一、什么是json
json(Javascript Object Notation)是一种轻量级的数据交换格式,相比于xml这种数据交换格式来说,因为解析xml比较的复杂,而且需要编写大段的代码,所以客户端和服务器的数据交换格式往往通过json来进行交换。尤其是对于web开发来说,json数据格式在客户端直接可以通过javascript来进行解析。
json一共有两种数据结构,一种是以 (key/value)对形式存在的无序的jsonObject对象,一个对象以“{”(左花括号)开始,“}”(右花括号)结束。每个“名称”后跟一个“:”(冒号);“‘名称/值’ 对”之间使用“,”(逗号)分隔。
例如:{"name": "xiaoluo"}, 这就是一个最简单的json对象,对于这种数据格式,key值必须要是string类型,而对于value,则可以是string、number、object、array等数据类型
另一种数据格式就是有序的value的集合,这种形式被称为是jsonArray,数组是值(value)的有序集合。一个数组以“[”(左中括号)开始,“]”(右中括号)结束。值之间使用“,”(逗号)分隔。
二.下面介绍一个例子(该例子也是借鉴网友的:附近地址:http://www.cnblogs.com/xiaoluo501395377/p/3446605.html)
1. 首先上结果图
简单的布局显示,第二幅图是要根据服务器的数据返回后显示出来的.
图一: 图二:
图一是服务端的文件,图二是客户端的文件
2. 首先看服务器上的代码
1 package com.bing.test; 2 import java.io.IOException; 3 import java.io.PrintWriter; 4 import java.util.ArrayList; 5 import java.util.HashMap; 6 import java.util.List; 7 import java.util.Map; 8 9 import javax.servlet.ServletException; 10 import javax.servlet.http.HttpServlet; 11 import javax.servlet.http.HttpServletRequest; 12 import javax.servlet.http.HttpServletResponse; 13 14 import com.alibaba.fastjson.JSON; 15 16 17 public class CityServlet extends HttpServlet{ 18 19 /** 20 */ 21 private static final long serialVersionUID = 1L; 22 23 public CityServlet(){ 24 super(); 25 } 26 27 protected void doGet(HttpServletRequest request, 28 HttpServletResponse response) throws ServletException, IOException 29 { 30 this.doPost(request, response); 31 } 32 33 protected void doPost(HttpServletRequest request, 34 HttpServletResponse response) throws ServletException, IOException 35 { 36 37 response.setContentType("text/html;charset=utf-8"); 38 request.setCharacterEncoding("utf-8"); 39 response.setCharacterEncoding("utf-8"); 40 41 PrintWriter writer = response.getWriter(); 42 43 String type = request.getParameter("type"); 44 if("json".equals(type)){ 45 List<String> city = new ArrayList<String>(); 46 city.add("上海"); 47 city.add("北京"); 48 city.add("重庆"); 49 city.add("四川"); 50 city.add("黑龙江"); 51 52 Map<String, List<String>> map = new HashMap<String, List<String>>(); 53 map.put("cities", city); 54 55 String cityString = JSON.toJSONString(map); 56 writer.println(cityString); 57 58 // response.sendRedirect("index3.jsp"); 59 60 } 61 writer.flush(); 62 writer.close(); 63 64 } 65 66 67 68 }
如果客户端请求的参数是type=json,则响应给客户端一个json数据格式
不过其中String cityString = JSON.toJSONString(map); JSON类需要用到图一中的一个jar包(WEB-INF/lib/下的fastjson-1.2.4.jar),是ali推出的.用着不错.
