Android之異步任務AsyncTask解析Json數據

一、服務器端生成json數據

①在eclipse中創建Web->Dynamic web Project 工程名命爲Web_AsyncTask_Json。

②創建CityAction.java類（Servlet類）。此時會出錯，原因是servlet-api.jar沒有導入工程中，步驟如下：

工程名右鍵->Properties->Java Build Path->Libraries->Add External JARS->找到Apache-tomcat-7.0.34文件中lib文件夾下的servlet-api.jar（D:\java2EE\apache-tomcat-7.0.34\lib\servlet-api.jar）選中->打開->ok

package com.city.action;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import net.sf.json.JSONSerializer;

/**
 * Servlet implementation class CityAction
 */
@WebServlet("/CityAction")
public class CityAction extends HttpServlet {
	private static final long serialVersionUID = 1L;

    /**
     * Default constructor. 
     */
    public CityAction() {
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		this.doPost(request, response);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		response.setCharacterEncoding("utf-8");
		request.setCharacterEncoding("utf-8");
		PrintWriter writer=response.getWriter();
		List<String> list=CityDataSource.getCitysList();//生成json對象,json數據一定要帶<K,V>
		Map<String, List<String>>map=new HashMap<String, List<String>>();
		map.put("citys", list);
		String jsonString=JSONSerializer.toJSON(map).toString();
		writer.println(jsonString);//注意生成json字符串時，這個地方一定要是獨立乾淨的
		writer.flush();
		writer.close();
	}

}

doPost()方法中還可以這樣寫

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html;charset=utf-8");
		response.setCharacterEncoding("utf-8");
		request.setCharacterEncoding("utf-8");
		PrintWriter writer=response.getWriter();
		String type=request.getParameter("type");
		if(type.equals("json")){
			List<String> list=CityDataSource.getCitysList();//生成json對象,json數據一定要帶<K,V>
			Map<String, List<String>>map=new HashMap<String, List<String>>();
			map.put("citys", list);
			String jsonString=JSONSerializer.toJSON(map).toString();
			writer.println(jsonString);//注意生成json字符串時，這個地方一定要是獨立乾淨的
		}
		
		writer.flush();
		writer.close();
	}

如果按上面的寫法，對應的MainActivity.java中的CITY_PATH

private final String CITY_PATH="http://192.168.1.100:8080/Web_AsyncTask_Json/CityAction?type=json";

③提供簡單的數據源：聲明一個類CityDataSource.java

當用到JSONSerializer類時，要引入包json-lib-2.2.2-jdk15.jar，步驟如下：

把json-lib-2.2.2-jdk15.jar複製粘貼到工程文件下lib文件夾中刷新

package com.city.action;

import java.util.ArrayList;
import java.util.List;

public class CityDataSource {

	public CityDataSource() {
		// TODO Auto-generated constructor stub
	}
	
	/**
	 * 提供數據源
	 * @return
	 */
	public static List<String> getCitysList(){
		List<String> list=new ArrayList<String>();
		list.add("北京");
		list.add("上海");
		list.add("廣州");
		list.add("深圳");
		return list;
	}
}

④啓動tomcat（正常啓動），在地址欄輸入Ip地址http://192.168.1.100:8080/Web_AsyncTask_Json/CityAction回車

可能出現錯誤：HTTP Status 500-Servlet exection threw an exception

解決：把commons-beanutils-1.7.jar
commons-lang.jar
ezmorph.jar

複製粘貼到lib中，此時還會報錯，導入（不是複製粘貼）commons-collections.jar
commons-logging-1.1.1.jar

導入步驟：工程名右鍵->Properties->Java Build Path->Libraries->Add External JARS->找到工程文件中lib文件夾下的commons-collections.jar和commons-logging-1.1.1.jar選中->打開->ok

問題解決，運行顯示json數據

{"citys":["北京","上海","廣州","深圳"]}

二、Android手機客戶端取出json數據

①添加網絡授權，步驟如下

AndroidManifest.xml->單擊Permission->單擊Add->選中uses-permission ->在Name中找到INTERNET->點擊下面的AndroidManifest.xml保存

②把數據展現在Spinner中，在activity_main.xml中

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.android_asynctask_json.MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="31dp"
        android:layout_marginTop="102dp"
        android:textSize="20sp"
        android:text="所屬城市:" />

