Java如何使用Jackson轻松打印JSON字符串？
下面的示例演示如何漂亮地打印Jackson库生成的JSON字符串。为了产生格式正确的JSON字符串，我们创建ObjectMapper实例并启用该SerializationFeature.INDENT_OUTPUT功能。要启用此功能，我们需要调用的enable()方法ObjectMapper并提供要启用的功能。
ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT); String json = mapper.writeValueAsString(recording); System.out.println(json);
在下面的第二个示例中，我们格式化未格式化的JSON字符串。为此，我们使用ObjectMapper的readValue(String,Class<T>)方法，该方法接受JSON字符串Object.class作为值类型。该readValue()方法返回Object。要格式化JSON对象，我们调用mapper.writerWithDefaultPrettyPrinter().writeValueAsString(Object)。这将产生一个漂亮的JSON格式。
ObjectMapper mapper = new ObjectMapper(); Object jsonObject = mapper.readValue(json, Object.class); String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject); System.out.println(prettyJson);
以下是完整的代码段。
package org.nhooo.example.jackson;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import java.io.IOException;
import java.time.LocalDate;
import java.time.Month;
public class JsonIndentOutput {
public static void main(String[] args) {
JsonIndentOutput.formatObjectToJsonString();
JsonIndentOutput.formatJsonString();
}
private static void formatObjectToJsonString() {
Recording recording = new Recording();
recording.setId(1L);
recording.setTitle("Yellow Submarine");
recording.setReleaseDate(LocalDate.of(1969, Month.JANUARY, 17));
recording.setArtist(new Artist(1L, "The Beatles"));
recording.setLabel(new Label(1L, "Apple"));
ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
try {
String json = mapper.writeValueAsString(recording);
System.out.println(json);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
private static void formatJsonString() {
String json = "{\"id\":1,\"title\":\"Yellow Submarine\",\"releaseDate\":\"1969-01-17\",\"artist\":{\"id\":1,\"name\":\"The Beatles\"},\"label\":{\"id\":1,\"name\":\"Apple\"}}";
ObjectMapper mapper = new ObjectMapper();
try {
Object jsonObject = mapper.readValue(json, Object.class);
String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);
System.out.println(prettyJson);
} catch (IOException e) {
e.printStackTrace();
}
}
}上面的代码片段将漂亮地打印以下JSON字符串：
{
"id" : 1,
"title" : "Yellow Submarine",
"releaseDate" : "1969-01-17",
"artist" : {
"id" : 1,
"name" : "The Beatles"
},
"label" : {
"id" : 1,
"name" : "Apple"
}
}这是Recording类的结构。
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>