Jackson | Kode Java

How to pretty print JSON string using Jackson?

By Wayan in Jackson Last modified: January 24, 2022 6 Comments

The following example demonstrates how to pretty print the JSON string produces by Jackson library. To produce well formatted JSON string we create the ObjectMapper instance and enable the SerializationFeature.INDENT_OUTPUT feature. To enable this feature we need to call the enable() method of the ObjectMapper and provide the feature to be enabled.

ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
String json = mapper.writeValueAsString(recording);
System.out.println(json);

On the second example below we format unformatted JSON string. To do this we use the ObjectMapper‘s readValue(String, Class<T>) method which accept the JSON string and Object.class as the value type. The readValue() method return an Object. To format the JSON object we call mapper.writerWithDefaultPrettyPrinter().writeValueAsString(Object). This will produce a pretty formatted JSON.

ObjectMapper mapper = new ObjectMapper();
Object jsonObject = mapper.readValue(json, Object.class);
String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);
System.out.println(prettyJson);

Below is the complete code snippets.

package org.kodejava.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.kodejava.jackson.support.Artist;
import org.kodejava.jackson.support.Label;
import org.kodejava.jackson.support.Recording;

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();
        }
    }
}

The code snippet above will pretty print the following JSON string:

{
  "id" : 1,
  "title" : "Yellow Submarine",
  "releaseDate" : "1969-01-17",
  "artist" : {
    "id" : 1,
    "name" : "The Beatles"
  },
  "label" : {
    "id" : 1,
    "name" : "Apple"
  }
}

Here are the structure of Recording, Artist and Label classes.

package org.kodejava.jackson.support;

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import org.kodejava.jackson.LocalDateDeserializer;
import org.kodejava.jackson.LocalDateSerializer;

import java.time.LocalDate;

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;

    // Getters and Setters
}

package org.kodejava.jackson.support;

public class Artist {
    private Long id;
    private String name;

    public Artist() {
    }

    public Artist(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getters and Setters
}

package org.kodejava.jackson.support;

public class Label {
    private Long id;
    private String title;

    public Label(Long id, String title) {
        this.id = id;
        this.title = title;
    }

    // Getters and Setters
}

Maven Dependencies

<dependencies>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.13.1/jackson-core-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.13.1/jackson-databind-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.1</version>
    </dependency>
</dependencies>

How to format LocalDate object using Jackson?

By Wayan in Jackson Last modified: January 24, 2022 4 Comments

We have a Recording class which has a Java 8 java.time.LocalDate property. We need to deserialize and serialize this property from and to JSON string. To do this we can use the @JsonDeserialize and @JsonSerialize annotations to annotate the LocalDate property of the Recording class.

@JsonDeserialize(using = LocalDateDeserializer.class)
@JsonSerialize(using = LocalDateSerializer.class)
private LocalDate releaseDate;

To use the annotation we need to create a class to deserialize and serialize the value. To create a deserializer class we create a class that extends StdDeserializer. The serializer class extends the StdSerializer class. Below is the definition of the LocalDateSerializer and LocalDateDeserializer class.

package org.kodejava.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.kodejava.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));
    }
}

Let’s create a simple class that convert Recording object into JSON string and apply the date formatter defined in the LocalDateSerializer class.

package org.kodejava.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.kodejava.jackson.support.Recording;

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();
        }
    }
}

The output of the code snippet above is:

JSON = {"id":1,"title":"Twist and Shout","releaseDate":"1964-02-03"}

And here is the complete definition of the Recording class.

package org.kodejava.jackson.support;

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import org.kodejava.jackson.LocalDateDeserializer;
import org.kodejava.jackson.LocalDateSerializer;

import java.time.LocalDate;

public class Recording {
    private Long id;
    private String title;

    @JsonDeserialize(using = LocalDateDeserializer.class)
    @JsonSerialize(using = LocalDateSerializer.class)
    private LocalDate releaseDate;

    // Getters and Setters

    @Override
    public String toString() {
        return "Recording{" +
                "id=" + id +
                ", title='" + title + '\'' +
                ", releaseDate=" + releaseDate +
                '}';
    }
}

Maven Dependencies

<dependencies>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.13.1/jackson-core-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.13.1/jackson-databind-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.1</version>
    </dependency>
</dependencies>

How to read and write Java object to JSON file?

