SpringBoot 使用jackjson入门

SpringBoot中如果需要实现json的序列化和反序列化，我们会使用json解析工具。一般用到的有fastjson、GSON、Jackson
根据网上的测试，Jackson性能好一些，而且Jackson是SpringBoot默认引用的
本文记录SpringBoot如何使用Jackson

准备

1、在项目中创建包Jackson
2、分别创建4各类文件
2.1、Company实体类（里面包含Department的list）
2.2、Department实体类
2.3、jsonController controller类，接收测试请求
2.4、JsonHelper Jackson操作类
如题所示

每个类内容如下
Company

import java.util.ArrayList;import java.util.List;public class Company {    private  String name;    private  String address;    private  int employeesCount;    private List<Department> departmentArrayList;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address;    }    public int getEmployeesCount() {        return employeesCount;    }    public void setEmployeesCount(int employeesCount) {        this.employeesCount = employeesCount;    }    public List<Department> getDepartmentArrayList() {        return departmentArrayList;    }    public void setDepartmentArrayList(List<Department> departmentArrayList) {        this.departmentArrayList = departmentArrayList;    }}

Department

public class Department {    private  String name;    private  int employeesCount;    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getEmployeesCount() {        return employeesCount;    }    public void setEmployeesCount(int employeesCount) {        this.employeesCount = employeesCount;    }}

jsonController

import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.core.type.TypeReference;import com.fasterxml.jackson.databind.JavaType;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import java.util.*;@RestController@RequestMapping("/json")public class jsonController {    private  final Logger logger = LoggerFactory.getLogger(this.getClass());//对象方式初始化Log对象    @GetMapping("")    public String index() throws Exception {        JsonHelper jm = new JsonHelper();        //1、对象<->Json            //准备数据        Company c = getCompany();            //对象转Json        String json =  jm.toJson(c);        logger.info("1.1、对象转Json="+json);            //Json转对象        Company obj = jm.fromJson(json,Company.class);        logger.info("1.2、Json转对象="+ obj.getDepartmentArrayList().get(0).getName());        //2、Map<->Json            //Json转Map        Map map = jm.fromJson(json,Map.class);        List<Map> tempList =  (List<Map>)map.get("departmentArrayList");        logger.info("2.1、Json转Map="+tempList.get(0).get("name"));            //Map转Json        json =  jm.toJson(map);        logger.info("2.2、Map转Json="+json);        //3、List<Object> <->Json            //准备数据        List<Company> companyList = new ArrayList<Company>();        companyList.add(getCompany());        companyList.add(getCompany());        companyList.add(getCompany());            //List<Object>转Json        json =  jm.toJson(companyList);        logger.info("3.1、List<Object>转Json="+json);            //Json转List<Object>        List<Company> companyListDecode = jm.fromJson(json,new TypeReference<List<Company>>() {});        logger.info("3.2、Json转List<Object>="+companyListDecode.get(0).getDepartmentArrayList().get(0).getName());        //4、Map<String, Object><-> Json            //准备数据        Map<String, Company> map1 = new HashMap<String, Company>() ;        map1.put("1",getCompany());        map1.put("2",getCompany());        map1.put("3",getCompany());            //Map<String, Object>转Json        json =  jm.toJson(map1);        logger.info("4.1、Map<String, Object>转Json="+json);            //Json转Map<String, Object>        Map<String, Company> map1Decode = jm.fromJson(json,new TypeReference<Map<String, Company>>() {});        logger.info("4.2、Json转Map<String, Object>="+map1Decode.get("1").getDepartmentArrayList().get(0).getName());        //5、List<Map<String, Object>><->Json            //准备数据        List<Map<String, Company>> listMap =new ArrayList<Map<String, Company>>();        Map<String, Company> map2 = new HashMap<String, Company>() ;        map2.put("a",getCompany());        map2.put("b",getCompany());        map2.put("c",getCompany());        listMap.add(map1);        listMap.add(map2);            //List<Map<String, Object>> 转Json        json =  jm.toJson(listMap);        logger.info("5.1、List<Map<String, Object>> 转Json="+json);            //Json 转 List<Map<String, Object>>        List<Map<String, Company>> listMapDecode = jm.fromJson(json,new TypeReference<List<Map<String, Company>>>() {});        logger.info("5.2、List<Map<String, Object>> 转Json="+listMapDecode.get(0).get("1").getDepartmentArrayList().get(0).getName());        return "";    }    private  Company getCompany()    {        long time = new Date().getTime();        String sTime =  String.valueOf(time);        Company c = new Company();        c.setEmployeesCount(10);        c.setName("公司名"+sTime);        List list = new ArrayList();        Department d1= new Department();        d1.setEmployeesCount(5);        d1.setName("部门1"+sTime);        Department d2= new Department();        d2.setEmployeesCount(5);        d2.setName("部门2"+sTime);        list.add(d1);        list.add(d2);        c.setDepartmentArrayList(list);        return  c;    }}

