Jackson详细介绍

朱雀 2022-07-12 19:28 145阅读 0赞

Jackson是基于Java平台的一套数据处理工具，被称为”最好的Java Json解析器”。它可以使我们高效、简便的处理json字符串。

1、Jackson的版本以及maven依赖**重点内容**

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.7.4</version>
    </dependency>

**2、将java对象转换为json字符串**

public class Goods {
    
        //商品id
        private BigInteger goodsId;
    
    
        private String data;
    
        //商品是否可用标志，true可用，false不可用
        private String status;
    
        //数据插入或者更新时间
        private String ctime;
    
        //商品版本号
        private Long version;
    
        public BigInteger getGoodsId() {
            return goodsId;
        }
    
        public void setGoodsId(BigInteger goodsId) {
            this.goodsId = goodsId;
        }
    
        public String getData() {
            return data;
        }
    
        public void setData(String data) {
            this.data = data;
        }
    
        public String getStatus() {
            return status;
        }
    
        public void setStatus(String status) {
            this.status = status;
        }
    
        public String getCtime() {
            return ctime;
        }
    
        public void setCtime(String ctime) {
            this.ctime = ctime;
        }
    
        public Long getVersion() {
            return version;
        }
    
        public void setVersion(Long version) {
            this.version = version;
        }
    }

import com.fasterxml.jackson.annotation.JsonInclude;
    import com.fasterxml.jackson.core.type.TypeReference;
    import com.fasterxml.jackson.databind.DeserializationFeature;
    import com.fasterxml.jackson.databind.ObjectMapper;
    import com.fasterxml.jackson.databind.SerializationFeature;
    
    public class TestWriteJson1 {
    
         private ObjectMapper OBJECT_MAPPER = new ObjectMapper()
                .setSerializationInclusion(JsonInclude.Include.NON_EMPTY)  //类级别的设置，JsonInclude.Include.NON_EMPTY标识只有非NULL的值才会被纳入json string之中，其余的都将被忽略
                .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES) //禁止使用出现未知属性之时，抛出异常
    
    .disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)
                .setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);//转化后的json的key命名格式
    
        @Test
        public void writeJson() throws JsonProcessingException {
    
            Goods goods = new Goods();
            goods.setGoodsId("1234");
            goods.setData("data");
            goods.setCtime("2017-02-24");
    
            String jsonStr = OBJECT_MAPPER.writeValueAsString(goods);
    
            System.out.println("JSON:" + jsonStr);
        }
    }

**3、String对象转为json格式**

public class TestWriteJson2 {
    
         private ObjectMapper OBJECT_MAPPER = new ObjectMapper()
                .setSerializationInclusion(JsonInclude.Include.NON_EMPTY)//类级别的设置，JsonInclude.Include.NON_EMPTY标识只有非NULL的值才会被纳入json string之中，其余的都将被忽略
                .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)//禁止使用出现未知属性之时，抛出异常
    
    .disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)
                .setPropertyNamingStrategy(PropertyNamingStrategy.CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES);//转化后的json的key命名格式
    
        @Test
        public void writeJson() throws JsonProcessingException {
    
            //1、str对象的属性具有很强的统一性，属性固定
            String str = "";
    
            Goods goods = null;
            try {
                goods = new ObjectMapper().readValue(str, new TypeReference<Goods>() {
                });
            } catch (IOException e) {
    
            }
    
            if(goods != null){
                //取出相应属性
            }
    
    
            //2、str对象的属性没有很强的统一性，有可能属性缺失
            String str = "";
            // Jackson提供一个树节点被称为"JsonNode",ObjectMapper提供方法来读json作为树的JsonNode根节点
            JsonNode jsonNode = objectMapper.readTree(valueParser);
            List<JsonNode> dataList = jsonNode.findValues("data");
            if(dataList != null && dataList.size() > 0){
                //取出相应属性
    
                // 得到所有node节点的子节点名称
                Iterator<String> fieldNames = dataList.fieldNames();  
                while (fieldNames.hasNext()) { 
                    String fieldName = fieldNames.next();  
                    System.out.print(fieldName+" ");  
                }
    
    
                //得到某个属性值
                JsonNode goodId = dataList.get("goodId"); 
    
            }               
        }
    }