fastjson和jackson JSON转换实践

        在实际开发过程，需将请求第三方返回的JSON串转成JAVA对象，用fastjson发现，如果JAVA对象中缺少JSON串的key，将不能正常转换，将会报报Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "amount"之类的异常。当然可以补全JAVA对象中属性，但毕竟是第三方返回的JSON串，以后第三方如果再增加新的key那也必须同时修改我们的JAVA对象，就强依赖了。于是用jackson工具，发现无此问题。

        下面是测试验证的完整代码：

UserDTO.java

package com.bijian.test;

public class UserDTO {

    private String name;
    private int age;
    private String city;
    private String grade;
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public String getGrade() {
        return grade;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }
    
    @Override
    public String toString() {
        return "UserDTO [name=" + name + ", age=" + age + ", city=" + city + ", grade=" + grade + "]";
    }
}

JacksonUtil.java

package com.bijian.test;

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

/**
 * json字符与对像转换
 */
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
     * @throws Exception 
     */
    public static <T> T readValue(String jsonStr, Class<T> valueType) throws Exception {
        
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.readValue(jsonStr, valueType);
        } catch (Exception e) {
            throw e;
        }
    }

    /**
     * json数组转List
     * @param jsonStr
     * @param valueTypeRef
     * @return
     * @throws Exception 
     */
    public static <T> T readValue(String jsonStr, TypeReference<T> valueTypeRef) throws Exception {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.readValue(jsonStr, valueTypeRef);
        } catch (Exception e) {
            throw e;
        }
    }

    /**
     * 把JavaBean转换为json字符串
     * 
     * @param object
     * @return
     * @throws Exception 
     */
    public static String toJson(Object object) throws Exception {
        
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
        }

        try {
            return objectMapper.writeValueAsString(object);
        } catch (Exception e) {
            throw e;
        }
    }
    
    public static void main(String[] args) throws Exception {
        
        //报Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "amount"异常
        String str = "{\"name\":\"白白\",\"age\":18,\"city\":\"shengzhen\",\"amount\":100,\"total\":\"172cm\"}";
        
        //OK
        //String str = "{\"name\":\"白白\",\"age\":18,\"city\":\"shengzhen\"}";
        UserDTO userDTO = JacksonUtil.readValue(str, UserDTO.class);
        System.out.println(userDTO);
    }
}

FastJsonUtil.java

package com.bijian.test;

import java.util.Map;
import java.util.Map.Entry;

import com.alibaba.fastjson.JSON;

public class FastJsonUtil {

    /**
     * 把json字符串转换为map
     * 
     * @param jsonStr
     * @return
     */
    public static Map<String, Object> json2Map(String jsonStr) {

        Map<String, Object> resMap = (Map<String, Object>) JSON.parse(jsonStr);
        return resMap;
    }
    
    /**
     * 把json字符串转换为相应的JavaBean对象
     * 
     * @param jsonStr
     * @param valueType
     * @return
     */
    public static <T> T toObject(String jsonStr, Class<T> valueType) {
        
        return JSON.parseObject(jsonStr, valueType);
    }
    
    /**
    * 把JavaBean转换为json字符串
    * 
    * @param object
    * @return
    * @throws Exception 
    */
    public static String toJson(Object object) {

        return JSON.toJSONString(object);
    }
    
    public static void main(String[] args) throws Exception {
        
        String str = "{\"name\":\"白白\",\"age\":18,\"city\":\"shengzhen\",\"amount\":100,\"total\":\"172cm\"}";
        UserDTO userDTO = FastJsonUtil.toObject(str, UserDTO.class);
        System.out.println(userDTO);
        
        
        Map<String, Object> resMap = FastJsonUtil.json2Map(str);
        for(Entry<String, Object> entry : resMap.entrySet()) {
            System.out.println(entry.getKey() + ":" + entry.getValue());
        }
    }
}