将访问服务器的工作交由Service承担

前面的两篇文章里面讲了移动客户端和服务器端的数据交互与显示

但是我们知道Activity是主要负责界面的，那么在activity中不应该承担太多的访问服务器的任务。也就是说，上一篇的文章所讲述的内容，虽然可行。但对于系统的架构来说，还是将责任明确划分。Activity负责界面的显示，而Service负责访问服务器。

本文将展示android端（Activity和Service）的代码，服务器端（servlet）的代码。其数据传递的过程如下：

这一切的大前提是Activity与Service绑定。如果绑定好了以后，数据的传输过程：

1. Activity将数据通过intent传递给Service。这个数据一般是一个查询条件，如（id）

2. Service提取相应的数据值，封装到json中发送request给服务器Servlet

3. Servlet通过查询条件查询结果，并将结果返回给Service

4. Service得到response后提取数据，得到的数据通过一个本地方法（call）或回调方法（callback）将结果传递给Activity

5. Activity通过调用调用Service的方法更新UI

以上就是上图所示的数据传输过程。

代码分为3段，Activity段负责【intent】和【callback】，Service段负责【Json+request+response】，Servlet段负责【query】

/****** Activity.java ******/
package com.example.helloworld;

import com.example.service.MsgService;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;

public class ServeActivity extends Activity {
    private MsgService msgService;
    private TextView textView;
    

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_main);
        
        textView = (TextView)findViewById(R.id.frag_text);
                
        //绑定Service
        Intent intent = new Intent(ServeActivity.this, MsgService.class);
        bindService(intent, conn, Context.BIND_AUTO_CREATE);
                
    }
    

    ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceDisconnected(ComponentName name) {
            
        }
        
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            //返回一个MsgService对象
            msgService = ((MsgService.MsgBinder)service).getService();
            //向Service通过intent传递数据
            Intent intent = new Intent();
            intent.putExtra("book_name", 1);
            //启动Service
            msgService.onStart(intent, 0);//设置回调函数。那么在Service中，直接调用onProgress方法就可以直接执行本段代码
            msgService.setOnProgressListener(new OnProgressListener() {
                
                @Override
                public void onProgress(String progress) {
                    // TODO Auto-generated method stub
                    //修改UI
                    textView.setText(progress);
                }
            });
        }
    };

    @Override
    protected void onDestroy() {
        unbindService(conn);
        super.onDestroy();
    }
}

这个地方唯一需要注意的就是两段标红的函数。Activity中定义了一个回调函数onProgress，在下面的Service中，只要OnProgressListener的对象调用onProgress这个函数，就相当于是修改了Activity中的UI。这种方法很好用。不过需要先创建一个interface：

package com.example.helloworld;


public interface OnProgressListener {
    void onProgress(String progress);
}

 回调函数和本篇的大部分实现方法，来自博客 Android Service与Activity之间通信的几种方式  和 一个经典例子让你彻彻底底理解java回调机制

/******  Service.java   ********/
package com.example.service;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicHeader;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.protocol.HTTP;
import org.json.JSONObject;

import com.example.helloworld.OnProgressListener;

import android.annotation.SuppressLint;
import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;

public class MsgService extends Service {

    private int index = 2;
    private String result;
    private Handler mMainHandler, mChildHandler;
    int id;
    private OnProgressListener onProgressListener;
    
    public void onStart(Intent intent, int startId){
        System.out.println("================="+intent.getIntExtra("book_name", -1));
        //获取Activity传过来的数据
        id = intent.getIntExtra("book_name", -1);
        
        //初始化mMainHandler
        mMainHandler = new Handler(){
            public void handleMessage(Message msg){
                //detail1.setBookText((String)msg.obj);
                result = (String)msg.obj;
                if(onProgressListener != null){
                    System.out.println("==========callback function: set the textView text");
                    //调用Activity中的onProgress方法，修改UI
                    onProgressListener.onProgress((String)msg.obj);
                }
                
                System.out.println("==========main thread get the message:"+msg.obj);
                System.out.println("Finally, the message is :"+msg.obj);
                
            }
        };
        
