File output bean as JSON in spring

pom.xml

pom.xml

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.1.RELEASE</version>
	</parent>
	<dependencies>
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
		</dependency>
	</dependencies>

File output using ObjectWriter

package kagamihoge.tojsonfile;

import java.nio.file.Paths;
import java.util.Arrays;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;

import lombok.AllArgsConstructor;
import lombok.Data;

@SpringBootApplication
public class BeanToJsonFileApplication implements CommandLineRunner {
	public static void main(String[] args) throws InterruptedException {
		SpringApplication.run(BeanToJsonFileApplication.class, args).close();
	}

	@Bean
	public ObjectWriter writer() {
		ObjectMapper mapper = new ObjectMapper();
		ObjectWriter writer = mapper.writer(new DefaultPrettyPrinter());
		return writer;
	}

	@Autowired
	ObjectWriter writer;

	@Override
	public void run(String... args) throws Exception {
		List<Sub> subList = Arrays.asList(new Sub(1, true), new Sub(2, true));
		Top top = new Top("hogeId", null, subList);

		writer.writeValue(Paths.get("json.txt").toFile(), top);
	}

	@Data
	@AllArgsConstructor
	static class Top {
		private String hogeId;
		private String nullValue;
		private List<Sub> subList;
	}

	@Data
	@AllArgsConstructor
	static class Sub {
		private int subId;
		private boolean bool;
	}
}

Output example

{
  "hogeId" : "hogeId",
  "nullValue" : null,
  "subList" : [ {
    "subId" : 1,
    "bool" : true
  }, {
    "subId" : 2,
    "bool" : true
  } ]
}

Other control items

It's basically jackson, so if you have something else you want to do, it usually comes out.

The following is an example.

Convert key from camel case to snake case

import com.fasterxml.jackson.databind.PropertyNamingStrategy;

mapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);

Output example.

{
  "hoge_id" : "hogeId",
  "null_value" : null,
  "sub_list" : [ {
    "sub_id" : 1,
    "bool" : true
  }, {
    "sub_id" : 2,
    "bool" : true
  } ]
}

Change the key to any value

@JsonProperty("alternateId")
private String hogeId;

Output as String

System.out.println(writer.writeValueAsString(top));

If you don't need JSON formatting

import com.fasterxml.jackson.core.util.MinimalPrettyPrinter;

ObjectWriter writer = mapper.writer(new MinimalPrettyPrinter());

Output example.

{"null_value":null,"sub_list":[{"sub_id":1,"bool":true},{"sub_id":2,"bool":true}],"alternateId":"hogeId"}