Java Gson JSONObject 基本用法(Json解析用)

JSONObject JSONArray

import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;

	// 生成json字符串
	JSONArray jSONArray = JSONArray.parseArray("[\"AAA\",\"BBB\"]");
	System.out.println(jSONArray.getString(0));  // AAA
	
	// 生成json字符串
    JSONObject json = new JSONObject();
    json.put("id", 100);
    json.put("name", "Tony");
    String params = json.toString();
    // 生成一般对象
    UserInfo user = json.toJavaObject(UserInfo.class);
    System.out.println(user.getName());  // Tony

// 将json字符串生成JSONObject和JSONArray
String jsonStr = "{\"balances\":"
        + "[{\"asset\":\"AAA\",\"free\":\"0.00000000\",\"locked\":\"0.00000000\"},"
        + "{\"asset\":\"BBB\",\"free\":\"0.00000000\",\"locked\":\"0.00000000\"},"
        + "{\"asset\":\"CCC\",\"free\":\"0.00000000\",\"locked\":\"0.00000000\"},"
        + "{\"asset\":\"DDD\",\"free\":\"0.00000000\",\"locked\":\"0.00000000\"},"
        + "{\"asset\":\"EEE\",\"free\":\"0.00000000\",\"locked\":\"0.00000000\"}"
        + "]}";
JSONObject jsonData = JSONObject.parseObject(jsonStr);
JSONArray jsonArr = jsonData.getJSONArray("balances");
List<Balance> balances = jsonArr.toJavaList(Balance.class);

Gson

• 反序列化：解析Json

    Gson gson = new Gson();
    
    // 一般对象
    TradeInfo trade = gson.fromJson("{\"id\":18, \"value\":\"xxxx\"}", TradeInfo.class);
    System.out.println(trade.getValue());  // xxxx
    
    // String对象
    String str = gson.fromJson("{\"value\":\"xxxx\"}", String.class);
    System.out.println(str);  // ? 错了
    
    // 整数对象
    int i = gson.fromJson("{\"id\":18}", int.class);
    System.out.println(i);  // ? 错了
    
    // 数组对象
    String[] strs = gson.fromJson("[\"Android\",\"Java\",\"PHP\"]", String[].class);
    System.out.println(strs);  // Android

    // List对象01
    List<String> strList = gson.fromJson("[\"Android\",\"Java\",\"PHP\"]", new TypeToken<List<String>>() {}.getType());
    System.out.println(strList.get(0));  // Android
    
    // List对象02
    List<String[]> strList = gson.fromJson("[[\"Android\"],[\"Java\"],[\"PHP\"]]", new TypeToken<List<String[]>>() {}.getType());
    System.out.println(strList.get(0)[0]);  // Android

    // 复杂数组对象01
	public class TestRecord {
	    public List<String[]> bids;
	}
    TestRecord tr = gson.fromJson("{\"bids\":[[\"AAA\",\"BBB\"],[\"CCC\",\"DDD\"]]}", TestRecord.class);  // 用 new TypeToken<TestRecord>(){}.getType()) 也行。
    System.out.println(tr.bids.get(0)[0]);  // AAA

	// Map对象
	String jsonStr = "{\"name\":{\"asks\":[[\"AAA\",\"BBB\"],[\"CCC\",\"DDD\"]]}}";
	Map<String, OrderBook> map = gson.fromJson(jsonStr, new TypeToken<Map<String, OrderBook>>(){}.getType());
	System.out.println(map.get("name").asks.get(0)[0]);  // AAA
	
    // TypeToken 的构造方法是protected修饰的,所以上面才会写成new TypeToken<List<String>>() {}.getType() 而不是 new TypeToken<List<String>>().getType()

• 序列化：生成Json

    Gson gson = new Gson();
    
    // 一般对象
    TradeInfo trade = new TradeInfo(18, "xxxx");
    String jsonStr = gson.toJson(trade);
    
    // String对象
    String jsonStr = gson.toJson("xxxx");

    // 整数对象
    int jsonStr = gson.toJson(18);

	// Map对象
	public class OrderBook {
    	public List<String[]> asks;
	}
	
    String[] strs1 = {"AAA","BBB"};
    String[] strs2 = {"CCC","DDD"};
    
    OrderBook orderBook = new OrderBook();
    orderBook.asks = new ArrayList<String[]>();
    orderBook.asks.add(strs1);
    orderBook.asks.add(strs2);

    Map<String, OrderBook> map = new HashMap<String, OrderBook>();
    map.put("name", orderBook);
    
    String jsonStr = gson.toJson(map);
    System.out.println(jsonStr);  // {"name":{"asks":[["AAA","BBB"],["CCC","DDD"]]}}

• 依赖包

<!-- pom.xml -->
        <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
        </dependency>
        <!--
        	在Spring boot中已经有限定，不用设置version。
        	<version>2.2.8</version>
        -->

• 资料
  高阶 GSON搞定任何形式JSON数组
  基本 JSON对象相互转换
  Java 中 Gson的使用
  Gson在Java中的使用实例