        QueryThread thread = new QueryThread();
        thread.start();
        
        while(mChildHandler == null){
            
        }
        if(mChildHandler != null){
            //将mChildHandler加入到消息队列中
            Message childMsg = mChildHandler.obtainMessage();
            childMsg.obj = mMainHandler.getLooper().getThread().getName();
            System.out.println("==========send message to mChild: "+childMsg.obj);
            mChildHandler.sendMessage(childMsg);
        }
    }
    
    //设置回调函数的接口。Activity通过这个方法获取对象
    public void setOnProgressListener(OnProgressListener onProgressListener){
        this.onProgressListener = onProgressListener;
    }
    
    
    public void onDestroy(){
        super.onDestroy();
        mChildHandler.getLooper().quit();
    }
    public String getBookDetails(int id){
        
        StringBuilder result = new StringBuilder();
        String urlStr = "http://192.168.1.21:8080/servletTest/test";
        HttpPost post = new HttpPost(urlStr);
        
        try{

            JSONObject json = new JSONObject();
            json.put("book_id", id);
            System.out.println("=============="+json.toString());
            
            StringEntity se = new StringEntity(json.toString());
            se.setContentEncoding((Header) new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));
            post.setEntity(se);
            
            HttpClient httpClient = getHttpClient();
            HttpResponse httpResponse = httpClient.execute(post);

            int httpCode = httpResponse.getStatusLine().getStatusCode();
            if(httpCode==HttpURLConnection.HTTP_OK && httpResponse != null){
                HttpEntity entity = httpResponse.getEntity();
                InputStream inputStream = entity.getContent();
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                BufferedReader reader = new BufferedReader(inputStreamReader);
                String s;
                while((s=reader.readLine()) != null){
                    result.append(s);
                }
                reader.close();
                
                JSONObject object =  new JSONObject(result.toString());
                String str = object.getString("book_list");
                //detail1.setBookText(str);

                return str;
            }
            
        }catch(Exception exception){
            exception.printStackTrace();
        }
        return null;
    }
    
    public HttpClient getHttpClient(){
    BasicHttpParams httpParams = new BasicHttpParams();
    HttpConnectionParams.setConnectionTimeout(httpParams, 5*1000);
    HttpConnectionParams.setSoTimeout(httpParams, 10*1000);
    HttpClient client = new DefaultHttpClient(httpParams);
    return client;
}

    class QueryThread extends Thread{
        public void run(){

            //初始化消息循环队列，需要在Handler创建之前
            Looper.prepare();
            mChildHandler = new Handler(){
                public void handleMessage(Message msg){
                    //访问网络等耗时工作
                    String book_titleString = getBookDetails(id);
                    System.out.println("================book_title from servlet is "+book_titleString);
                    Message toMain = mMainHandler.obtainMessage();
                    toMain.obj = book_titleString;
                    //向主线程当前线程的Looper对发送message
                    System.out.println("================send message to main thread: "+book_titleString);
                    mMainHandler.sendMessage(toMain);
                }
            };
            //启动子线程消息循环队列
            Looper.loop();
            System.out.println("================json is done!");
        }
    }
    
    public class MsgBinder extends Binder{
        public MsgService getService(){
            
            return MsgService.this;
        }
    }
        
    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        return new MsgBinder();
    }
}

/******* Servlet.java ********/

package com.example.service;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicHeader;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.protocol.HTTP;
import org.json.JSONObject;

import com.example.helloworld.OnProgressListener;

import android.annotation.SuppressLint;
import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.Handler;
import android.os.IBinder;
import android.os.Looper;
import android.os.Message;

public class MsgService extends Service {

    private int index = 2;
    private String result;
    private Handler mMainHandler, mChildHandler;
    int id;
    private OnProgressListener onProgressListener;
    
    public void onStart(Intent intent, int startId){
        System.out.println("================="+intent.getIntExtra("book_name", -1));
        //获取Activity传过来的数据
        id = intent.getIntExtra("book_name", -1);
        
