Jackson实现Object对象与Json字符串的互转

在项目开发过程中，当客户端与服务器响应时，数据交互是必不可少的。然而通过Json实现数据交互成为我们开发中的一部分，进而Jackson为我们的Json转化提供了很好的机制。下面我将利用实例总结如何使用jackson.

一、准备

如果你需要使用jackson，你必须得导入相应的架包，有如下三个包

jackson-annotations；jackson-core；jackson-databind

Maven引入依赖代码

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<span style="font-size:18px;"> <dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-databind</artifactId>

<version>2.0.6</version>

</dependency>

<dependency>

<groupId>com.fasterxml.jackson.module</groupId>

<artifactId>jackson-module-jaxb-annotations</artifactId>

<version>2.0.6</version>

</dependency>

<dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-core</artifactId>

<version>2.3.0</version>

</dependency>

<dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-annotations</artifactId>

<version>2.3.0</version>

</dependency></span>

二、不带日期的对象实体与json互转

1.定义实体UserBean.java,DeptBean.java

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<span style="font-size:18px;">package com.jackson.bean;

import java.util.List;

public class DeptBean {

private int deptId;

private String deptName;

private List<UserBean> userBeanList;

public int getDeptId() {

return deptId;

}

public void setDeptId(int deptId) {

this.deptId = deptId;

}

public String getDeptName() {

return deptName;

}

public void setDeptName(String deptName) {

this.deptName = deptName;

}

public List<UserBean> getUserBeanList() {

return userBeanList;

}

public void setUserBeanList(List<UserBean> userBeanList) {

this.userBeanList = userBeanList;

}

@Override

public String toString() {

String userBeanListString = "";

for (UserBean userBean : userBeanList) {

userBeanListString += userBean.toString() + "\n";

}

return "DeptBean [deptId=" + deptId + ", deptName=" + deptName

+ ", \nuserBeanListString=" + userBeanListString + "]";

}

public DeptBean(int deptId, String deptName, List<UserBean> userBeanList) {

super();

this.deptId = deptId;

this.deptName = deptName;

this.userBeanList = userBeanList;

}

public DeptBean() {

super();

}

}

</span>

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<span style="font-size:18px;">package com.jackson.bean;

public class UserBean {

private int userId;

private String userName;

private String password;

private String email;

public int getUserId() {

return userId;

}

public void setUserId(int userId) {

this.userId = userId;

}

public String getUserName() {

return userName;

}

public void setUserName(String userName) {

this.userName = userName;

}

public String getPassword() {

return password;

}

public void setPassword(String password) {

this.password = password;

}

public String getEmail() {

return email;

}

public void setEmail(String email) {

this.email = email;

}

@Override

public String toString() {

return "UserBean [userId=" + userId + ", userName=" + userName

+ ", password=" + password + ", email=" + email + "]";

}

public UserBean(int userId, String userName, String password, String email) {

super();

this.userId = userId;

this.userName = userName;

this.password = password;

this.email = email;

}

public UserBean() {

super();

}

}

</span>

注意：在实体中必须存在无参的构造方法，否则转换时会有如下异常;

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<span style="font-size:18px;">com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class com.jackson.bean.UserBean]: can not instantiate from JSON object (need to add/enable type information?)</span>

2.jackson数据转换工具类

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<span style="font-size:18px;">package com.jackson.utils;

import com.fasterxml.jackson.core.type.TypeReference;

import com.fasterxml.jackson.databind.ObjectMapper;

/**

* The class JacksonUtil

*

* json字符与对像转换

*

* @version: $Revision$ $Date$ $LastChangedBy$

*

*/

public final class JacksonUtil {

public static ObjectMapper objectMapper;

/**

* 使用泛型方法，把json字符串转换为相应的JavaBean对象。

* (1)转换为普通JavaBean：readValue(json,Student.class)

* (2)转换为List,如List<Student>,将第二个参数传递为Student

* [].class.然后使用Arrays.asList();方法把得到的数组转换为特定类型的List

*

* @param jsonStr

* @param valueType

* @return

*/

public static <T> T readValue(String jsonStr, Class<T> valueType) {

if (objectMapper == null) {

objectMapper = new ObjectMapper();

}

try {

return objectMapper.readValue(jsonStr, valueType);

} catch (Exception e) {

e.printStackTrace();

}

return null;

}

/**

* json数组转List

* @param jsonStr

* @param valueTypeRef

* @return

*/

public static <T> T readValue(String jsonStr, TypeReference<T> valueTypeRef){

if (objectMapper == null) {

objectMapper = new ObjectMapper();

}

try {

return objectMapper.readValue(jsonStr, valueTypeRef);

} catch (Exception e) {

e.printStackTrace();

}

return null;

}

/**

* 把JavaBean转换为json字符串

*

* @param object

* @return

*/

public static String toJSon(Object object) {

if (objectMapper == null) {

objectMapper = new ObjectMapper();

