无涯教程-JSON - Java编程

无涯教程
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本章介绍如何使用Java编程语言编码和解码JSON对象。让我们从准备环境开始，开始使用Java for JSON进行编程。

在开始使用Java编码和解码JSON之前,您需要安装任何可用的JSON模块，在本教程中,我们已经下载并安装了JSON.simple,并具有将 json-simple-1.1.1.jar 文件的位置添加到环境变量CLASSPATH中。

JSON和Java映射

JSON.simple在解码或解析时将实体从左侧映射到右侧，并在编码时将实体从右侧映射到左侧。

JSON Java
string java.lang.String
number java.lang.Number
true | false java.lang.Boolean
null null
array java.util.List
Object java.util.Map

在解码时，java.util.List的默认具体类为org.json.simple.JSONArray，而java.util.Map的默认具体类为org.json.simple.JSONObject。

编码JSON

以下是使用Java JSONObject编码JSON对象的简单示例，Java JSONObject是java.util.HashMap的子类。如果需要严格的元素排序，请使用JSONValue.toJSONString(map)方法和有序映射实现(例如java.util.LinkedHashMap)。

import org.json.simple.JSONObject;

class JsonEncodeDemo {


public static void main(String[] args) {
JSONObject obj = new JSONObject();


  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"name"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"learnfk"</span><span class="pun">);</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"num"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Integer</span><span class="pun">(</span><span class="lit">100</span><span class="pun">));</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"balance"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Double</span><span class="pun">(</span><span class="lit">1000.21</span><span class="pun">));</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"is_vip"</span><span class="pun">,</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Boolean</span><span class="pun">(</span><span class="kwd">true</span><span class="pun">));</span><span class="pln">

  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="pln">obj</span><span class="pun">);</span><span class="pln">



}
}

在编译并执行上述程序时，将产生以下输出-

{"balance": 1000.21, "num":100, "is_vip":true, "name":"learnfk"}

以下是显示使用Java JSONObject进行JSON对象流传输的另一个示例-

import org.json.simple.JSONObject;

class JsonEncodeDemo {


public static void main(String[] args) {


  </span><span class="typ">JSONObject</span><span class="pln"> obj </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">JSONObject</span><span class="pun">();</span><span class="pln">

  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"name"</span><span class="pun">,</span><span class="str">"learnfk"</span><span class="pun">);</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"num"</span><span class="pun">,</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Integer</span><span class="pun">(</span><span class="lit">100</span><span class="pun">));</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"balance"</span><span class="pun">,</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Double</span><span class="pun">(</span><span class="lit">1000.21</span><span class="pun">));</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">put</span><span class="pun">(</span><span class="str">"is_vip"</span><span class="pun">,</span><span class="kwd">new</span><span class="pln"> </span><span class="typ">Boolean</span><span class="pun">(</span><span class="kwd">true</span><span class="pun">));</span><span class="pln">

  </span><span class="typ">StringWriter</span><span class="pln"> </span><span class="kwd">out</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">StringWriter</span><span class="pun">();</span><span class="pln">
  obj</span><span class="pun">.</span><span class="pln">writeJSONString</span><span class="pun">(</span><span class="kwd">out</span><span class="pun">);</span><span class="pln">
  
  </span><span class="typ">String</span><span class="pln"> jsonText </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">out</span><span class="pun">.</span><span class="pln">toString</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="pln">jsonText</span><span class="pun">);</span><span class="pln">



}
}

在编译并执行上述程序时，将产生以下输出-

{"balance": 1000.21, "num":100, "is_vip":true, "name":"learnfk"}

解码JSON

下面的示例使用 JSONObject 和 JSONArray ，其中JSONObject是java.util.Map，而JSONArray是java.util.List，因此您可以使用标准操作来访问Map或列表。

import org.json.simple.JSONObject;
import org.json.simple.JSONArray;
import org.json.simple.parser.ParseException;
import org.json.simple.parser.JSONParser;

class JsonDecodeDemo {


public static void main(String[] args) {


  </span><span class="typ">JSONParser</span><span class="pln"> parser </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="typ">JSONParser</span><span class="pun">();</span><span class="pln">
  </span><span class="typ">String</span><span class="pln"> s </span><span class="pun">=</span><span class="pln"> </span><span class="str">"[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]"</span><span class="pun">;</span><span class="pln">
	
  </span><span class="kwd">try</span><span class="pun">{</span><span class="pln">
     Object </span><span class="pln">obj </span><span class="pun">=</span><span class="pln"> parser</span><span class="pun">.</span><span class="pln">parse</span><span class="pun">(</span><span class="pln">s</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">JSONArray</span><span class="pln"> array </span><span class="pun">=</span><span class="pln"> </span><span class="pun">(</span><span class="typ">JSONArray</span><span class="pun">)</span><span class="pln">obj</span><span class="pun">;</span><span class="pln">
		
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"The 2nd element of array"</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">array</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="lit">1</span><span class="pun">));</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">();</span><span class="pln">

     </span><span class="typ">JSONObject</span><span class="pln"> obj2 </span><span class="pun">=</span><span class="pln"> </span><span class="pun">(</span><span class="typ">JSONObject</span><span class="pun">)</span><span class="pln">array</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="lit">1</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Field\"1\""</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">obj2</span><span class="pun">.</span><span class="kwd">get</span><span class="pun">(</span><span class="str">"1"</span><span class="pun">));</span><span class="pln">    

     s </span><span class="pun">=</span><span class="pln"> </span><span class="str">"{}"</span><span class="pun">;</span><span class="pln">
     obj </span><span class="pun">=</span><span class="pln"> parser</span><span class="pun">.</span><span class="pln">parse</span><span class="pun">(</span><span class="pln">s</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">obj</span><span class="pun">);</span><span class="pln">

     s </span><span class="pun">=</span><span class="pln"> </span><span class="str">"[5,]"</span><span class="pun">;</span><span class="pln">
     obj </span><span class="pun">=</span><span class="pln"> parser</span><span class="pun">.</span><span class="pln">parse</span><span class="pun">(</span><span class="pln">s</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">obj</span><span class="pun">);</span><span class="pln">

     s </span><span class="pun">=</span><span class="pln"> </span><span class="str">"[5,,2]"</span><span class="pun">;</span><span class="pln">
     obj </span><span class="pun">=</span><span class="pln"> parser</span><span class="pun">.</span><span class="pln">parse</span><span class="pun">(</span><span class="pln">s</span><span class="pun">);</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">obj</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="kwd">catch</span><span class="pun">(</span><span class="typ">ParseException</span><span class="pln"> pe</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
	
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"position: "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> pe</span><span class="pun">.</span><span class="pln">getPosition</span><span class="pun">());</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="pln">pe</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">



}
}

在编译并执行上述程序时，将产生以下输出-

The 2nd element of array
{"1":{"2":{"3":{"4":[5,{"6":7}]}}}}

Field "1"
{"2":{"3":{"4":[5,{"6":7}]}}}
{}
[5]
[5,2]

参考链接

www.learnfk.com/json/json-j…

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