【Android学习】利用HTTP协议下载

主要内容：

---使用HTTP协议下载文件

---将下载的文件写入SDCARD

文件下载步骤：

1.创建一个HttpURLConnection对象 

HttpURLConnection urlCnn=(HttpURLConnection)url.openConnection()

2.获得一个InputStream对象

urlConn.getInputStream()

3.访问网络的权限

android.permission.INTERNET

具体实现如下：

HttpDoemload.java：

package com.down;import java.io.BufferedReader;import java.io.File;import java.io.InputStream;import java.io.InputStreamReader;import java.net.HttpURLConnection;import java.net.URL;public class HttpDownload {private URL url=null;public String dowmload(String urlString){StringBuffer sBuffer=new StringBuffer();String lineString=null;BufferedReader bufferedReader=null;try {url=new URL(urlString); HttpURLConnection httpURLConnection=(HttpURLConnection)url.openConnection();bufferedReader=new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));while ((lineString=bufferedReader.readLine())!=null) {sBuffer.append(lineString);}} catch (Exception e) {e.printStackTrace();}finally {try {bufferedReader.close();} catch (Exception e) {e.printStackTrace();}}return sBuffer.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 urlString,String path,String fileName){InputStream inputStream=null;try {FileUtil fileUtil=new FileUtil();if(fileUtil.isFileExist(path+fileName)){return 1;}else{url=new URL(urlString);HttpURLConnection httpURLConnection=(HttpURLConnection)url.openConnection();inputStream=httpURLConnection.getInputStream();File result=fileUtil.write2SDFromInput(path, fileName, inputStream);if(result==null){return -1;}}} catch (Exception e) {e.printStackTrace();return -1;}finally{try {inputStream.close();} catch (Exception e) {e.printStackTrace();}}return 0;}}

FileUtil.java：

package com.down;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 FileUtil {private String SDPATH;public String getSDPATH() {return SDPATH;}public FileUtil() {//得到当前外部存储设备的目录// /SDCARDSDPATH = Environment.getExternalStorageDirectory() + "/";}/** * 在SD卡上创建文件 *  * @throws IOException */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 *  * @param dirName */public File creatSDDir(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{creatSDDir(path);file = creatSDFile(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;}}

MainActivity.java：

package com.ye_yun_lin.httpdownload;import java.net.HttpURLConnection;import com.down.HttpDownload;import android.os.Bundle;import android.app.Activity;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class MainActivity extends Activity {private Button downlrcButton;private Button downmp3Button;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);downlrcButton=(Button)findViewById(R.id.button1);downmp3Button=(Button)findViewById(R.id.button2);downlrcButton.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {HttpDownload httpDownload=new HttpDownload();String lrc=httpDownload.dowmload("http://27.17.29.147:8080/mp3/a1.lrc");System.out.println(lrc);}});downmp3Button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {HttpDownload httpDownload=new HttpDownload();int result=httpDownload.downFile("http://27.17.29.147:8080/mp3/a1.mp3", "mp3", "a1.mp3");System.out.println(result);}});}}

在ActivityManifest中配置：

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