    <Spinner
        android:id="@+id/spinner1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/textView1"
        android:layout_marginLeft="14dp"
        android:layout_toRightOf="@+id/textView1" />
    
</RelativeLayout>

③新建一個包com.example.android_asynctask_json.http，創建http工具類HttpUtils.java

package com.example.android_asynctask_json.http;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;

public class HttpUtils {

	public HttpUtils() {
		// TODO Auto-generated constructor stub
	}
	
	/**
	 * 
	 * @param path  獲取指定路徑的json信息
	 * @param encoding  指定編碼格式
	 * @return
	 */
	public static String sendPostMethod(String path,String encoding){
		String result="";
		HttpClient httpClient=new DefaultHttpClient();
		try {
			HttpPost post=new HttpPost(path);
			HttpResponse response=httpClient.execute(post);
			if(response.getStatusLine().getStatusCode()==200){
				result=EntityUtils.toString(response.getEntity(), encoding);
			}
			
		} catch (Exception e) {
			// TODO: handle exception
			e.printStackTrace();
		}finally{
			httpClient.getConnectionManager().shutdown();//關閉連接
		}
		return result;
		
	}
}

④新建一個包com.example.android_asynctask_json.json，創建一個json工具類JsonTools.java

package com.example.android_asynctask_json.json;

import java.util.ArrayList;
import java.util.List;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

public class JsonTools {

	public JsonTools() {
		// TODO Auto-generated constructor stub
	}
	
	public static List<String> parseList(String jsonString){
		List<String> list=new ArrayList<String>();
		try {
			JSONObject jsonObject=new JSONObject(jsonString);//得到 {"citys":["北京","上海","廣州","深圳"]} 這個大對象
			JSONArray jsonArray=jsonObject.getJSONArray("citys");
			for(int i=0;i<jsonArray.length();i++){
				list.add(jsonArray.getString(i));
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return list;
	}
}

MainActivity.java

package com.example.android_asynctask_json;

import java.util.List;

import com.example.android_asynctask_json.http.HttpUtils;
import com.example.android_asynctask_json.json.JsonTools;

import android.support.v7.app.ActionBarActivity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ArrayAdapter;
import android.widget.Spinner;

public class MainActivity extends ActionBarActivity {

	private Spinner spinner1;
	private final String CITY_PATH="http://192.168.1.100:8080/Web_AsyncTask_Json/CityAction";
	private ArrayAdapter<String> adapter;
	private ProgressDialog dialog;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		spinner1=(Spinner) this.findViewById(R.id.spinner1);//加載Spinner控件
		//adapter=new ArrayAdapter<String>(context, resource, textViewResourceId);
		//spinner1.setAdapter(adapter);//這句話執行完之後，數據就已經有了，所以這行代碼應該在另外一個線程中實現，然後再更新UI
		dialog=new ProgressDialog(MainActivity.this);
		dialog.setTitle("提示");
		dialog.setMessage("正在加載...");
		new MyTask().execute(CITY_PATH);//執行異步任務
		
	}

	class MyTask extends AsyncTask<String, Void, List<String>>{

		@Override
		protected void onPreExecute() {
			// TODO Auto-generated method stub
			super.onPreExecute();
			dialog.show();
		}
		
		@Override
		protected void onPostExecute(List<String> result) {
			// TODO Auto-generated method stub
			super.onPostExecute(result);
			adapter=new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_dropdown_item, result);//構建適配器
			spinner1.setAdapter(adapter);
			dialog.dismiss();
		}
		
		/**
		 * 注意：在做Android開發過程中HttpUtils和JsonTools工具類是必須要有的
		 * 在一個項目中json數據格式有可能有四到五種，所以工具類裏的方法要有四到五個方法來解析
		 */
		@Override
		protected List<String> doInBackground(String... params) {
			// TODO Auto-generated method stub
			List<String> list=null;
			String jsonString=HttpUtils.sendPostMethod(params[0], "utf-8");
			list=JsonTools.parseList(jsonString);
			return list;
		}
		//List<String>這個結果表示json解析之後的結果，結果會很快塞到適配器當中
	}
	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}

運行效果圖如下

Android之異步任務AsyncTask解析Json數據

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