}

try {

return objectMapper.writeValueAsString(object);

} catch (Exception e) {

e.printStackTrace();

}

return null;

}

}</span>

3.jackson数据转换具体实现

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<span style="font-size:18px;">package com.jackson.main;

import java.util.ArrayList;

import java.util.List;

import com.fasterxml.jackson.core.type.TypeReference;

import com.jackson.bean.DeptBean;

import com.jackson.bean.UserBean;

import com.jackson.utils.JacksonUtil;

/**

* 实例实现利用jackson实现实体对象与json字符串的互相转换

* @author liangming.deng

*

*/

public class JacksonDemo {

public static void main(String[] args){

UserBean userBean1 = new UserBean(1, "liubei", "123", "liubei@163.com");

UserBean userBean2 = new UserBean(2, "guanyu", "123", "guanyu@163.com");

UserBean userBean3 = new UserBean(3, "zhangfei", "123", "zhangfei@163.com");

List<UserBean> userBeans = new ArrayList<>();

userBeans.add(userBean1);

userBeans.add(userBean2);

userBeans.add(userBean3);

DeptBean deptBean = new DeptBean(1, "sanguo", userBeans);

//对象转json

String userBeanToJson = JacksonUtil.toJSon(userBean1);

String deptBeanToJson = JacksonUtil.toJSon(deptBean);

System.out.println("deptBean to json:" + deptBeanToJson);

System.out.println("userBean to json:" + userBeanToJson);

//json转字符串

UserBean jsonToUserBean = JacksonUtil.readValue(userBeanToJson, UserBean.class);

DeptBean jsonToDeptBean = JacksonUtil.readValue(deptBeanToJson, DeptBean.class);

System.out.println("json to DeptBean" + jsonToDeptBean.toString());

System.out.println("json to UserBean" + jsonToUserBean.toString());

//List 转json字符串

String listToJson = JacksonUtil.toJSon(userBeans);

System.out.println("list to json:" + listToJson);

//数组json转 List

List<UserBean> jsonToUserBeans = JacksonUtil.readValue(listToJson, new TypeReference<List<UserBean>>() {

});

String userBeanString = "";

for (UserBean userBean : jsonToUserBeans) {

userBeanString += userBean.toString() + "\n";

}

System.out.println("json to userBeans:" + userBeanString);

}

}

</span>

输出结果：

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<span style="font-size:18px;">deptBean to json:{"deptId":1,"deptName":"sanguo","userBeanList":[{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com"},{"userId":2,"userName":"guanyu","password":"123","email":"guanyu@163.com"},{"userId":3,"userName":"zhangfei","password":"123","email":"zhangfei@163.com"}]}

userBean to json:{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com"}

json to DeptBeanDeptBean [deptId=1, deptName=sanguo,

userBeanListString=UserBean [userId=1, userName=liubei, password=123, email=liubei@163.com]

UserBean [userId=2, userName=guanyu, password=123, email=guanyu@163.com]

UserBean [userId=3, userName=zhangfei, password=123, email=zhangfei@163.com]

]

json to UserBeanUserBean [userId=1, userName=liubei, password=123, email=liubei@163.com]

list to json:[{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com"},{"userId":2,"userName":"guanyu","password":"123","email":"guanyu@163.com"},{"userId":3,"userName":"zhangfei","password":"123","email":"zhangfei@163.com"}]

json to userBeans:UserBean [userId=1, userName=liubei, password=123, email=liubei@163.com]

UserBean [userId=2, userName=guanyu, password=123, email=guanyu@163.com]

UserBean [userId=3, userName=zhangfei, password=123, email=zhangfei@163.com]

</span>

三、带日期的实体对象与json转换

jackson实现带日期的实体对象与json转换有两种方法

1).将实体对象中的日期对象定义为String型，在使用的时候再将String型转换为Date型使用，其他就无需修改。

2).当实体对象中的日期对象定义为Date型，就需要通过集成JsonSerializer<Date>对象完成日期的转换，本段将重点讲解

1.在UserBean.java和DeptBean.java中分别添加Date createDate

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<span style="font-size:18px;"> private Date createDate;

public Date getCreateDate() {

return createDate;

}

public void setCreateDate(Date createDate) {

this.createDate = createDate;

}</span>

2.实现集成于JsonSerializer<Date>对象的工具类

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<span style="font-size:18px;">package com.jackson.utils;

import java.io.IOException;

import java.text.SimpleDateFormat;

import java.util.Date;

import com.fasterxml.jackson.core.JsonGenerator;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.databind.JsonSerializer;

import com.fasterxml.jackson.databind.SerializerProvider;

/**

* jackson日期转换工具类

*

* @author liangming.deng

*

*/

public class JsonDateFormatFull extends JsonSerializer<Date> {

/**

* Jackson支持日期字符串格式

* "yyyy-MM-dd'T'HH:mm:ss.SSSZ" "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"

