Android学习笔记（十一）-从Internet获取数据

URL（Uniform Resource Locator）对象代表统一资源定位器，它是指向互联网“资源”的指针。URL可以由协议名、主机、端口和资源组成。通过url.openConnection()可以获取一个HttpURLConnection对象，通过这个对象的getInputStream()方法就可以获取网络上的数据了，如图片、网页内容等,这跟在J2SE中是一样的。

Android应用要想访问网络上的数据，还需要在AndroidManifest.xml文件中添加访问权限：

<!-- 访问internet权限 -->
<uses-permission android:name="android.permission.INTERNET"/>

下面介绍一个通过URL访问图片和Html的实例：

布局文件layout/main.xml

<?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" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/urlpath" /> <EditText android:id="@+id/urlpath" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="http://www.baidu.com/img/baidu_sylogo1.gif" /> <Button android:id="@+id/imagebutton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/imagebutton" /> <Button android:id="@+id/htmlbutton" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/htmlbutton" /> <ImageView android:id="@+id/showimage" android:layout_width="fill_parent" android:layout_height="300dip" android:scaleType="fitCenter" /> <ScrollView android:layout_width="fill_parent" android:layout_height="fill_parent"> <EditText android:id="@+id/showhtml" android:minLines="5" android:layout_width="fill_parent" android:layout_height="wrap_content" /> </ScrollView> </LinearLayout> 数据文件：values/strings.xml

<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, URLActivity!</string> <string name="app_name">URL测试</string> <string name="urlpath">请输入图片网络地址</string> <string name="imagebutton">显示图片</string> <string name="htmlbutton">显示文本</string> <string name="error">获取图片失败</string> </resources>
Activity,URLActivity.java

package com.geniusxiaoyu.url; import android.app.Activity; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.ImageView; import android.widget.Toast; import com.geniusxiaoyu.service.URLService; public class URLActivity extends Activity { private static final String TAG = "URLActivity"; private EditText pathText; private EditText htmlText; private ImageView imageView; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); pathText = (EditText)findViewById(R.id.urlpath); htmlText = (EditText)findViewById(R.id.showhtml); imageView = (ImageView)findViewById(R.id.showimage); Button imagebutton = (Button)findViewById(R.id.imagebutton); //添加点击事件 imagebutton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String path = pathText.getText().toString(); //显示与隐藏组件 htmlText.setVisibility(View.GONE); imageView.setVisibility(View.VISIBLE); try { byte[] data = URLService.getBitData(path); Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);//生成位图 imageView.setImageBitmap(bitmap);//显示图片 } catch (Exception e) { Toast.makeText(URLActivity.this, R.string.error, 1).show(); Log.e(TAG, e.toString()); } } }); Button htmlbutton = (Button)findViewById(R.id.htmlbutton); //添加点击事件 htmlbutton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String path = pathText.getText().toString(); //显示与隐藏组件 imageView.setVisibility(View.GONE); htmlText.setVisibility(View.VISIBLE); try { byte[] data = URLService.getBitData(path); String html = new String(data); //显示文本 htmlText.setText(html); } catch (Exception e) { Toast.makeText(URLActivity.this, R.string.error, 1).show(); Log.e(TAG, e.toString()); } } }); } }
URLService.java

package com.geniusxiaoyu.service; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.URL; import com.geniusxiaoyu.utils.StreamTool; public class URLService { /** * 获取图片数据 * @param path * @return * @throws Exception */ public static byte[] getBitData(String path) throws Exception{ URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection)url.openConnection(); conn.setConnectTimeout(1000 * 5); conn.setRequestMethod("GET"); InputStream is = conn.getInputStream(); return StreamTool.readInputStream(is); } }
StreamTool.java

package com.geniusxiaoyu.utils; import java.io.ByteArrayOutputStream; import java.io.InputStream; public class StreamTool { /** * 从输入流中获取数据 * @param is * @return */ public static byte[] readInputStream(InputStream is) throws Exception{ ByteArrayOutputStream baos = new ByteArrayOutputStream(); byte[] buf = new byte[1024]; int len = 0; while((len = is.read(buf)) != -1){ baos.write(buf, 0, len); } baos.close(); return baos.toByteArray(); } }
AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.geniusxiaoyu.url" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".URLActivity" 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> <uses-sdk android:minSdkVersion="8" /> <!-- 访问internet权限 --> <uses-permission android:name="android.permission.INTERNET"/> </manifest>