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

<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

<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>

<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;

<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

<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

<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：

<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

<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

<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

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

4.jackson日期互转具体实现

<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

<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>

<span style="color: rgb(37, 37, 37); font-family: arial, 'microsoft yahei', 宋体, sans-serif; font-size: 14px; line-height: 26px;">以上为本博文的所有内容。</span><p style="margin-top: 0px; margin-bottom: 8px; padding-top: 0px; padding-bottom: 0px; color: rgb(37, 37, 37); font-family: arial, 'microsoft yahei', 宋体, sans-serif; font-size: 14px; line-height: 26px;"></p><p style="margin-top: 0px; margin-bottom: 8px; padding-top: 0px; padding-bottom: 0px; color: rgb(37, 37, 37); font-family: arial, 'microsoft yahei', 宋体, sans-serif; font-size: 14px; line-height: 26px;">源码下载地址：http://download.csdn.net/detail/a123demi/8394327</p>