@PostConstruct和@PostConstruct 注解 及ehcache 缓存 执行过程 小记

@PostConstruct 和@PostConstruct 注解

从Java EE 5规范开始，Servlet中增加了两个影响Servlet生命周期的注解（Annotion）；@PostConstruct和@PreDestroy。这两个注解被用来修饰一个非静态的void()方法 。写法有如下两种方式：

@PostConstruct

Public void someMethod() {}                                                                                     

或者

public @PostConstruct void someMethod(){}

被@PostConstruct修饰的方法会在服务器加载Servle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()方法执行执行之后执行。

ehcache 缓存 执行过程

加载servlet时，

通过initCache方法读取缓存配置文件来构建缓存实例

@PostConstruct
    void initCache() {
        logger = Logger.getLogger(getClass());
        if (getCache() == null) {
            String clsName = getClass().getSimpleName();
            URL url = getClass().getResource(
                    SystemGlobals.getValue('/xx/ehcache.xml'));
            CacheManager manager = CacheManager.create(url);
            Cache c = manager.getCache(clsName);
            setCache(c);
        }
        if (logger.isDebugEnabled()) {
            logger.debug("初始化:" + getCache());
        }

    }

构建实例后，需一次性加载缓存数据

@PostConstruct
    void init() {
        if (!isInitCategory) {
            initCategories();
            isInitCategory = true;
        }
        if (!isInitBrand) {
            initBrands();
            isInitBrand = true;
        }
    }

    private void initCategories() {
        Range<Category> range = categoryDao.select();
        categoryCache.putAll(range.getData());

    }
    public void putAll(Collection<Category> categories) {
      List<Category> list = new ArrayList<Category>(categories);

      Element element = new Element(FQN_ALL, list);
      cache.removeAll();
      cache.put(element);
   }

项目启动后，访问项目，读取缓存数据

        private static Cache cache;

    private static final String FQN_ALL = "all";
    private static final String FQN_KEY = "key";
    private static final String FQN_CHILDREN = "children";
    private static final String FQN_ROOT = "root";
@SuppressWarnings("unchecked")
    public Collection<Category> root() {
        String key = FQN_ROOT;
        Element element = cache.get(key);
        if (element != null) {
            return (List<Category>) element.getValue();
        }
        List<Category> root = new ArrayList<Category>();
        List<Category> categories = getCategories();
        for (Category category : categories) {
            if (category.isRoot()) {
                root.add(category);
            }
        }
        element = new Element(key, root);
        cache.put(element);
        return root;
    }

@SuppressWarnings("unchecked")
    private List<Category> getCategories() {
        Element element = cache.get(FQN_ALL);
        if (element != null) {
            return (List<Category>) element.getValue();
        }
        return new ArrayList<Category>(0);
    }