exemple json

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.google.common.io.Files;

import java.io.File;
import java.io.IOException;
import java.io.StringWriter;
import java.nio.charset.Charset;
import java.util.Arrays;

/**
 * @author Manuel Boillod
 */
public class JsonUtils {

    public static String toJson(Object object) {
        StringWriter stringWriter = new StringWriter();
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);
        mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS, true);
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        try {
            mapper.writeValue(stringWriter, object);
            return stringWriter.toString();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public static void toFile(String content, String filename) {
        toFile(content, new File(filename));
    }

    public static void toFile(String content, File file) {
        try {
            Files.write(content,
                    file,
                    Charset.defaultCharset());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

Better use UTF-8 instead of defaultCharset, to avoid issues moving between different platforms with different encodings.