下面来看一下关于客户端的代码
(1).首先是样式布局
1 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 2 xmlns:tools="http://schemas.android.com/tools" 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 tools:context="com.example.jsontest.MainActivity" > 6 7 <Spinner 8 android:id="@+id/city_show" 9 android:layout_width="wrap_content" 10 android:layout_height="wrap_content" 11 android:layout_alignParentTop="true" 12 android:layout_marginTop="50dp" 13 android:layout_centerInParent="true"/> 14 15 <Button 16 android:id="@+id/showBtn" 17 android:layout_width="wrap_content" 18 android:layout_height="wrap_content" 19 android:layout_alignParentBottom="true" 20 android:layout_marginBottom="50dp" 21 android:layout_centerInParent="true" 22 android:text="@string/show"/> 23 24 25 </RelativeLayout>
布局文件so easy,没有什么好说的
(2). 然后是MainActivity
1 package com.example.jsontest; 2 3 import java.util.ArrayList; 4 import java.util.List; 5 6 import android.app.Activity; 7 import android.app.Dialog; 8 import android.app.ProgressDialog; 9 import android.os.Bundle; 10 import android.os.Handler; 11 import android.os.Message; 12 import android.view.View; 13 import android.widget.ArrayAdapter; 14 import android.widget.Button; 15 import android.widget.SimpleAdapter; 16 import android.widget.Spinner; 17 18 19 public class MainActivity extends Activity { 20 21 public static final int LOADING_DOWN = 0x0001; 22 23 private List<String> city = new ArrayList<String>(); 24 25 private final String CITY_PATH_JSON = "http://10.1.8.142:8080/JSONTest/city?type=json"; 26 27 private Spinner spinner; 28 private Button showBtn; 29 30 private ProgressDialog dialog; 31 32 public Handler handler = new Handler(){ 33 @Override 34 public void handleMessage(Message msg) { 35 36 switch (msg.what) { 37 case LOADING_DOWN: 38 city = (List<String>) msg.obj; 39 showContent(); 40 break; 41 default: 42 break; 43 } 44 } 45 }; 46 47 48 49 @Override 50 protected void onCreate(Bundle savedInstanceState) { 51 super.onCreate(savedInstanceState); 52 setContentView(R.layout.activity_main); 53 54 initView(); 55 56 } 57 58 private void initView(){ 59 60 showBtn = (Button) findViewById(R.id.showBtn); 61 spinner = (Spinner) findViewById(R.id.city_show); 62 63 dialog = new ProgressDialog(this); 64 } 65 66 67 @Override 68 protected void onStart() { 69 super.onStart(); 70 71 if(city.size() == 0){ 72 city.add("城市"); 73 }else{ 74 75 } 76 77 spinner.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, city)); 78 spinner.setSelection(0); 79 80 showBtn.setOnClickListener(new Button.OnClickListener() { 81 @Override 82 public void onClick(View view) { 83 showCity(); 84 } 85 }); 86 87 } 88 89 private void showCity(){ 90 91 new MyAsyncTask(MainActivity.this, dialog).execute(CITY_PATH_JSON); 92 93 } 94 95 96 private void showContent(){ 97 98 spinner.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, city)); 99 spinner.setSelection(0); 100 } 101 102 103 }
private final String CITY_PATH_JSON = "http://10.1.8.142:8080/JSONTest/city?type=json"; IP地址换成自己本机上tomcat运行时的IP
然后是几个其它工具类等等
1. MyAsyncTast.java类 异步线程处理
1 package com.example.jsontest; 2 3 import java.io.IOException; 4 import java.util.ArrayList; 5 import java.util.List; 6 7 import android.R.integer; 8 import android.app.ProgressDialog; 9 import android.content.Context; 10 import android.os.AsyncTask; 11 import android.os.Message; 12 import android.util.Log; 13 14 import com.bing.tool.HttpUtils2; 15 import com.bing.tool.JsonUtils; 16 17 public class MyAsyncTask extends AsyncTask<String, integer, List<String>> { 18 19 private static final String TAG = "MyAsyncTask"; 20 21 public static final int LOADING_DOWN = 0x0001; 22 23 private List<String> result = new ArrayList<String>(); 24 25 private