背景

在前后端分離的項(xiàng)目中，后端經(jīng)常涉及到j(luò)son與對(duì)象互轉(zhuǎn)的場(chǎng)景。阿里巴巴的Fastjson是好用，但是，因?yàn)榧夹g(shù)領(lǐng)導(dǎo)的原因（可能因?yàn)閒astjson1的各種問(wèn)題很多吧），不讓用，所以就需要選擇其他技術(shù)棧。當(dāng)前比較常用的是SpringBoot自帶的Jackson或者谷歌的Gson。
下面，做一下使用Jackson的總結(jié)。

JavaBean準(zhǔn)備

Company，公司

@Data @NoArgsConstructor @AllArgsConstructor public class Company {private String companyName;private List<WebSite> webSites; }

WebSite，站點(diǎn)

@Data @NoArgsConstructor @AllArgsConstructor public class WebSite {private String webSiteName;private List<User> users;}

User，用戶

@Data @NoArgsConstructor @AllArgsConstructor public class User {private String userId;private String username;private String password; }

json字符串和對(duì)象互轉(zhuǎn)

對(duì)象轉(zhuǎn)json字符串

不管你是什么結(jié)構(gòu)的對(duì)象，想轉(zhuǎn)json，直接objectMapper.writeValueAsString()搞定。

/*** 序列化：對(duì)象轉(zhuǎn)json字符串，包含多個(gè)數(shù)組**/@Testpublic void testObject2Json2() {User user2 = new User("1","上海辟謠專屬隊(duì)","職業(yè)辟謠，不信謠，不傳謠，呵呵");List<User> users = new ArrayList<>();users.add(user2);WebSite webSite = new WebSite();webSite.setWebSiteName("xxxxxx.com");webSite.setUsers(users);List<WebSite> webSites = new ArrayList<>();webSites.add(webSite);Company company = new Company();company.setCompanyName("yyyyyy");company.setWebSites(webSites);ObjectMapper objectMapper = new ObjectMapper();try {String jsonString = objectMapper.writeValueAsString(company);System.out.println(jsonString);} catch (JsonProcessingException e) {log.error("error: ", e);}}

輸出：

{"companyName":"yyyyyy","webSites":[{"webSiteName":"xxxxxx.com","users":[{"userId":"1","username":"上海辟謠專屬隊(duì)","password":"職業(yè)辟謠，不信謠，不傳謠，呵呵"}]}]}

json字符串轉(zhuǎn)對(duì)象

注意：這種情形是json對(duì)象字符串，不能是json數(shù)組字符串，后面會(huì)說(shuō)到。

@Testpublic void testJson2Object() {String json = "{\"companyName\":\"yyyyyy\",\"webSites\":[" +"{\"webSiteName\":\"xxxxxx.com\",\"users\":[{\"userId\":\"1\",\"username\":\"上海辟謠專屬隊(duì)\",\"password\":\"職業(yè)辟謠，不信謠，不傳謠，呵呵\"}]}" +"]}";ObjectMapper objectMapper = new ObjectMapper();try {Company company = objectMapper.readValue(json, Company.class);System.out.println(company.getWebSites().get(0).getUsers().get(0).getUsername());} catch (JsonProcessingException e) {log.error("error: ", e);}}

輸出：

上海辟謠專屬隊(duì)

json數(shù)組字符串和數(shù)組（集合）對(duì)象互轉(zhuǎn)

有個(gè)大坑

數(shù)組對(duì)象轉(zhuǎn)json數(shù)組字符串

/*** 序列化：數(shù)組對(duì)象轉(zhuǎn)json數(shù)組類型的字符串**/@Testpublic void testObjectArray2JsonArrayString() {User user1 = new User("1","上海帶刀滬衛(wèi)","帶刀大佬");User user2 = new User("1","上海辟謠專屬隊(duì)","職業(yè)辟謠，不信謠，不傳謠，呵呵");List<User> users = new ArrayList<>();users.add(user1);users.add(user2);ObjectMapper objectMapper = new ObjectMapper();try {String json = objectMapper.writeValueAsString(users);System.out.println(json);} catch (JsonProcessingException e) {log.error("error: ", e);}}

