Gson

json.java

public String showJson() throws IOException {
	user = new User();
	user.setId(1001);
	user.setPassword("000000");
	user.setUsername("tom");
		
	response.setContentType("application/json;charset=UTF-8");
	Gson gson = new Gson();
	PrintWriter out = response.getWriter();
	out.print(gson.toJson(user));
	out.flush();
	out.close();
		
	return null;
}