1.从Java EE5规范开始，Servlet中增加了两个影响Servlet生命周期的注解，
@PostConstruct和@PreDestroy，这两个注解被用来修饰一个非静态的void（）方法，被@PostConstruct修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器执行一次。PostConstruct在构造函数之后执行，init（）方法之前执行。PreDestroy（）方法在destroy（）方法执行之后执行。2.执行顺序
spring中Constructor、@Autowired、@PostConstruct的顺序执行。3.实现样例import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

/*** description: 基础数据缓存 
* version: 1.0 
*/
@Component
public class CodeCache {

//基础字典表数据
public static List tabBaseDicList = new ArrayList<>();
public static Map> tabBaseDicMap = new HashMap>();
public static Map> typeBaseDicMap = new HashMap<>();

/*** 查询基础数据**/
@PostConstruct
public void init(){
//基础字典表数据
QueryWrapper queryBaseDicWrapper = new QueryWrapper<>();
queryBaseDicWrapper.isNotNull("type");
queryBaseDicWrapper.eq("delete_flag", Const.DELETE_FLAG_NOMAL);
tabBaseDicList = tabBaseDicMapper.selectList(queryBaseDicWrapper);
typeBaseDicMap = tabBaseDicList.stream().collect(Collectors.groupingBy(TabBaseDic::getType));
}

@PreDestroy
public void destroy(){}

}