JSON解析之ObjectMapper使用

ObjectMapper的使用

这个类是jackson提供的，主要是用来把对象转换成为一个json字符串返回到前端,现在几乎所有数据交换都是以json来传输的。它使用JsonParser和JsonGenerator的实例实现JSON实际的读/写。当然这只是其中的一种 后续我还会将介绍比较火的Gson。

首先在pom.xml文件中，加入依赖：

            com.fasterxml.jackson.core
            jackson-databind
            2.8.3
        

代码解释

package com.ghl.demo;

import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

public class ObjectMapperDemo {
public static void main(String[] args) throws Exception {
	/*testObj();*/
	/*testList();*/
	testMap();
	}
	/**
	 * 1.对象转json格式的字符串
	 * 2.对象转字节数组
	 * 3.json字符串转为对象
	 * 4.byte数组转为对象 
	 * @throws Exception
	 */
	public static void testObj() throws Exception {
		//创建转换对象 使用默认的构造方法，使用的是JsonParsers和JsonGenerators映射
		ObjectMapper mapper=new ObjectMapper();
		// 转换为格式化的json
	    mapper.enable(SerializationFeature.INDENT_OUTPUT);
	    // 如果json中有新增的字段并且是实体类类中不存在的，不报错
	    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		//创建学生对象
	    Student stu=new Student("ghl", 12, "123", "[email protected]");
	    //1.对象转json格式的字符串
	    String stuToString = mapper.writeValueAsString(stu);
	    //System.out.println("对象转为字符串：" + stuToString);
	    /*
	     * 输出结果：
	     * 对象转为字符串：{
					  "name" : "ghl",
					  "age" : 12,
					  "password" : "123",
					  "email" : "[email protected]"
				}
	     */
	    
	    
	    //2.对象转字节数组
	    byte[] byteArr = mapper.writeValueAsBytes(stu);
        System.out.println("对象转为byte数组：" + byteArr);
	    /*
	     * 对象转为byte数组：[B@6aaa5eb0
	     */
        
        
      //3.json字符串转为对象
        Student student = mapper.readValue(stuToString, Student.class);
        System.out.println("json字符串转为对象：" + student);
	    //json字符串转为对象：Student [name=ghl, age=12, password=123, [email protected]]
      
        
        //4.byte数组转为对象 
    	Student student2 = mapper.readValue(byteArr, Student.class);
         System.out.println("byte数组转为对象：" + student2);
         //输出结果：byte数组转为对象：Student [name=ghl, age=12, password=123, [email protected]]
         
         
         mapper.writeValue(new File("D:/test.txt"), stu); // 写到文件中
	}
	
	/**list集合与json字符的转换
	 * 1.集合转为字符串
	 * 2.字符串转集合
	 * @throws Exception 
	 * 
	 */
	public static void testList() throws Exception {
	   //创建转换对象 使用默认的构造方法，使用的是JsonParsers和JsonGenerators映射
		ObjectMapper mapper=new ObjectMapper();
		// 转换为格式化的json
	    mapper.enable(SerializationFeature.INDENT_OUTPUT);
	    // 如果json中有新增的字段并且是实体类类中不存在的，不报错
	    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		List studnetList = new ArrayList();
		studnetList.add(new Student("zs", 12, "121", "[email protected]"));
		studnetList.add(new Student("lisi", 13, "122", "[email protected]"));
		studnetList.add(new Student("wangwu", 14, "123", "[email protected]"));
		studnetList.add(new Student("zhangliu", 15, "124", "[email protected]"));
		//1.集合转为字符串
		String jsonStr = mapper.writeValueAsString(studnetList);
	     System.out.println("集合转为字符串：" + jsonStr);
	     /*輸出結果
	      * 集合转为字符串：[ {
					  "name" : "zs",
					  "age" : 12,
					  "password" : "121",
					  "email" : "[email protected]"
					}, {
					  "name" : "lisi",
					  "age" : 13,
					  "password" : "122",
					  "email" : "[email protected]"
					}, {
					  "name" : "wangwu",
					  "age" : 14,
					  "password" : "123",
					  "email" : "[email protected]"
					}, {
					  "name" : "zhangliu",
					  "age" : 15,
					  "password" : "124",
					  "email" : "[email protected]"
					} ]
	      * 
	      */
	     