* "EEE, dd MMM yyyy HH:mm:ss zzz" "yyyy-MM-dd"

*/

@Override

public void serialize(Date value, JsonGenerator jgen,

SerializerProvider provider) throws

IOException, JsonProcessingException {

SimpleDateFormat formatter = new SimpleDateFormat(

"yyyy-MM-dd'T'HH:mm:ss");

String formattedDate = formatter.format(value);

jgen.writeString(formattedDate);

}

}

</span>

3.在UserBean.java和DeptBean.java中Date变量加入如下注解

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<span style="font-size:18px;"> @JsonSerialize(using = JsonDateFormateFull.class)

private Date createDate;</span>

4.jackson日期互转具体实现

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<span style="font-size:18px;">package com.jackson.main;

import java.util.Date;

import java.util.ArrayList;

import java.util.Calendar;

import java.util.List;

import com.fasterxml.jackson.core.type.TypeReference;

import com.jackson.bean.DeptBean;

import com.jackson.bean.UserBean;

import com.jackson.utils.JacksonUtil;

/**

*利用jackson实现Json与实体对象的互转

* @author liangming.deng

*

*/

public class JacksonDemo {

public static void main(String[] args){

UserBean userBean1 = new UserBean(1, "liubei", "123", "liubei@163.com");

userBean1.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));

UserBean userBean2 = new UserBean(2, "guanyu", "123", "guanyu@163.com");

userBean2.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));

UserBean userBean3 = new UserBean(3, "zhangfei", "123", "zhangfei@163.com");

userBean3.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));

List<UserBean> userBeans = new ArrayList<>();

userBeans.add(userBean1);

userBeans.add(userBean2);

userBeans.add(userBean3);

DeptBean deptBean = new DeptBean(1, "sanguo", userBeans);

deptBean.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));

//实体对象 转json

String userBeanToJson = JacksonUtil.toJSon(userBean1);

String deptBeanToJson = JacksonUtil.toJSon(deptBean);

System.out.println("deptBean to json:" + deptBeanToJson);

System.out.println("userBean to json:" + userBeanToJson);

//json 转实体对象

UserBean jsonToUserBean = JacksonUtil.readValue(userBeanToJson, UserBean.class);

DeptBean jsonToDeptBean = JacksonUtil.readValue(deptBeanToJson, DeptBean.class);

System.out.println("json to DeptBean" + jsonToDeptBean.toString());

System.out.println("json to UserBean" + jsonToUserBean.toString());

//List 转json

String listToJson = JacksonUtil.toJSon(userBeans);

System.out.println("list to json:" + listToJson);

//json 转 List

List<UserBean> jsonToUserBeans = JacksonUtil.readValue(listToJson, new TypeReference<List<UserBean>>() {

});

String userBeanString = "";

for (UserBean userBean : jsonToUserBeans) {

userBeanString += userBean.toString() + "\n";

}

System.out.println("json to userBeans:" + userBeanString);

}

}

</span>

5.结果输出

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<span style="font-size:18px;">deptBean to json:{"deptId":1,"deptName":"sanguo","createDate":"2014-11-20T10:58:08","userBeanList":[{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com","createDate":"2014-11-20T10:58:08"},{"userId":2,"userName":"guanyu","password":"123","email":"guanyu@163.com","createDate":"2014-11-20T10:58:08"},{"userId":3,"userName":"zhangfei","password":"123","email":"zhangfei@163.com","createDate":"2014-11-20T10:58:08"}]}

userBean to json:{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com","createDate":"2014-11-20T10:58:08"}

json to DeptBeanDeptBean [deptId=1, deptName=sanguo,

userBeanListString=UserBean [userId=1, userName=liubei, password=123, email=liubei@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

UserBean [userId=2, userName=guanyu, password=123, email=guanyu@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

UserBean [userId=3, userName=zhangfei, password=123, email=zhangfei@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

]

json to UserBeanUserBean [userId=1, userName=liubei, password=123, email=liubei@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

list to json:[{"userId":1,"userName":"liubei","password":"123","email":"liubei@163.com","createDate":"2014-11-20T10:58:08"},{"userId":2,"userName":"guanyu","password":"123","email":"guanyu@163.com","createDate":"2014-11-20T10:58:08"},{"userId":3,"userName":"zhangfei","password":"123","email":"zhangfei@163.com","createDate":"2014-11-20T10:58:08"}]

json to userBeans:UserBean [userId=1, userName=liubei, password=123, email=liubei@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

UserBean [userId=2, userName=guanyu, password=123, email=guanyu@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

UserBean [userId=3, userName=zhangfei, password=123, email=zhangfei@163.com, createDate=Thu Nov 20 18:58:08 CST 2014]

</span>

以上为本博文的所有内容。

源码下载地址：http://download.csdn.net/detail/a123demi/8394327