Jackson实现Object对象与Json字符串的互转

向右看齐 2022-09-25 12:23 187阅读 0赞

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

<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>

二、不带日期的对象实体与json互转

## 1.定义实体UserBean.java,DeptBean.java ##

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();
 	}
 	
 	
 }

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();
 	}
 	
 	
 }

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;

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?)

## 2.jackson数据转换工具类 ##

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;
 	}
 
 }

## 3.jackson数据转换具体实现 ##

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);
 	}
 	
 	
 }

输出结果：

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]

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 ##

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

## 2.实现集成于JsonSerializer<Date>对象的工具类 ##

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);
 
 	}
 
 }

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

@JsonSerialize(using = JsonDateFormateFull.class)
 	private Date createDate;

## 4.jackson日期互转具体实现 ##

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);
 	}
 	
 	
 }

## 5.结果输出 ##

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]