记录一下一些关于Jackson工具类的使用

Jackson工具类 -封装

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.*;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.HashMap;

//提供将java对象转化成json结构
public final class JsonUtil{
    private static final ObjectMapper objectMapper=new ObjectMapper();
    private static final JsonUtil INSTANCE=new JsonUtil(); 
    private JsonUtil(){}
    public static JsonUtil getInstance(){
        return INSTANCE;
    }
    static{
        SimpleDateFormat dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//设置日期输出格式
        objectMapper.setDateFormat(dateFormat);
        //设置将对象转换成JSON字符串时候:包含的属性不能为空或"";
        //Include.Include.ALWAYS 默认
        //Include.NON_DEFAULT 属性为默认值不序列化
        //Include.NON_EMPTY 属性为 空（""） 或者为NULL都不序列化
        //Include.NON_NULL 属性为NULL 不序列化
        //objectMapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);//序列化的时候序列化全部的属性
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);
        //反序列化的时候如果多了其他属性,不抛出异常
        objectMapper.enable(SerializationFeature.INDENT_OUTPUT);//转化成格式化的json
        objectMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
        //是否允许一个类型没有注解表明打算被序列化。默认true，抛出一个异常；否则序列化一个空对象，比如没有任何属性。
        objectMapper.disable(SerializationFeature.FLUSH_AFTER_WRITE_VALUE);
        //该特性决定是否在writeValue()方法之后就调用JsonGenerator.flush()方法。
        //当我们需要先压缩，然后再flush，则可能需要false。
    }

     /**
     * @ 将对象序列化
     * @ param obj
     * @ return byte[]
     * @ create by ostreamBaba on 上午12:35 18-9-18
     */

    public static <T> byte[] serialize(T obj){
        byte[] bytes;
        try{
            bytes=objectMapper.writeValueAsBytes(obj);
        }catch (JsonProcessingException e){
            throw new IllegalStateException(e.getMessage(),e);
        }
        return bytes;
    }

    /**
     * @ 反序列成对象
     * @ param data
     * @ param clazz
     * @ return T
     * @ create by ostreamBaba on 上午12:35 18-9-18
     */

    public static <T> T deserialize(byte[] data,Class<T> clazz){
        T obj;
        try{
            obj=objectMapper.readValue(data,clazz);
        } catch (IOException e) {
            throw new IllegalStateException(e.getMessage(),e);
        }
        return obj;
    }

    /**
     * @ 将json转化成对象
     * @ param json
     * @ param clazz
     * @ return T
     * @ create by ostreamBaba on 上午12:37 18-9-18
     */

    public static <T> T jsonToObject(String json,Class<?> clazz){
        T obj;
        JavaType javaType=objectMapper.getTypeFactory().constructType(clazz);
        try{
            obj=objectMapper.readValue(json,javaType);
        } catch (IOException e) {
           throw new IllegalStateException(e.getMessage(),e);
        }
        return obj;
    }

    /**
     * @ 将json转化成list
     * @ param json
     * @ param collectionClass
     * @ param elementClass
     * @ return T
     * @ create by ostreamBaba on 上午12:38 18-9-18
     */

    public static <T> T jsonToObjectList(String json,Class<?> collectionClass,Class<?>... elementClass){
        T obj;
        JavaType javaType=objectMapper.getTypeFactory().constructParametricType(collectionClass,elementClass);
        try{
            obj=objectMapper.readValue(json,javaType);
        }catch (IOException e){
            throw new IllegalStateException(e.getMessage(),e);
        }
        return obj;
    }

    /**
     * @ 将json转化成Map
     * @ param json
     * @ param keyClass
     * @ param valueClass
     * @ return T
     * @ create by ostreamBaba on 上午12:38 18-9-18
     */

    public static <T> T jsonToObjectHashMap(String json,Class<?> keyClass,Class<?> valueClass){
        T obj;
        JavaType javaType=objectMapper.getTypeFactory().constructParametricType(HashMap.class,keyClass,valueClass);
        try {
            obj=objectMapper.readValue(json,javaType);
        }catch (IOException e){
            throw new IllegalStateException(e.getMessage(),e);
        }
        return obj;
    }

    /**
     * @ 将对象转化成json
     * @ param obj
     * @ return java.lang.String
     * @ create by ostreamBaba on 上午12:39 18-9-18
     */

    public static String objectToJson(Object obj){
        String json;
        try{
            json=objectMapper.writeValueAsString(obj);
        }catch (IOException e){
            throw new IllegalStateException(e.getMessage(),e);
        }
        return json;
    }
}

• objectMappe属性设置可以参考一下这篇文章: Jackson 工具类使用及配置指南

关于上面工具类的一些测试

public class test {
    //测试json转化成list
    @Test
    public void test(){
        List<Bean> beanList=new ArrayList<>();
        beanList.add(new Bean(1));
        beanList.add(new Bean(2));
        beanList.add(new Bean(3));
        beanList.add(new Bean(4));
        String json=JsonUtil.objectToJson(beanList);
        System.out.println(JsonUtil.jsonToObjectList(json,List.class,Bean.class).getClass());
        List<Bean> list=JsonUtil.jsonToObjectList(json,List.class,Bean.class);
        list.forEach(v->System.out.println(v.getId()));
    }
	//测试json转化成map
    @Test
    public void testJsonToObjectMap(){
        Map<String,Object> map=new HashMap<>();
        map.put("name","ostreamBaba");
        map.put("age",20);
        map.put("sex",'f');
        String json=JsonUtil.objectToJson(map);
        System.out.println(json);
        Map<String,Object> t=JsonUtil.jsonToObjectHashMap(json,String.class,Object.class);
        t.forEach((k,v)-> System.out.println(k+" "+v));
    }
}
//测试类
public class Bean implements Serializable{
    private static final long serialVersionUID = 168070289504099944L;
    private int id;
    public Bean() {}
    public Bean(int id) {
        this.id = id;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
}