java json处理

布满荆棘的人生 2021-09-23 15:32 338阅读 0赞

com.alibaba.fastjson  
引入依赖包

<dependency>
    			<groupId>com.alibaba</groupId>
    			<artifactId>fastjson</artifactId>
    			<version>1.2.9</version>
    		</dependency>

直接上最终代码

package yyst.myTest.jsonTest;
    
    import java.util.HashMap;
    import java.util.Map;
    
    import com.alibaba.fastjson.JSONObject;
    import com.alibaba.fastjson.serializer.SerializerFeature;
    import com.alibaba.fastjson.serializer.ValueFilter;
    
    public class FjTest { 
    
    	public static void main(String[] args) { 
    		// TODO Auto-generated method stub
    		Map < String , Object > jsonMap = new HashMap< String , Object>();  
    		jsonMap.put("c", "21");
    		jsonMap.put("d", "");
    		jsonMap.put("e", null);
    		
    		System.out.println(JSONObject.toJSONString(jsonMap));
    		System.out.println(JSONObject.toJSONString(new FjBean()));
    		System.out.println();
    		System.out.println(JSONObject.toJSONString(jsonMap, SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty));
    		System.out.println(JSONObject.toJSONString(new FjBean(), SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty));
    		System.out.println();
    		ValueFilter valueFilter = new ValueFilter() { 
    
    			@Override
    			public Object process(Object object, String name, Object value) { 
    				// TODO Auto-generated method stub
    // System.out.println(object);
    // System.out.println(name);
    // System.out.println(value);
    				return value == null ? "" : value;
    			}
    			
    		};
    		System.out.println(JSONObject.toJSONString(jsonMap, valueFilter));
    		
    		System.out.println("\r\nstring to object");
    		System.out.println(JSONObject.parseObject(JSONObject.toJSONString(jsonMap, valueFilter), Map.class));
    		System.out.println(JSONObject.parseObject(JSONObject.toJSONString(new FjBean(), SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty), FjBean.class));
    	}
    
    }
    
    class FjBean{ 
    	public String a1 = "a";
    	public String a2 = null;
    	public String getA1() { 
    		return a1;
    	}
    	public void setA1(String a1) { 
    		this.a1 = a1;
    	}
    	public String getA2() { 
    		return a2;
    	}
    	public void setA2(String a2) { 
    		this.a2 = a2;
    	}
    	
    }

输出

{"c":"21","d":""}
    {"a1":"a"}
    
    {"c":"21","d":"","e":null}
    {"a1":"a","a2":""}
    
    {"c":"21","d":"","e":""}
    
    string to object
    {c=21, d=, e=}
    yyst.myTest.jsonTest.FjBean@15615099

特别说明一下null值的处理。默认情况下，如果值为null，将不会输出。这在与其它语言的交互中非常容易出现bug。根据个人经验，转成空字符串可以适应更多的场景。上面代码中，通过加入`SerializerFeature.WriteMapNullValue, SerializerFeature.WriteNullStringAsEmpty` ，可以处理bean的情况。  
但是当处理对象为Map时，无法正确转换。网上有不少Map处理的示例，但是都无法重现，有可能是版本问题，因为我在1.2.9的源码中未发现相关处理（读的不全，如有错误欢迎指正）。因此使用了自定义过滤器的方法。  
[https://github.com/alibaba/fastjson/wiki/ContextValueFilter][https_github.com_alibaba_fastjson_wiki_ContextValueFilter]

[https_github.com_alibaba_fastjson_wiki_ContextValueFilter]: https://github.com/alibaba/fastjson/wiki/ContextValueFilter