使用Jackson处理JSON数据

Json 数据处理技术 之 Jackson Maven依赖

    com.fasterxml.jackson.core
    jackson-core
    2.9.7


    com.fasterxml.jackson.core
    jackson-databind
    2.9.7


    com.fasterxml.jackson.core
    jackson-annotations
    2.9.7

示例：实体类序列化和反序列化

public static void main(String[] args) throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();

    Dept dept = new Dept(10, "ACCOUNTING", "NEWYORK");

    //序列化
    String json = objectMapper.writeValueAsString(dept);
    System.out.println(json);

    //反序列化
    Dept res = objectMapper.readValue(json, Dept.class);
    System.out.println(res);

}

示例：List序列化和反序列化

public static void main(String[] args) throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();

    List depts = new ArrayList();
    depts.add(new Dept(10,"ACCOUNTING","NEWYORK"));
    depts.add(new Dept(20,"RESEARCH","DALLAS"));
    depts.add(new Dept(30,"SALES","CHICAGO"));
    depts.add(new Dept(40,"OPERATIONS","BOSTON"));

    //序列化
    String json = objectMapper.writeValueAsString(depts);
    System.out.println(json);

    //反序列化
    JavaType type = objectMapper.getTypeFactory()
            .constructParametricType(ArrayList.class, Dept.class);

    List res = objectMapper.readValue(json, type);
    res.forEach(System.out::println);
}

示例：Map序列化和反序列化

public static void main(String[] args) throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();

    Map map = new HashMap();

    map.put("ACCOUNTING",new Dept(10,"ACCOUNTING","CHICAGO"));
    map.put("RESEARCH",new Dept(20,"RESEARCH","DALLAS"));
    map.put("SALES",new Dept(30,"SALES","CHICAGO"));
    map.put("OPERATIONS",new Dept(40,"OPERATIONS","BOSTON"));


    //序列化
    String json = objectMapper.writeValueAsString(map);
    System.out.println(json);

    //反序列化
    JavaType type = objectMapper.getTypeFactory()
            .constructParametricType(HashMap.class, String.class,Dept.class);

    Map res = objectMapper.readValue(json, type);
    res.forEach((k,v)-> System.out.println(k+" : "+v));
}

注解

• JsonIgnore：用于属性上，作用是进行JSON操作时忽略该属性。
• JsonFormat：用于属性上，作用是把Date类型序列化为指定的格式
• JsonProperty：用于属性上，作用是把属性的名称序列化为另外一个名称
• JsonUnwrapped：用于属性上，定义了在序列化/反序列化时应该解包/展开的值，即：把成员对象中的属性提升到其容器类，同时可以添加给定的前缀。
• @JsonSerialize 此注解用于属性上，作用是指定属性序列化的类型。
• @JsonDeserialize 此注解用于属性上，作用是指定属性反序列化的类型。
• @JsonInclude 属性值为null的不参与序列化。
• @JsonInclude(Include.NON_NULL)属性为null，则不参与序列化。
• @JsonPropertyOrder(value={“pname1”,“pname2”}) 改变子属性在JSON序列化中的默认定义的顺序。如：param1在先，param2在后。

示例：注解用法。

• 实体类：

public class Stu {
    @JsonProperty("num")
    private int id;
    private String name;
    @JsonFormat(pattern = "yyyy-MM-dd")
    private Date birth;
    @JsonIgnore
    private float score;
    @JsonUnwrapped(prefix = "addr_")
    private Addr addr;

    public Stu() {
    }

    public Stu(int id, String name, Date birth, float score) {
        this.id = id;
        this.name = name;
        this.birth = birth;
        this.score = score;
    }

    public Stu(int id, String name, Date birth, float score, Addr addr) {
        this.id = id;
        this.name = name;
        this.birth = birth;
        this.score = score;
        this.addr = addr;
    }

    public Addr getAddr() {
        return addr;
    }

    public void setAddr(Addr addr) {
        this.addr = addr;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getBirth() {
        return birth;
    }

    public void setBirth(Date birth) {
        this.birth = birth;
    }

    public float getScore() {
        return score;
    }

    public void setScore(float score) {
        this.score = score;
    }

    @Override
    public String toString() {
        return "Stu{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", birth=" + birth +
                ", score=" + score +
                '}';
    }

    public static class Addr {
        private String province;
        private String city;

        public Addr() {
        }

        public Addr(String province, String city) {
            this.province = province;
            this.city = city;
        }

        public String getProvince() {
            return province;
        }

        public void setProvince(String province) {
            this.province = province;
        }

        public String getCity() {
            return city;
        }

        public void setCity(String city) {
            this.city = city;
        }

        @Override
        public String toString() {
            return "Addr{" +
                    "province='" + province + '\'' +
                    ", city='" + city + '\'' +
                    '}';
        }
    }
}

• 测试代码：

public static void main(String[] args) throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();
    Stu.Addr addr = new Stu.Addr("guizhou", "anshun");
    Stu stu = new Stu(111, "zhangsan", new Date(), 88.8f,addr);
    String json = objectMapper.writeValueAsString(stu);
    System.out.println(json);
}