JsonHelper

import com.fasterxml.jackson.annotation.JsonInclude;import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.core.type.TypeReference;import com.fasterxml.jackson.databind.DeserializationFeature;import com.fasterxml.jackson.databind.JavaType;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.SerializationFeature;import com.fasterxml.jackson.databind.util.JSONPObject;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import java.io.IOException;public class JsonHelper {    private  Logger logger = LoggerFactory.getLogger(this.getClass());    ObjectMapper mapper;    public  JsonHelper()    {        mapper = new ObjectMapper();        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);    }    public  JsonHelper(JsonInclude.Include include)    {        mapper = new ObjectMapper();        mapper.setSerializationInclusion(include);        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);    }    public  String toJson(Object object) throws JsonProcessingException {        return mapper.writeValueAsString(object);    }    public  <T> T fromJson(String json, Class<T> cls) throws IOException {        return mapper.readValue(json, cls);    }    public  <T> T fromJson(String json,TypeReference valueTypeRef) throws IOException {        return mapper.readValue(json, valueTypeRef);    }}

转换方式

共举例如下几种转换方式（整体在jsonController文件中，这里分别拆出来说明）

对象<->Json

//1、对象<->Json        //准备数据        Company c = getCompany();        //对象转Json        String json =  jm.toJson(c);        logger.info("1.1、对象转Json="+json);        //Json转对象        Company obj = jm.fromJson(json,Company.class);        logger.info("1.2、Json转对象="+ obj.getDepartmentArrayList().get(0).getName());

Map<->Json

//2、Map<->Json            //Json转Map        Map map = jm.fromJson(json,Map.class);        List<Map> tempList =  (List<Map>)map.get("departmentArrayList");        logger.info("2.1、Json转Map="+tempList.get(0).get("name"));            //Map转Json        json =  jm.toJson(map);        logger.info("2.2、Map转Json="+json);

List<Object> <->Json

//3、List<Object> <->Json            //准备数据        List<Company> companyList = new ArrayList<Company>();        companyList.add(getCompany());        companyList.add(getCompany());        companyList.add(getCompany());            //List<Object>转Json        json =  jm.toJson(companyList);        logger.info("3.1、List<Object>转Json="+json);            //Json转List<Object>        List<Company> companyListDecode = jm.fromJson(json,new TypeReference<List<Company>>() {});        logger.info("3.2、Json转List<Object>="+companyListDecode.get(0).getDepartmentArrayList().get(0).getName());

Map<String, Object><-> Json

//4、Map<String, Object><-> Json            //准备数据        Map<String, Company> map1 = new HashMap<String, Company>() ;        map1.put("1",getCompany());        map1.put("2",getCompany());        map1.put("3",getCompany());            //Map<String, Object>转Json        json =  jm.toJson(map1);        logger.info("4.1、Map<String, Object>转Json="+json);            //Json转Map<String, Object>        Map<String, Company> map1Decode = jm.fromJson(json,new TypeReference<Map<String, Company>>() {});        logger.info("4.2、Json转Map<String, Object>="+map1Decode.get("1").getDepartmentArrayList().get(0).getName());

List<Map<String, Object>><->Json

//5、List<Map<String, Object>><->Json            //准备数据        List<Map<String, Company>> listMap =new ArrayList<Map<String, Company>>();        Map<String, Company> map2 = new HashMap<String, Company>() ;        map2.put("a",getCompany());        map2.put("b",getCompany());        map2.put("c",getCompany());        listMap.add(map1);        listMap.add(map2);            //List<Map<String, Object>> 转Json        json =  jm.toJson(listMap);        logger.info("5.1、List<Map<String, Object>> 转Json="+json);            //Json 转 List<Map<String, Object>>        List<Map<String, Company>> listMapDecode = jm.fromJson(json,new TypeReference<List<Map<String, Company>>>() {});        logger.info("5.2、List<Map<String, Object>> 转Json="+listMapDecode.get(0).get("1").getDepartmentArrayList().get(0).getName());

测试

访问controller的方法，查看日志可以看出来每种转换都可以成功转为json，也可以成功转为对象

其它特性

在有些时候，我们会希望进行一些特殊处理，例如json不

忽略字段

@JsonIgnore 进行JSON操作时忽略该属性。
对于实体类中，如果有某个字段不希望参与json序列化与反序列化，可以把属性标记为@JsonIgnore
例如Company这个类
如果我们给Name、Address、employeesCount三个属性赋值了，序列化出来的内容是

{    "name": "公司名1504688970821",     "address": "地址",     "employeesCount": 10}

如果employeesCount是一个内容计数的值，不希望参与序列化，我们可以标记它

    @JsonIgnore    private  int employeesCount;

这样再次序列化的结果就变为了

{    "name": "公司名1504689048950",     "address": "地址"}

处理时间类型

@JsonFormat(pattern = “yyyy年MM月dd日”) 时间格式化
我们在Company实体类增加一个Date类型的属性，并且赋值序列化

    private Date createDate;    public Date getCreateDate() {        return createDate;    }    public void setCreateDate(Date createDate) {        this.createDate = createDate;    }

赋值然后再序列化，得到的内容是

{    "name": "公司名1504689283756",     "address": "地址",     "createDate": 1504689283756}

可以看到时间是一个数字
我们标记这个属性，再次序列化

{    "name": "公司名1504689362487",     "address": "地址",     "createDate": "2017年09月06日"}

时间按照指定的格式显示了

更改字段序列化名

@JsonProperty(“newName”) 改字段名
默认情况下，字段名是什么，序列化出来的key值也就是什么，如果我们希望序列化出来的名字和字段名不一样，则需要使用这个标记
我们把Company的name标记为newName

    @JsonProperty("newName")    private  String name;

然后进行序列化

{    "address": "地址",     "createDate": "2017年09月06日",     "newName": "公司名1504689496978"}

可以看出来，结果出来的key就使用了自定义的名字