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。

 

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.bijian.study;

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();
    }
}

package com.bijian.study;

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();
    }
}

        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.bijian.study;

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

/**
 * The class JacksonUtil
 * 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
 *
 * json字符与对像转换
 */
public final class JacksonUtil {

    public static ObjectMapper objectMapper;

    /**
     * json对象转JAVA对象
     * 
     * @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.bijian.study;

import java.util.ArrayList;
import java.util.List;

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

/**
 * 实例实现利用jackson实现实体对象与json字符串的互相转换
 */
public class JacksonDemo {
    
    public static void main(String[] args) {

        UserBean userBean1 = new UserBean(1, "liubei", "123", "[e-mail]");
        UserBean userBean2 = new UserBean(2, "guanyu", "123", "[e-mail]");
        UserBean userBean3 = new UserBean(3, "zhangfei", "123", "[e-mail]");

        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);
    }
}

        运行结果：

deptBean to json:{"deptId":1,"deptName":"sanguo","userBeanList":[{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]"},{"userId":2,"userName":"guanyu","password":"123","email":"[e-mail]"},{"userId":3,"userName":"zhangfei","password":"123","email":"[e-mail]"}]}
userBean to json:{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]"}
json to DeptBean:DeptBean [deptId=1, deptName=sanguo, 
userBeanListString=UserBean [userId=1, userName=liubei, password=123, email=[e-mail]]
UserBean [userId=2, userName=guanyu, password=123, email=[e-mail]]
UserBean [userId=3, userName=zhangfei, password=123, email=[e-mail]]
]
json to UserBean:UserBean [userId=1, userName=liubei, password=123, email=[e-mail]]
list to json:[{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]"},{"userId":2,"userName":"guanyu","password":"123","email":"[e-mail]"},{"userId":3,"userName":"zhangfei","password":"123","email":"[e-mail]"}]
json to userBeans:UserBean [userId=1, userName=liubei, password=123, email=[e-mail]]
UserBean [userId=2, userName=guanyu, password=123, email=[e-mail]]
UserBean [userId=3, userName=zhangfei, password=123, email=[e-mail]]

 

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，并加上@JsonSerialize(using = JsonDateFormatFull.class)注解

package com.bijian.study;

import java.util.Date;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

public class UserBean {
    
    private int userId;
    
    private String userName;
    
    private String password;
    
    private String email;
    
    @JsonSerialize(using = JsonDateFormatFull.class)
    private Date createDate;

    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;
    }

    public Date getCreateDate() {
        return createDate;
    }

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

    @Override
    public String toString() {
        return "UserBean [userId=" + userId + ", userName=" + userName + ", password=" + password + ", email=" + email + ", createDate=" + createDate
                + "]";
    }

    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();
    }
}

package com.bijian.study;

import java.util.Date;
import java.util.List;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

public class DeptBean {
    
    private int deptId;
    
    private String deptName;
    
    @JsonSerialize(using = JsonDateFormatFull.class)
    private Date createDate;
    
    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 Date getCreateDate() {
        return createDate;
    }

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

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

    public DeptBean(int deptId, String deptName, List<UserBean> userBeanList) {
        super();
        this.deptId = deptId;
        this.deptName = deptName;
        this.userBeanList = userBeanList;
    }

    public DeptBean() {
        super();
    }
}

 

2.实现集成于JsonSerializer<Date>对象的工具类

package com.bijian.study;

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
 */
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.jackson日期互转具体实现

package com.bijian.study;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

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

/**
 * 利用jackson实现Json与实体对象的互转
 */
public class JacksonDemo {
    
    public static void main(String[] args) {

        UserBean userBean1 = new UserBean(1, "liubei", "123", "[e-mail]");
        userBean1.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));
        UserBean userBean2 = new UserBean(2, "guanyu", "123", "[e-mail]");
        userBean2.setCreateDate(new Date(Calendar.getInstance().getTimeInMillis()));
        UserBean userBean3 = new UserBean(3, "zhangfei", "123", "[e-mail]");
        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()));
        //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);
    }
}

        运行结果：

deptBean to json:{"deptId":1,"deptName":"sanguo","createDate":"2016-07-11T23:53:46","userBeanList":[{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"},{"userId":2,"userName":"guanyu","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"},{"userId":3,"userName":"zhangfei","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"}]}
userBean to json:{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"}
json to DeptBean:DeptBean [deptId=1, deptName=sanguo, createDate=Tue Jul 12 07:53:46 CST 2016, 
userBeanListString=UserBean [userId=1, userName=liubei, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
UserBean [userId=2, userName=guanyu, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
UserBean [userId=3, userName=zhangfei, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
]
json to UserBean:UserBean [userId=1, userName=liubei, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
list to json:[{"userId":1,"userName":"liubei","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"},{"userId":2,"userName":"guanyu","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"},{"userId":3,"userName":"zhangfei","password":"123","email":"[e-mail]","createDate":"2016-07-11T23:53:46"}]
json to userBeans:UserBean [userId=1, userName=liubei, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
UserBean [userId=2, userName=guanyu, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]
UserBean [userId=3, userName=zhangfei, password=123, email=[e-mail], createDate=Tue Jul 12 07:53:46 CST 2016]

 

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