Java如何使用Jackson格式化LocalDate对象？
我们有一个Recording具有Java8java.time.LocalDate属性的类。我们需要从JSON字符串反序列化此属性并将其序列化。为此，我们可以使用@JsonDeserialize和@JsonSerialize注释来注释该类的LocalDate属性Recording。
@JsonDeserialize(using = LocalDateDeserializer.class) @JsonSerialize(using = LocalDateSerializer.class) private LocalDate releaseDate;
要使用注释，我们需要创建一个类来反序列化和序列化值。要创建一个反序列化器类，我们创建一个extends类StdDeserializer。序列化程序类扩展了StdSerializer该类。下面是LocalDateSerializerandLocalDateDeserializer类的定义。
package org.nhooo.example.jackson;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import java.io.IOException;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
public class LocalDateSerializer extends StdSerializer<LocalDate> {
public LocalDateSerializer() {
super(LocalDate.class);
}
@Override
public void serialize(LocalDate value, JsonGenerator generator, SerializerProvider provider) throws IOException {
generator.writeString(value.format(DateTimeFormatter.ISO_LOCAL_DATE));
}
}package org.nhooo.example.jackson;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import java.io.IOException;
import java.time.LocalDate;
public class LocalDateDeserializer extends StdDeserializer<LocalDate> {
protected LocalDateDeserializer() {
super(LocalDate.class);
}
@Override
public LocalDate deserialize(JsonParser parser, DeserializationContext context) throws IOException {
return LocalDate.parse(parser.readValueAs(String.class));
}
}让我们创建一个简单的类，将Recording对象转换为JSON字符串并应用LocalDateSerializer该类中定义的日期格式程序。
package org.nhooo.example.jackson;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.time.LocalDate;
import java.time.Month;
public class RecordingToJson {
public static void main(String[] args) {
Recording recording = new Recording();
recording.setId(1L);
recording.setTitle("Twist and Shout");
recording.setReleaseDate(LocalDate.of(1964, Month.FEBRUARY, 3));
ObjectMapper mapper = new ObjectMapper();
try {
String json = mapper.writeValueAsString(recording);
System.out.println("JSON = " + json);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}上面的代码片段的输出是：
JSON = {"id":1,"title":"Twist and Shout","releaseDate":"1964-02-03","artist":null,"label":null}这是Recording该类的完整定义。
package org.nhooo.example.jackson;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import java.time.LocalDate;
import java.util.Objects;
public class Recording {
private Long id;
private String title;
@JsonDeserialize(using = LocalDateDeserializer.class)
@JsonSerialize(using = LocalDateSerializer.class)
private LocalDate releaseDate;
private Artist artist;
private Label label;
public Recording() {
}
public Recording(Long id, String title, LocalDate releaseDate) {
this.id = id;
this.title = title;
this.releaseDate = releaseDate;
}
//吸气剂和二传手
}Maven依赖
<!-- http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.8.6</version>
</dependency>