How do annotations in the Jackson library control JSON serialization and deserialization?

Annotations in the Jackson library control JSON serialization and deserialization: Serialization: @JsonIgnore: Ignore the property @JsonProperty: Specify the name @JsonGetter: Use the get method @JsonSetter: Use the set method Deserialization: @JsonIgnoreProperties: Ignore the property @JsonProperty: Specify the name @JsonCreator: Use the constructor @JsonDeserialize: Custom logic

Annotations are used in the Jackson library to control JSON serialization and deserialization

Introduction

The Jackson library is a popular Java library for binding JSON data. Annotations play a vital role in the Jackson library, allowing us to control the JSON serialization and deserialization process.

Serialization annotations

• @JsonIgnore: Ignore a property or method so that it is not included in the JSON output.
• @JsonProperty: Specifies the name of the property in the JSON output.
• @JsonGetter: Get the value returned when the method is called instead of accessing the property directly.
• @JsonSetter: Set the value of the property when the setter method is called, rather than assigning the value directly.

Deserialization annotations

• @JsonIgnoreProperties: Ignore the properties specified in the JSON input.
• @JsonProperty: Specify the name of the property in the JSON input and map it to a property or method.
• @JsonCreator: Create objects using non-default constructors instead of using setter methods.
• @JsonDeserialize: Specify custom deserialization logic, you can use a custom type converter or handler.

Practical case

The following is an example class showing how to use Jackson annotations:

@JsonIgnoreProperties(ignoreUnknown = true)
public class Person {

    private String name;

    @JsonProperty("age")
    private int yearsOld;

    @JsonGetter("education")
    public String getEducation() {
        return "College";
    }

    @JsonSetter("years_old")
    public void setAge(int yearsOld) {
        this.yearsOld = yearsOld;
    }
}

In this example:

• @JsonIgnoreProperties(ignoreUnknown = true) Ignore properties that do not exist in the class in the JSON input.
• @JsonProperty("age") Specifies that the name of the yearsOld property in the JSON output is "age".
• @JsonGetter("education") Returns the value of the "education" attribute through the get method "getEducation".
• @JsonSetter("years_old") Set the value of the "yearsOld" attribute through the setting method "setAge".

You can use the Jackson library for serialization and deserialization in the following ways:

// 序列化
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(person);

// 反序列化
Person person = mapper.readValue(json, Person.class);

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