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>

以上为本博文的所有内容。

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