MainActivity activity; 26 27 private ProgressDialog dialog; 28 29 public MyAsyncTask(Object obj){ 30 31 if(obj instanceof ProgressDialog){ 32 this.dialog = (ProgressDialog)obj; 33 } 34 } 35 36 public MyAsyncTask(MainActivity activity, Object obj){ 37 38 if(obj instanceof ProgressDialog){ 39 this.dialog = (ProgressDialog)obj; 40 } 41 42 if(activity instanceof MainActivity){ 43 this.activity = activity; 44 } 45 } 46 47 48 @Override 49 protected void onPreExecute() { 50 51 showDialog(); 52 } 53 54 private void showDialog(){ 55 dialog.show(); 56 dialog.setTitle("提示信息"); 57 dialog.setMessage("loading......"); 58 dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); 59 dialog.setCancelable(false); 60 } 61 62 @Override 63 protected List<String> doInBackground(String... arg0) { 64 65 try { 66 Log.i(TAG, "back content: " + arg0[0]); 67 String content = HttpUtils2.sendPostMessage(arg0[0], "UTF-8"); 68 69 Log.i(TAG, "back content: " + content); 70 result = JsonUtils.parseJsonContent(content); 71 72 } catch (IOException e) { 73 e.printStackTrace(); 74 } 75 76 return result; 77 } 78 79 80 @Override 81 protected void onPostExecute(List<String> result) { 82 83 Message msg = new Message(); 84 msg.what = LOADING_DOWN; 85 msg.obj = result; 86 activity.handler.sendMessage(msg); 87 dialog.dismiss(); 88 89 } 90 91 92 }
2. JsonUtils.java 类,用于处理JSONObject
1 package com.bing.tool; 2 3 import java.util.ArrayList; 4 import java.util.List; 5 6 import org.json.JSONArray; 7 import org.json.JSONException; 8 import org.json.JSONObject; 9 10 public class JsonUtils { 11 12 13 /** 14 * @param content 15 * @return 16 */ 17 public static List<String> parseJsonContent(String content){ 18 19 List<String> contents = new ArrayList<String>(); 20 21 JSONObject jsonObj; 22 try { 23 jsonObj = new JSONObject(content); 24 25 JSONArray jsonArray = jsonObj.getJSONArray("cities"); 26 27 for(int i = 0; i < jsonArray.length(); i++){ 28 29 contents.add(jsonArray.getString(i)); 30 } 31 32 }catch (JSONException e) { 33 e.printStackTrace(); 34 } 35 36 return contents; 37 38 } 39 40 41 }
3. HttpUtils2.java类,用于请求报务器获取所得的数据
1 package com.bing.tool; 2 3 import java.io.IOException; 4 import java.io.InputStreamReader; 5 6 import org.apache.http.HttpEntity; 7 import org.apache.http.HttpResponse; 8 import org.apache.http.HttpStatus; 9 import org.apache.http.client.ClientProtocolException; 10 import org.apache.http.client.HttpClient; 11 import org.apache.http.client.methods.HttpGet; 12 import org.apache.http.impl.client.DefaultHttpClient; 13 import org.apache.http.util.EntityUtils; 14 15 import android.util.Log; 16 17 public class HttpUtils2 { 18 19 public static String sendPostMessage(String url, String encode) throws IOException{ 20 21 String result = null; 22 HttpGet request = new HttpGet(url); 23 HttpClient httpClient = new DefaultHttpClient(); 24 25 try { 26 HttpResponse response = httpClient.execute(request); 27 if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){ 28 Log.i("here", "here"); 29 HttpEntity httpEntity = response.getEntity(); 30 if(httpEntity != null){ 31 result = EntityUtils.toString(httpEntity); 32 Log.i("result", "result: " + result); 33 } 34 } 35 36 }catch (Exception e) { 37 e.printStackTrace(); 38 }finally{ 39 httpClient.getConnectionManager().shutdown(); 40 } 41 42 return result; 43 44 } 45 46 47 }
4. AndoridMainfest.xml
当然别往了开启我们的网络授权
<uses-permission android:name="android.permission.INTERNET"/>
5. 运行程序
跑程序,就可以完成了客户端与服务器端通过json来进行数据的交换
在这过程中遇到一些问题:
1. at org.apache.catalina.loader.WebappClassLoader.loadClass. 就是关于导包的问题
过程中不知什么原因,不过将包放在WEB-INF/lib/下,然后build bath就可以了.
新手学android,大部分内容都是照搬的,不过其中过程中还是费了一点时间,如果觉得该文章太浅蒲,勿喷,谢谢
来源:https://www.cnblogs.com/bingofworld/p/4589281.html