission.WRITE_EXTERNAL_STORAGE

3. 实例代码

    Download-->Activity

package mars.download;

import mars.utils.HttpDownloader;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class Download extends Activity {
	private Button downloadTxtButton;
	private Button downloadMp3Button;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		downloadTxtButton = (Button) findViewById(R.id.downloadTxt);
		downloadTxtButton.setOnClickListener(new DownloadTxtListener());

		downloadMp3Button = (Button) findViewById(R.id.downloadMp3);
		downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
	}

	class DownloadTxtListener implements OnClickListener {

		@Override
		public void onClick(View v) {
			HttpDownloader httpDownloader = new HttpDownloader();
			String lrc = httpDownloader
					.download("http://9.125.233.**:8080/mp3/a1.lrc");
			System.out.println(lrc);
		}

	}

	class DownloadMp3Listener implements OnClickListener {

		@Override
		public void onClick(View v) {
			HttpDownloader httpDownloader = new HttpDownloader();
			int result = httpDownloader.downFile(
					"http://9.125.233.**:8080/mp3/a1.mp3", "voa/", "a1.mp3");
			System.out.println(result);
		}

	}
}

    HttpDownloader

package mars.utils;

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.URL;

public class HttpDownloader {

	private URL url = null;

	/**
	 * 根据URL下载文件，前提是这个文件中的内容是文本，函数的返回值就是文件的内容
	 * 1.创建一个URL对象
	 * 2.通过URL对象，创建一个HttpURLConnection对象
	 * 3.得到InputStream
	 * 4.从InputStream中读取数据
	 */
	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();
			buffer = new BufferedReader(new InputStreamReader(urlConn
					.getInputStream()));
			// 使用IO流读取数据
			while ((line = buffer.readLine()) != null) {
				sb.append(line);
			}

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				buffer.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		return sb.toString();
	}

	/**
	 * 将下载的mp3文件写到sdcard
	 * 
	 * 该函数放回整型-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 (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		return 0;
	}

	private InputStream getInputStreamFromUrl(String urlStr) throws IOException {
		url = new URL(urlStr);
		HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
		InputStream inputStream = urlConn.getInputStream();
		return inputStream;
	}

}

    工具类FileUtils

package mars.utils;

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

import android.os.Environment;
/**
 * 访问sdcard的工具函数
 * */
public class FileUtils {

	private String SDPATH;

	public String getSDPATH() {
		return SDPATH;
	}
	public void setSDPATH(String sdpath) {
		SDPATH = sdpath;
	}
	public FileUtils() {
		// 得到当前外部存储设备的目录,即: /SDCARD
		SDPATH = Environment.getExternalStorageDirectory() + "/";
	}
	/**
	 * 在SD卡上创建文件
	 * 
	 */
	public File creatSDFile(String fileName) throws IOException {
		File file = new File(SDPATH + fileName);
		file.createNewFile();
		return file;
	}

	/**
	 * 在SD卡上创建目录
	 */
	public File createDir(String dirName) {
		File dir = new File(SDPATH + dirName);
		dir.mkdir();
		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 {
			createDir(path);//创建目录
			File f = creatSDFile(path + fileName);//创建文件
			output = new FileOutputStream(f);
			byte buffer[] = new byte[4 * 1024];
			while ((input.read(buffer)) != -1) {
				output.write(buffer);
			}
			System.out.println(path);
			file = new File(path);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				output.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return file;
	}
}

    AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="mars.download"
      android:versionCode="1"
      android:versionName="1.0">
    <uses-sdk android:minSdkVersion="4" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".Download"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
    <!--必须添加以下权限，才能实现下载操作-->
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</manifest>