code: public void render(Map<?, ?> data, Writer writer) {
  		CharWriter charWriter = env.engineConfig.writerBuffer.getCharWriter(writer);
  		try {
  			ast.exec(env, new Scope(data, env.engineConfig.sharedObjectMap), charWriter);
  		} finally {
  			charWriter.close();
  		}
  	}
docs: 渲染到 Writer 中去