android:文件下载

1 . 使用 http 协议下载文件

A ) : 创建一个 HttpURLConection 对象
HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();
B ) : 获取一个 InputStream
urlConn.getInputStream();
C ) : 访问网络的权限
android.permission.INTERNET

1 . 声明控件对象 ( 略 )
2 . 获得控件对象 ( 略 )
3 . 绑定事件 ( 略 )
4 . 创建监听器对象

// 封装方法 httpDownloader

public class DownloadHelper {private URL url = null;public String download(String newUrl){StringBuffer sb = new StringBuffer();String line = null;BufferedReader br = null;//创建一个url对象；try {url = new URL(newUrl);//创建一个http连接HttpURLConnection urlConn  = (HttpURLConnection)url.openConnection();br = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));while((line = br.readLine())!=null){sb.append(line);System.out.println(sb.toString());}} catch (Exception e) {e.printStackTrace();} finally{try{br.close();}catch (Exception e) {e.printStackTrace();}}return sb.toString();}//返回-1下载文件出错，返回0下载成功，返回1文件已经存在public int downFile(String urlStr,String path,String fileName){try {InputStream is = null;FileUtils fileUtils = new FileUtils();if(fileUtils.existSDFile(path+fileName)){return 1;}else{//inputStream = 上个从网络上获得的输入流is = getInputStreamFromUrl(urlStr);File resultFile = fileUtils.write2SDCARDFromInputSteam(path, fileName, is);if(resultFile==null)return -1;}} catch (Exception e) {e.printStackTrace();}return 0;}public InputStream getInputStreamFromUrl(String newUrl){URL url = null;HttpURLConnection httpURLConnection = null;InputStream is = null;try {url = new URL(newUrl);httpURLConnection = (HttpURLConnection)url.openConnection();is = httpURLConnection.getInputStream();} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return is;}}

2 . 将下载的文件写入 SDCARD
访问 SDCARD
// 得到当前设备 sdka 的目录
Environment.getExternalStorageDirectory();
// 访问 SD 卡的权限
Android.permission.WRITE_EXTERNAL_STORAGE
例 : // 一个完整的访问封装类

public class FileUtils {private String SDCARD = null;public FileUtils() {SDCARD = Environment.getExternalStorageDirectory() + "/";}// 创建一个目录public File createSDDir(String dirName) {File fileDir = new File(SDCARD + dirName);fileDir.mkdir();return fileDir;}// 创建一个文件；public File createSDFile(String fileName) throws IOException {File file = new File(SDCARD+fileName);   //注意在这里一定要加上主目录 SDCARD中，才可以，不然会找不到目录 。file.createNewFile();return file;}// 判断SD卡上的文件是不是存在；public boolean existSDFile(String fileName) {File file = new File(SDCARD + fileName);return file.exists();}// 将一个流对象写入SDCARDpublic File write2SDCARDFromInputSteam(String path, String fileName,InputStream is) {File file = null;OutputStream os = null;try {createSDDir(path);file = createSDFile(path + fileName);os = new FileOutputStream(file);byte[] buffer = new byte[4 * 1024];while (is.read(buffer) != -1) {os.write(buffer);}os.flush();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {try {os.close();is.close();} catch (IOException e) {e.printStackTrace();}}return file;}}

最后在 AndroidManifest,xml 中加入标签
<user-permission android:name="android.permission. WRITE_EXTERNAL_STORAGE" />

DownloadActivity.java

package com.example.android.apis;import com.example.android.download.DownloadHelper;import android.app.Activity;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class DownloadActivity extends Activity {    /** Called when the activity is first created. */Button down_txt = null;Button down_mp3 = null;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        down_txt = (Button)findViewById(R.id.download_txt);        down_mp3 = (Button)findViewById(R.id.download_mp3);                down_txt.setOnClickListener(new MyDownload_txt());        down_mp3.setOnClickListener(new MyDownload_mp3());    }        class MyDownload_txt implements OnClickListener{@Overridepublic void onClick(View v) {DownloadHelper downloadHelper = new DownloadHelper();downloadHelper.download("http://192.168.137.3:8080/test.lrc");}        }        class MyDownload_mp3 implements OnClickListener{@Overridepublic void onClick(View v) {DownloadHelper downloadHelper = new DownloadHelper();downloadHelper.downFile("http://192.168.137.3:8080/test.lrc", "test/","test.mp3");}        }}

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