flink-处理json

ObjectMapper 各个方法的示例：

1. `readTree(String json)`

该方法将 JSON 字符串解析为 JsonNode 对象。这允许你以树形结构来访问 JSON 数据。

示例：

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Example {
    public static void main(String[] args) throws Exception {
        String jsonString = "{\"name\": \"John\", \"age\": 30}";

        ObjectMapper objectMapper = new ObjectMapper();
        JsonNode rootNode = objectMapper.readTree(jsonString);

        // 访问 JSON 数据
        String name = rootNode.get("name").asText();
        int age = rootNode.get("age").asInt();

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }
}

输出：

1 2	Name: John Age: 30

2. `writeValueAsString(Object value)`

该方法将 Java 对象转换为 JSON 字符串。

示例：

import com.fasterxml.jackson.databind.ObjectMapper;

public class Example {
    public static void main(String[] args) throws Exception {
        Person person = new Person("John", 30);

        ObjectMapper objectMapper = new ObjectMapper();
        String jsonString = objectMapper.writeValueAsString(person);

        System.out.println(jsonString);
    }
}

class Person {
    private String name;
    private int age;

    // 构造函数、getter 和 setter
    public Person() {}
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    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; }
}

输出：

1	{"name":"John","age":30}

3. `readValue(String json, Class<T> valueType)`

该方法将 JSON 字符串转换为指定类型的 Java 对象。

示例：

import com.fasterxml.jackson.databind.ObjectMapper;

public class Example {
    public static void main(String[] args) throws Exception {
        String jsonString = "{\"name\": \"John\", \"age\": 30}";

        ObjectMapper objectMapper = new ObjectMapper();
        Person person = objectMapper.readValue(jsonString, Person.class);

        System.out.println("Name: " + person.getName());
        System.out.println("Age: " + person.getAge());
    }
}

class Person {
    private String name;
    private int age;

    // 构造函数、getter 和 setter
    public Person() {}
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    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; }
}