浅入浅出Android（014）：HTTP GET获取文本内容

Androidstudio版本：0.8.6；虚拟机版本：4.*。

1、建立android项目MyApplication

2、修改布局文件activity_my.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    android:paddingBottom="@dimen/activity_vertical_margin"    tools:context=".MyActivity">    <Button        android:id="@+id/button01"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="获取网页内容" />    <ScrollView        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:layout_below="@+id/button01">        <TextView            android:id="@+id/textview01"            android:text=""            android:layout_width="wrap_content"            android:layout_height="wrap_content" />    </ScrollView></RelativeLayout>

ScrollView用于给Textview添加滚动条。

3、添加联网权限

在AndroidManifest.xml添加<uses-permission android:name="android.permission.INTERNET" />，文件最终内容是：

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.example.letian.myapplication" >    <uses-permission android:name="android.permission.INTERNET" />    <application        android:allowBackup="true"        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <activity            android:name=".MyActivity"            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></manifest>

4、修改MyActivity.java

package com.example.letian.myapplication;import android.app.Activity;import android.os.Bundle;import android.os.StrictMode;import android.view.View;import android.widget.Button;import android.widget.TextView;import org.apache.http.HttpResponse;import org.apache.http.HttpStatus;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.DefaultHttpClient;import java.io.BufferedReader;import java.io.InputStreamReader;public class MyActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_my);        final Button btn01 = (Button) this.findViewById(R.id.button01);        final TextView tv01 = (TextView) this.findViewById(R.id.textview01);        btn01.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                tv01.setText(getUrlContent("http://www.oschina.net/"));            }        });    }    private String getUrlContent(String url) {        HttpGet getRequest = new HttpGet(url);        getRequest.addHeader("User-Agent", " Mozilla/5.0 (Windows NT 6.3; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0");        try {            HttpResponse response = new DefaultHttpClient().execute(getRequest);            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {                BufferedReader in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));                StringBuffer sb = new StringBuffer("");                String line = ""; //存储读取的一行内容                String NL = System.getProperty("line.separator");  //换行符                while ((line = in.readLine()) != null) {                    sb.append(line+NL);                }                in.close();                return sb.toString();            } else {                return "读取失败：\n"+response.getStatusLine().getStatusCode();            }        } catch (Exception e) {            return "读取失败:\n"+e.toString();        }    }}

5、但是运行结果并不令人满意，出现异常

网页请求时一个阻塞的过程，如果时间过长会造成程序假死，所以产生了该异常。这个异常在较新版本的Android中才提出。

6、一个并不推荐的解决办法

该方法可能会造成程序假死，所以最好不要在app中使用该方法。

在onCreate()的适当位置添加如下内容：

if (android.os.Build.VERSION.SDK_INT > 9) {    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();    StrictMode.setThreadPolicy(policy);}

app运行结果如下：

7、使用线程的方法来解决（推荐）

将MyActivity.java修改如下：

package com.example.letian.myapplication;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Button;import android.widget.TextView;import org.apache.http.HttpResponse;import org.apache.http.HttpStatus;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.DefaultHttpClient;import java.io.BufferedReader;import java.io.InputStreamReader;public class MyActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_my);        final Button btn01 = (Button) this.findViewById(R.id.button01);        final TextView tv01 = (TextView) this.findViewById(R.id.textview01);        final Handler handler = new Handler(){            @Override            public void handleMessage(Message msg) {                super.handleMessage(msg);                Bundle data = msg.getData();                tv01.setText(data.getString("value"));            }        };        final Runnable runnable = new Runnable(){            @Override            public void run() {                String result = getUrlContent("http://www.oschina.net/");                Message msg = new Message();                Bundle data = new Bundle();                data.putString("value", result);                msg.setData(data);                handler.sendMessage(msg);            }        };        btn01.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                new Thread(runnable).start();            }        });    }    /**     * 获取url对应的网页内容     * @param url     * @return     */    private String getUrlContent(String url) {        HttpGet getRequest = new HttpGet(url);        getRequest.addHeader("User-Agent", " Mozilla/5.0 (Windows NT 6.3; WOW64; rv:32.0) Gecko/20100101 Firefox/32.0");        try {            HttpResponse response = new DefaultHttpClient().execute(getRequest);            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {                BufferedReader in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));                StringBuffer sb = new StringBuffer("");                String line = ""; //存储读取的一行内容                String NL = System.getProperty("line.separator");  //换行符                while ((line = in.readLine()) != null) {                    sb.append(line+NL);                }                in.close();                return sb.toString();            } else {                return "读取失败：\n"+response.getStatusLine().getStatusCode();            }        } catch (Exception e) {            return "读取失败:\n"+e.toString();        }    }}

参考：

http://stackoverflow.com/questions/6343166/android-os-networkonmainthreadexception
Android编程典型实例与项目开发吴亚峰等编