這里我們對(duì)json串和實(shí)體類字段不一致的情況進(jìn)行一個(gè)測試：
首先，我們建立一個(gè)實(shí)體類：這里簡單定義了name,sex,age三個(gè)屬性，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進(jìn)行測試：
當(dāng)字段少于實(shí)體類字段：正常通過，沒有的字段會(huì)被賦予默認(rèn)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]
- }
當(dāng)字段多于實(shí)體類字段：正常通過，沒有的字段不會(huì)被反序列化到對(duì)象中
- //fastjson 多字段
- @Test
- public void testFastjson02() {
- String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\(zhòng)",\"hobby\":\"basketball\"}";
- Student stu = JSON.parseObject(jsonStr, Student.class);
- System.out.println(stu); // Student [name=lisi, sex=男, age=20]
- }
再用jackson進(jìn)行測試：
當(dāng)字段少于實(shí)體類字段：正常通過，沒有的字段會(huì)被賦予默認(rèn)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]
- }
當(dāng)字段多于實(shí)體類字段：
- //jackson 多字段
- @Test
- public void testJackson02() throws Exception{
- String jsonStr = "{\"age\":20,\"name\":\"lisi\",\"sex\":\"男\(zhòng)",\"hobby\":\"basketball\"}";
- ObjectMapper om = new ObjectMapper();
- Student stu = om.readValue(jsonStr, Student.class);
- System.out.println(stu);
- }
此時(shí)會(huì)報(bào)錯(cuò)，這個(gè)錯(cuò)翻譯過來就是，一個(gè)無法識(shí)別的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)
由此可見，在默認(rèn)情況下，jackson是不支持json串的字段多于實(shí)體類字段的，但是，jackson也提供了解決方案，我們在實(shí)體類上，添加注解@JsonIgnoreProperties，這個(gè)注解有一個(gè)ignoreUnknown屬性，默認(rèn)值為false，我們可以將它改為true,這樣jackson在反序列化的時(shí)候，就會(huì)忽略掉不存在的屬性了。（@JsonIgnoreProperties(ignoreUnknown = true)）
補(bǔ)充：json字段名不一致的問題
1.場景
項(xiàng)目開發(fā)過程中，有時(shí)候可能要對(duì)接第三方平臺(tái)，可能就會(huì)存在字段名不一樣的問題，而雙方的字段名不一致， 而代碼開發(fā)已經(jīng)有一段時(shí)間勒，如果就因?yàn)樽侄蚊灰粯拥膯栴}，雙方改成屬性名一致，這樣改動(dòng)量太大，也不保險(xiǎn)，下面我來接手一下，針對(duì)這種場景，如果解決。
假設(shè)： 系統(tǒng)通過http對(duì)接，傳的是json。有一個(gè)參數(shù)"名稱"
第三方平臺(tái)：name
開發(fā)環(huán)境：userName
直接通過實(shí)體類映射，不用說肯定有問題
2.解決方法
- @JsonProperty("name")
- private String userName;
在實(shí)體類的屬性上增加一個(gè)注解就可以解決這種問題。
以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持我們。如有錯(cuò)誤或未考慮完全的地方，望不吝賜教。
原文鏈接：https://blog.csdn.net/MrHamster/article/details/85268990