	     
	     //2.字符串转集合
	     List userListDes = mapper.readValue(jsonStr, List.class);
	     System.out.println("字符串转集合：" + userListDes);
	     /*輸出結果
	      * 字符串转集合：[{name=zs, age=12, password=121, [email protected]}, 
			      * {name=lisi, age=13, password=122, [email protected]}, 
			      * {name=wangwu, age=14, password=123, [email protected]}, 
			      * {name=zhangliu, age=15, password=124, [email protected]}]
	      */
	}
	
	/**Map与字符串转换
	 * 1.Map转为字符串
	 * 2.字符串转Map
	 * @throws Exception
	 */
	public static void testMap() throws Exception {
		   //创建转换对象 使用默认的构造方法，使用的是JsonParsers和JsonGenerators映射
			ObjectMapper mapper=new ObjectMapper();
			// 转换为格式化的json
		    mapper.enable(SerializationFeature.INDENT_OUTPUT);
		    // 如果json中有新增的字段并且是实体类类中不存在的，不报错
		    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
		    Map testMap = new HashMap();
	        testMap.put("name", "ghl");
	        testMap.put("age", 18);
	        //1.Map转为字符串
	        String jsonStr = mapper.writeValueAsString(testMap);
            System.out.println("Map转为字符串：" + jsonStr);
            /*
             * Map转为字符串：{
						  "name" : "ghl",
						  "age" : 18
						}
             */
            //2.字符串转Map
            Map testMapDes = mapper.readValue(jsonStr, Map.class);
            System.out.println("字符串转Map：" + testMapDes);
		    /*
		     	* 字符串转Map：{name=ghl, age=18}
		     */
	}
}

jsonUtils工具类

POM文件

			com.fasterxml.jackson.core
			jackson-databind
			2.8.3
		
		
		
			com.alibaba
			fastjson
			1.1.32
		

json工具类

package com.ghl.demo;

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

import com.alibaba.fastjson.JSON;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;


public class JsonUtils {

    // 定义jackson对象
    private static final ObjectMapper MAPPER = new ObjectMapper();

    /**
     * 将对象转换成json字符串�??
     * 
Title: pojoToJson
     * 
Description: 
     * @param data
     * @return
     */
    public static String objectToJson(Object data) {
    	try {
			String string = MAPPER.writeValueAsString(data);
			return string;
		} catch (JsonProcessingException e) {
			e.printStackTrace();
		}
    	return null;
    }
    
    /**
     * 将json结果集转化为对象
     * 
     * @param jsonData json数据
     * @param clazz 对象中的object类型
     * @return
     */
    public static  T jsonToPojo(String jsonData, Class beanType) {
        try {
            T t = MAPPER.readValue(jsonData, beanType);
            return t;
        } catch (Exception e) {
        	e.printStackTrace();
        }
        return null;
    }
    
    /**
     * 将json数据转换成pojo对象list
     * 
Title: jsonToList
     * 
Description: 
     * @param jsonData
     * @param beanType
     * @return
     */
    public static List jsonToList(String jsonData, Class beanType) {
    	JavaType javaType = MAPPER.getTypeFactory().constructParametricType(List.class, beanType);
    	try {
    		List list = MAPPER.readValue(jsonData, javaType);
    		return list;
		} catch (Exception e) {
			e.printStackTrace();
		}
    	
    	return null;
    }
    
    public static  T getJson(String jsonString, Class cls) {
    	T t = null;
    	try {
    	t = JSON.parseObject(jsonString, cls);
    	} catch (Exception e) {
    	// TODO: handle exception
    	e.printStackTrace();
    	}
    	return t;
    }

    public static  List getArrayJson(String jsonString, Class cls) {
    	List list = new ArrayList();
    	try {
    	list = JSON.parseArray(jsonString, cls);
    	} catch (Exception e) {
    	// TODO: handle exception
    	}
    	return list;
    }
    
    
    
}