輸出：

[{"userId":"1","username":"上海帶刀滬衛(wèi)","password":"帶刀大佬"},{"userId":"1","username":"上海辟謠專屬隊(duì)","password":"職業(yè)辟謠，不信謠，不傳謠，呵呵"}]

json數(shù)組字符串轉(zhuǎn)數(shù)組對(duì)象

先演示一下錯(cuò)誤的寫(xiě)法，先演示一下錯(cuò)誤的寫(xiě)法，先演示一下錯(cuò)誤的寫(xiě)法，重要的事情說(shuō)三遍！

/*** 反序列化：數(shù)組類型的json字符串轉(zhuǎn)對(duì)象數(shù)組**/@Testpublic void testJsonArrayString2ObjectArray() {String json = "[" +"{\"userId\":\"1\",\"username\":\"上海帶刀滬衛(wèi)\",\"password\":\"帶刀大佬\(zhòng)"}" +",{\"userId\":\"1\",\"username\":\"上海辟謠專屬隊(duì)\",\"password\":\"職業(yè)辟謠，不信謠，不傳謠，呵呵\"}" +"]";ObjectMapper objectMapper = new ObjectMapper();try {//錯(cuò)誤寫(xiě)法List<User> list = objectMapper.readValue(json, List.class);list.forEach(user -> {System.out.println(user.getUsername());});} catch (JsonProcessingException e) {log.error("error: ", e);}}

輸出異常：

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.xywei.springboot.springtestdemo.entity.Userat java.util.ArrayList.forEach(ArrayList.java:1259)at com.xywei.springboot.springtestdemo.junit.TestUseJackson.testJsonArrayString2ObjectArray(TestUseJackson.java:160)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:498)at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)at #省略大段…… Process finished with exit code -1

因?yàn)閷?shí)際轉(zhuǎn)成了map類型，所以使用List方式取值是錯(cuò)的！
正確做法：

/*** 反序列化：數(shù)組類型的json字符串轉(zhuǎn)對(duì)象數(shù)組**/@Testpublic void testJsonArrayString2ObjectArray() {String json = "[" +"{\"userId\":\"1\",\"username\":\"上海帶刀滬衛(wèi)\",\"password\":\"帶刀大佬\(zhòng)"}" +",{\"userId\":\"1\",\"username\":\"上海辟謠專屬隊(duì)\",\"password\":\"職業(yè)辟謠，不信謠，不傳謠，呵呵\"}" +"]";ObjectMapper objectMapper = new ObjectMapper();try {TypeReference<List<User>> typeReference = new TypeReference<List<User>>() {};List<User> list = objectMapper.readValue(json, typeReference);list.forEach(user -> {System.out.println(user.getUsername());});} catch (JsonProcessingException e) {log.error("error: ", e);}}

最終輸出：

上海帶刀滬衛(wèi) 上海辟謠專屬隊(duì)

同時(shí)，對(duì)多層嵌套的數(shù)組也適用：

@Testpublic void testJsonArrayString2ObjectArray2() {String json = "[" +"{" +"\"companyName\":\"yyyyyy\",\"webSites\":[" +"{\"webSiteName\":\"xxxxxx.com\",\"users\":[" +"{\"userId\":\"1\",\"username\":\"上海辟謠專屬隊(duì)\",\"password\":\"職業(yè)辟謠，不信謠，不傳謠，呵呵\"}" +"]" +"}" +"]" +"}" +"]";ObjectMapper objectMapper = new ObjectMapper();try {TypeReference<List<Company>> typeReference = new TypeReference<List<Company>>() {};List<Company> list = objectMapper.readValue(json, typeReference);list.forEach(company -> {System.out.println(company.getWebSites().get(0).getUsers().get(0).getUsername());});} catch (JsonProcessingException e) {log.error("error: ", e);}}

總結(jié)

以上是在項(xiàng)目中常用的，當(dāng)然還有一些小弟沒(méi)有用過(guò)的，希望各位大佬分享一下！

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