By Wayan in Jackson Last modified: January 24, 2022 0 Comment

The following example demonstrate how to serialize and deserialize Java object to JSON file. The Jackson’s ObjectMapper class provides writeValue(File, Object) and readValue(File, Class<T>) methods which allow us to write an object into JSON file and read JSON file into an object respectively.

package org.kodejava.jackson;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.kodejava.jackson.support.Artist;

import java.io.File;
import java.io.IOException;

public class ObjectToJsonFile {
    public static void main(String[] args) {
        Artist artist = new Artist();
        artist.setId(1L);
        artist.setName("The Beatles");

        ObjectMapper mapper = new ObjectMapper();

        File file = new File("artist.json");
        try {
            // Serialize Java object info JSON file.
            mapper.writeValue(file, artist);
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Deserialize JSON file into Java object.
            Artist newArtist = mapper.readValue(file, Artist.class);
            System.out.println("newArtist.getId() = " + newArtist.getId());
            System.out.println("newArtist.getName() = " + newArtist.getName());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The result of the code snippet are:

newArtist.getId() = 1
newArtist.getName() = The Beatles

Maven Dependencies

<dependencies>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.13.1/jackson-core-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.13.1/jackson-databind-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.1</version>
    </dependency>
</dependencies>

How to convert JSON string to Java object?

By Wayan in Jackson Last modified: January 24, 2022 5 Comments

In the following example we will convert JSON string to Java object using ObjectMapper class from the Jackson library. This class provides a method readValue(String, Class<T>) which will deserialize a JSON string into Java object. The first argument to the method is the JSON string and the second parameter is the result type of the conversion.

package org.kodejava.jackson;

import com.fasterxml.jackson.databind.ObjectMapper;
import org.kodejava.jackson.support.Artist;

import java.io.IOException;

public class JsonToObject {
    public static void main(String[] args) {
        String json = """
                {
                    "id": 1,
                    "name": "The Beatles"
                }
                """;

        ObjectMapper mapper = new ObjectMapper();
        try {
            Artist artist = mapper.readValue(json, Artist.class);
            System.out.println("Artist = " + artist);

            System.out.println("artist.getId() = " + artist.getId());
            System.out.println("artist.getName() = " + artist.getName());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

And here is the definition of Artist class.

package org.kodejava.jackson.support;

public class Artist {
    private Long id;
    private String name;

    public Artist() {
    }

    public Artist(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getters & Setters

    @Override
    public String toString() {
        return "Artist{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

The code snippet above will print to following output:

Artist = Artist{id=1, name='The Beatles'}
artist.getId() = 1
artist.getName() = The Beatles

Maven Dependencies

<dependencies>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.13.1/jackson-core-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.13.1/jackson-databind-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.1</version>
    </dependency>
</dependencies>

How to convert Java object to JSON string?

By Wayan in Jackson Last modified: January 24, 2022 1 Comment

The following example shows how to convert Java object into JSON string using Jackson. Jackson provide ObjectMapper class provides functionality to read and write JSON data. The writeValueAsString(Object) method to serialize any Java object into string.

package org.kodejava.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.kodejava.jackson.support.Artist;

public class ObjectToJson {
    public static void main(String[] args) {
        Artist artist = new Artist();
        artist.setId(1L);
        artist.setName("The Beatles");

        ObjectMapper mapper = new ObjectMapper();
        try {
            String json = mapper.writeValueAsString(artist);
            System.out.println("JSON = " + json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

Running the code snippet above will print out the following result:

JSON = {"id":1,"name":"The Beatles"}

And here is the definition of Artist class.

package org.kodejava.jackson.support;

public class Artist {
    private Long id;
    private String name;

    public Artist() {
    }

    public Artist(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getters & Setters

    @Override
    public String toString() {
        return "Artist{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

Maven Dependencies

<dependencies>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.13.1/jackson-core-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.13.1/jackson-annotations-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.13.1</version>
    </dependency>
    <!-- https://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.13.1/jackson-databind-2.13.1.jar -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.13.1</version>
    </dependency>
</dependencies>