json串和实体类字段不一致的情况的测试

一时失言乱红尘 2022-04-02 13:56 384阅读 0赞

这里我们对json串和实体类字段不一致的情况进行一个测试：

首先，我们建立一个实体类：这里简单定义了name,sex,age三个属性，以及get set tostring方法。

public class Student { 
    	private String name;
    	private String sex;
    	private Integer age;
    	public String getName() { 
    		return name;
    	}
    	public String getSex() { 
    		return sex;
    	}
    	public Integer getAge() { 
    		return age;
    	}
    	public void setName(String name) { 
    		this.name = name;
    	}
    	public void setSex(String sex) { 
    		this.sex = sex;
    	}
    	public void setAge(Integer age) { 
    		this.age = age;
    	}
    	@Override
    	public String toString() { 
    		return "Student [name=" + name + ", sex=" + sex + ", age=" + age + "]";
    	}
    }

首先用fastjson进行测试：

*  当字段少于实体类字段：正常通过，没有的字段会被赋予默认值

//fastjson 少字段
    	@Test
    	public void testFastjson01() { 
    		String jsonStr = "{\"age\":18,\"name\":\"zhangsan\"}";
    		Student stu = JSON.parseObject(jsonStr, Student.class);
    		System.out.println(stu); // Student [name=zhangsan, sex=null, age=18]
    	}

*  当字段多于实体类字段：正常通过，没有的字段不会被反序列化到对象中

//fastjson 多字段
    	@Test
    	public void testFastjson02() { 
    		String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\",\"hobby\":\"basketball\"}";
    		Student stu = JSON.parseObject(jsonStr, Student.class);
    		System.out.println(stu); // Student [name=lisi, sex=男, age=20]
    	}

再用jackson进行测试：

*  当字段少于实体类字段：正常通过，没有的字段会被赋予默认值

//jackson 少字段
    	@Test
    	public void testJackson01() throws Exception{ 
    		String jsonStr = "{\"age\":18,\"name\":\"zhangsan\"}";
    		ObjectMapper om = new ObjectMapper();
    		Student stu = om.readValue(jsonStr, Student.class);
    		System.out.println(stu); // Student [name=zhangsan, sex=null, age=18]
    	}

*  当字段多于实体类字段：

//jackson 多字段
    	@Test
    	public void testJackson02() throws Exception{ 
    		String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\",\"hobby\":\"basketball\"}";
    		ObjectMapper om = new ObjectMapper();
    		Student stu = om.readValue(jsonStr, Student.class);
    		System.out.println(stu);
    	}

此时会报错，这个错翻译过来就是，一个无法识别的field。

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "hobby" (class com.cyj.demo03.Student), not marked as ignorable (3 known properties: "name", "sex", "age"])
     at [Source: {"age":20,"name":"lisi","sex":"男","hobby":"basketball"}; line: 1, column: 44] (through reference chain: com.cyj.demo03.Student["hobby"])
    	at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:51)
    	at com.fasterxml.jackson.databind.DeserializationContext.reportUnknownProperty(DeserializationContext.java:817)
    	at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:958)
    	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1324)
    	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1302)
    	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:249)
    	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
    	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3564)
    	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2580)
    	at com.cyj.demo03.TestJson.testJackson02(TestJson.java:40)
    	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    	at java.lang.reflect.Method.invoke(Method.java:497)
    	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
    	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
    	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
    	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)

由此可见，在默认情况下，jackson是不支持json串的字段多于实体类字段的，但是，jackson也提供了解决方案，我们在实体类上，添加注解@JsonIgnoreProperties，这个注解有一个ignoreUnknown属性，默认值为false，我们可以将它改为true,这样jackson在反序列化的时候，就会忽略掉不存在的属性了。（@JsonIgnoreProperties(ignoreUnknown = true)）  
![在这里插入图片描述][20181226211737150.png]

[20181226211737150.png]: /images/20220402/51ba260167804daa9e11186cb8aa2582.png