package yanagishima.util;

import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.http.HttpServletResponse;

import org.apache.http.entity.ContentType;
import org.codehaus.jackson.map.ObjectMapper;

public final class JsonUtil {
	private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

	private JsonUtil() {}

	public static void writeJSON(HttpServletResponse response, Object obj) {
		try {
			response.setContentType(ContentType.APPLICATION_JSON.getMimeType());
			OutputStream stream = response.getOutputStream();
			OBJECT_MAPPER.writeValue(stream, obj);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}
}

package yanagishima.util;

import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.http.HttpServletResponse;

import org.apache.http.entity.ContentType;
import org.codehaus.jackson.map.ObjectMapper;

public final class JsonUtil {
	private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

	private JsonUtil() {}

	public static void writeJSON(HttpServletResponse response, Object obj) {
		response.setContentType(ContentType.APPLICATION_JSON.getMimeType());
		try (OutputStream stream = response.getOutputStream()) {
			OBJECT_MAPPER.writeValue(stream, obj);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}
}

Use try-with-resources in JsonUtil