在学习下载文件的时候出现问题了
main.xml
- XML code
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" ><Button android:id="@+id/downloadTxt" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/txt" /><Button android:id="@+id/downloadMp3" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/mp3" /></LinearLayout>
AndroidManifest.xml
- XML code
<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.chk.download" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="15" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:name=".DownloadActivity" 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> <!-- 获得网络权限和SD卡的读写权限 --> <uses-permission android:name="android.permission.INTERNET"/> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/></manifest>
HttpDownloader.java
- Java code
package com.chk.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.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本当中的内容 * 1.创建一个URL对象 * 2.通过URL对象,创建一个HttpURLConnection对象 * 3.得到InputStream * 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 { url = new URL(urlStr); HttpURLConnection urlConn = (HttpURLConnection)url.openConnection(); 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 (IOException e) { e.printStackTrace(); } } return sb.toString(); } /** * * @param urlStr * @param path * @param fileName * @return * -1:文件下载出错 * 0:文件下载成功 * 1: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) { e.printStackTrace(); } } return 0; } /** * 根据URL得到输入流 * @param urlStr * @return */ public InputStream getInputStreamFromURL(String urlStr) { HttpURLConnection urlConn = null; InputStream inputStream = null; try { url = new URL(urlStr); urlConn = (HttpURLConnection)url.openConnection(); inputStream = urlConn.getInputStream(); } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } return inputStream; }}
FileUtils.java
- Java code
package com.chk.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;public class FileUtils { private String SDPATH; private int FILESIZE = 4 * 1024; public String getSDPATH(){ return SDPATH; } public FileUtils(){ //得到当前外部存储设备的目录( /SDCARD ) SDPATH = Environment.getExternalStorageDirectory() + "/"; } /** * 在SD卡上创建文件 * @param fileName * @return * @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 * @return */ public File createSDDir(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 * @param fileName * @return */ 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 * @param path * @param fileName * @param input * @return */ 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[FILESIZE]; while((input.read(buffer)) != -1){ output.write(buffer); } output.flush(); } catch (Exception e) { e.printStackTrace(); } finally{ try { output.close(); } catch (IOException e) { e.printStackTrace(); } } return file; }}DownloadActivity.java
- Java code
package com.chk.download;import com.chk.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 DownloadActivity extends Activity { private Button downlaodTxtButton ; private Button downlaodMP3Button ; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); downlaodTxtButton = (Button)findViewById(R.id.downloadTxt); downlaodTxtButton.setOnClickListener(new DownloadTxtListener()); downlaodMP3Button = (Button)findViewById(R.id.downloadMp3); downlaodMP3Button.setOnClickListener(new DownloadMP3Listener()); } class DownloadTxtListener implements OnClickListener{ public void onClick(View v) { HttpDownloader downloader = new HttpDownloader(); String lrc = downloader.download("http://localhost:8080/MyTxt/test.txt"); System.out.println(lrc); } } class DownloadMP3Listener implements OnClickListener{ public void onClick(View v) { HttpDownloader downloader = new HttpDownloader(); int result = downloader.downFile("http://localhost:8080/MyTxt/1.mp3", "MP3/", "1.map3"); System.out.println(result); } }}我的Tomcat已经正常启动，Tomcat中定义的路径是<Context path="" docBase="D:\MyWeb"></Context>，所以我在D:\MyWeb目录下新建了MyTxt目录，在MyTxt目录下有两个文件：test.txt和1.mp3，当我部署后，点击下载文本文件这个按钮的时候，出现的错误提示如下：
- XML code
02-21 22:26:46.359: E/AndroidRuntime(1038): FATAL EXCEPTION: main02-21 22:26:46.359: E/AndroidRuntime(1038): java.lang.NullPointerException02-21 22:26:46.359: E/AndroidRuntime(1038): at com.chk.utils.HttpDownloader.download(HttpDownloader.java:43)02-21 22:26:46.359: E/AndroidRuntime(1038): at com.chk.download.DownloadActivity$DownloadTxtListener.onClick(DownloadActivity.java:30)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.view.View.performClick(View.java:3511)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.view.View$PerformClick.run(View.java:14105)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.os.Handler.handleCallback(Handler.java:605)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.os.Handler.dispatchMessage(Handler.java:92)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.os.Looper.loop(Looper.java:137)02-21 22:26:46.359: E/AndroidRuntime(1038): at android.app.ActivityThread.main(ActivityThread.java:4424)02-21 22:26:46.359: E/AndroidRuntime(1038): at java.lang.reflect.Method.invokeNative(Native Method)02-21 22:26:46.359: E/AndroidRuntime(1038): at java.lang.reflect.Method.invoke(Method.java:511)02-21 22:26:46.359: E/AndroidRuntime(1038): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)02-21 22:26:46.359: E/AndroidRuntime(1038): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)02-21 22:26:46.359: E/AndroidRuntime(1038): at dalvik.system.NativeStart.main(Native Method)
请各位帮帮忙！到底是哪里出了问题
我是在虚拟机上运行的，因为没有实体机
错误提示如下两行代码出错！
- Java code
buffer.close();
- Java code
String lrc = downloader.download("http://localhost:8080/MyTxt/test.txt");[解决办法]
ip改成10.0.0.2，一定可以，这会android虚拟机映射的本机电脑的ip
[解决办法]
是在HttpDownloader.java这个文件！
String lrc = downloader.download("http://localhost:8080/MyTxt/test.txt");这里也要改：把localhost改成你的IP地址！