handler以及AnyscTask处理机制

1、Handler

主文件：MainActivity.java

package com.example.asynctaskdownload;

import java.io.IOException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
 protected static final int SHOW_RESPONSE = 0;
/** Called when the activity is first created. */
    private TextView textView;
    private String result = "";

/////////////////////////////////////////////////////////
    private Handler handler = new Handler(){

        public void handleMessage(Message msg)
        {
            switch(msg.what){
            case SHOW_RESPONSE:
                String result = (String)msg.obj;
                //注意是在此处进行UI操作
                textView.setText(result);
            }
        }
    };
/////////////////////////////////////////////////////
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView) findViewById(R.id.TextView01);
    Button button = (Button) findViewById(R.id.readWebpage);
    button.setOnClickListener(new OnClickListener()
    {

        @Override
        public void onClick(View v) {
            //
            //textView.setText(result);
            if(v.getId() == R.id.readWebpage)
            {
                sendRequestHttpUrl();
            }
        }

    });
}
////////////////////////////////////////////////////////
protected void sendRequestHttpUrl() {
    // TODO Auto-generated method stub
    //
    new Thread(new Runnable()
    {

        @Override
        public void run() {
            // 

            try
            {
                HttpClient client = new DefaultHttpClient();
                HttpGet httpGet = new HttpGet("http://10.0.2.2:8080/mp3/a1.lrc");

                HttpResponse response = client.execute(httpGet);
                StatusLine statusLine = response.getStatusLine();
                int statusCode = statusLine.getStatusCode();
                if (statusCode == 200) {
                    HttpEntity entity = response.getEntity();
                    //关于此处中文乱码问题解决？文本文件保存时，文本文档默认为ANSI编码格式，另存为时手动改为utf-8格式即可
                    result = EntityUtils.toString(entity, "utf-8");
                }
                Message message = new Message();
                message.what = SHOW_RESPONSE;
                message.obj = result.toString();
                handler.sendMessage(message);
            }catch(Exception ex)
            {
                ex.printStackTrace();
            }

        }

    }
    ).start();
}
}

activity_main.xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/readWebpage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Load Webpage" >
    </Button>
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <TextView
        android:id="@+id/TextView01"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Placeholder" >
        </TextView>
    </ScrollView>

</LinearLayout> 

运行结果：

2、AnyscTask

主代码：

package com.example.asynctaskdownload;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
  private TextView textView;

  private final String fileName = "a1.lrc";
  //private final String fileUrl = "http://10.0.2.2:8080/mp3/a1.lrc";
  private int result = Activity.RESULT_CANCELED;
  private String response = "";

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView) findViewById(R.id.TextView01);
    Button button = (Button) findViewById(R.id.readWebpage);
    button.setOnClickListener(new OnClickListener()
    {

        @Override
        public void onClick(View v) {
            // 

            DownloadWebPageTask task = new DownloadWebPageTask();
            //task.execute(new String[] { "http://www.vogella.com" });
            task.execute(new String[] { "http://10.0.2.2:8080/mp3/a1.lrc" });
            Toast.makeText(MainActivity.this, "Download Success!", Toast.LENGTH_LONG).show();

//            textView.setText(response);
        }

    });
  }

  private class DownloadWebPageTask extends AsyncTask<String, Void, Integer> {
    @Override
    protected Integer doInBackground(String... urls) {
      //获取sdcard的路径，以及设置保存的文件名
      File output = new File(Environment.getExternalStorageDirectory(), fileName);
      if(output.exists())
      {
          output.delete();//若同名文件已存在则删除
      }

//      String response = "";
      InputStream content = null;
      FileOutputStream fos = null;
      //遍历url数组中的url，采用HttpClient(接口)的方式访问网络
      for (String url : urls) {
        //首先创建一个DefaultHttpClient实例
        DefaultHttpClient client = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);//发起一个GET请求，创建一个HttpGet对象，并传入目标网络地址
        try {
          HttpResponse execute = client.execute(httpGet);//调用execute执行访问请求并返回一个HttpResponse对象
          if(execute.getStatusLine().getStatusCode() == 200)
          {
              //注:下面两行code只能使用其中一个：content will be consume only once
              //execute.getEntity()调用了两次
 //             content = execute.getEntity().getContent();//获取服务返回的具体内容
              //调用EntityUtils.toString该静态方法将HttpEntity转换成字符串,为避免中文字符乱码，添加utf-8字符集参数
//              response = EntityUtils.toString(execute.getEntity(), "utf-8");
//////////////////////////////////////////////////////////////////////////////
              HttpEntity entity = execute.getEntity();
 //             response = EntityUtils.toString(entity, "utf-8");
              content = entity.getContent();

          }

          //利用管道 inputstream-->reader
          InputStreamReader reader = new InputStreamReader(content);
          fos = new FileOutputStream(output.getPath());

          int next = -1;
          while ((next = reader.read()) != -1) {
            fos.write(next);
          }

          result = Activity.RESULT_OK;

//          BufferedReader buffer = new BufferedReader(new InputStreamReader(content));

//          String s = "";
//          while ((s = buffer.readLine()) != null) {
//            response += s;
//          }

        } catch (Exception e) {
          e.printStackTrace();
        }finally {
            if (content != null) {
                try {
                  content.close();
                } catch (IOException e) {
                  e.printStackTrace();
                }
              }
              if (fos != null) {
                try {
                  fos.close();
                } catch (IOException e) {
                  e.printStackTrace();
                }
              }
      }
    }
    return result;
  }

    protected void onPostExecute(Integer result) {
    //此处可以根据后台任务完成后返回的结果进行一些UI操作

        if(result == Activity.RESULT_OK)
        {
            textView.setText("mp3 file download success!!");
        }
    }

 /* public void onClick(View view) {
    DownloadWebPageTask task = new DownloadWebPageTask();
    //task.execute(new String[] { "http://www.vogella.com" });
    task.execute(new String[] { "http://10.0.2.2:8080/mp3/a1.lrc" });

  }*/

  }
}

activity_main.xml文件同上

运行结果：成功下载文件a1.lrc到sdcard中