        //初始化mMainHandler
        mMainHandler = new Handler(){
            public void handleMessage(Message msg){
                //detail1.setBookText((String)msg.obj);
                result = (String)msg.obj;
                if(onProgressListener != null){
                    System.out.println("==========callback function: set the textView text");
                    //调用Activity中的onProgress方法，修改UI
                    onProgressListener.onProgress((String)msg.obj);
                }
                
                System.out.println("==========main thread get the message:"+msg.obj);
                System.out.println("Finally, the message is :"+msg.obj);
                
            }
        };
        
        QueryThread thread = new QueryThread();
        thread.start();
        
        while(mChildHandler == null){
            
        }
        if(mChildHandler != null){
            //将mChildHandler加入到消息队列中
            Message childMsg = mChildHandler.obtainMessage();
            childMsg.obj = mMainHandler.getLooper().getThread().getName();
            System.out.println("==========send message to mChild: "+childMsg.obj);
            mChildHandler.sendMessage(childMsg);
        }
    }
    
    //设置回调函数的接口。Activity通过这个方法获取对象
    public void setOnProgressListener(OnProgressListener onProgressListener){
        this.onProgressListener = onProgressListener;
    }
    
    
    public void onDestroy(){
        super.onDestroy();
        mChildHandler.getLooper().quit();
    }
    public String getBookDetails(int id){
        
        StringBuilder result = new StringBuilder();
        String urlStr = "http://192.168.1.21:8080/servletTest/test";
        HttpPost post = new HttpPost(urlStr);
        
        try{

            JSONObject json = new JSONObject();
            json.put("book_id", id);
            System.out.println("=============="+json.toString());
            
            StringEntity se = new StringEntity(json.toString());
            se.setContentEncoding((Header) new BasicHeader(HTTP.CONTENT_TYPE, "application/json"));
            post.setEntity(se);
            
            HttpClient httpClient = getHttpClient();
            HttpResponse httpResponse = httpClient.execute(post);

            int httpCode = httpResponse.getStatusLine().getStatusCode();
            if(httpCode==HttpURLConnection.HTTP_OK && httpResponse != null){
                HttpEntity entity = httpResponse.getEntity();
                InputStream inputStream = entity.getContent();
                InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
                BufferedReader reader = new BufferedReader(inputStreamReader);
                String s;
                while((s=reader.readLine()) != null){
                    result.append(s);
                }
                reader.close();
                
                JSONObject object =  new JSONObject(result.toString());
                String str = object.getString("book_list");
                //detail1.setBookText(str);

                return str;
            }
            
        }catch(Exception exception){
            exception.printStackTrace();
        }
        return null;
    }
    
    public HttpClient getHttpClient(){
    BasicHttpParams httpParams = new BasicHttpParams();
    HttpConnectionParams.setConnectionTimeout(httpParams, 5*1000);
    HttpConnectionParams.setSoTimeout(httpParams, 10*1000);
    HttpClient client = new DefaultHttpClient(httpParams);
    return client;
}

    class QueryThread extends Thread{
        public void run(){

            //初始化消息循环队列，需要在Handler创建之前
            Looper.prepare();
            mChildHandler = new Handler(){
                public void handleMessage(Message msg){
                    //访问网络等耗时工作
                    String book_titleString = getBookDetails(id);
                    System.out.println("================book_title from servlet is "+book_titleString);
                    Message toMain = mMainHandler.obtainMessage();
                    toMain.obj = book_titleString;
                    //向主线程当前线程的Looper对发送message
                    System.out.println("================send message to main thread: "+book_titleString);
                    mMainHandler.sendMessage(toMain);
                }
            };
            //启动子线程消息循环队列
            Looper.loop();
            System.out.println("================json is done!");
        }
    }
    
    public class MsgBinder extends Binder{
        public MsgService getService(){
            
            return MsgService.this;
        }
    }
    
    public int getIndex(){
        System.out.println("greg");
        return index;
    }
    
    public void startDonwload(){
        new Thread(new Runnable() {
            
            @Override
            public void run() {
                // TODO Auto-generated method stub
                index++;
                System.out.println("fd");
            }
        }).start();
    }
    
    

    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        return new MsgBinder();
    }
}

Bon Appetite~