mybatis緩存機制

一級緩存
	會話級緩存，SqlSession 級別，默認是開啓

	清除一級緩存對象
	commit();
	session.clearCache(); 
		    
	    @Test
	    public void query() {
		BookMapper bm = session.getMapper(BookMapper.class);
		System.out.println(bm.queryAll());
		System.out.println(bm.queryAll());//一級緩存
		session.commit();
		System.out.println(bm.queryById(3));
		//session.clearCache();
		System.out.println(bm.queryById(3));//一級緩存
		//session.commit();
		System.out.println(bm.queryById(3));
		System.out.println(bm.queryById(3));
	    }

二級緩存
	SqlSessionFactory級別緩存，會話工廠級別
		SqlSession s1 = sf.openSession();
		SqlSession s2 = sf.openSession();
		SqlSession s3 = sf.openSession();
		System.out.println(s1);
		System.out.println(s2);
		System.out.println(s3);
	開發者必須自己配置二級緩存
	二級緩存是人工開啓的，需要在XxxxMapper.xml 文件中加入如下開啓
	   方法一
		    <cache eviction="FIFO" flushInterval="60000" size="5120" readOnly="true" />
		    <select id="queryAll" resultType="book" useCache="false">  默認使用緩存，填寫false此操作不讓緩存
			select * from book
		    </select>

	   方法二
			@CacheNamespace(eviction = FifoCache.class, flushInterval = 60000, size = 1024, readWrite = true)
			public interface BookMapper {
			    @Select("select * from book") @Options(useCache = true)
			    public List<Book> queryAll();

			    @Select("select * from book where id = #{id}")
			    public Book queryById(int id);
			}	   	

	注意：使用緩存時，最好給實體類序列化。

	java是什麼是序列化？會什麼不序列化？
    

	測試代碼爲：
	   @Test
	    public void ccc() throws IOException, ClassNotFoundException {
		SqlSession s1 = sf.openSession();
		SqlSession s3 = sf.openSession();
		//一級緩存
		//BookMapper bm1 = s1.getMapper(BookMapper.class);
		//BookMapper bm2 = s1.getMapper(BookMapper.class);
		//System.out.println(bm1.queryAll());
		//System.out.println(bm2.queryAll());
		//二級緩存
		BookMapper bm1 = s1.getMapper(BookMapper.class);
		//bm1.queryById(3);
		System.out.println(bm1.queryAll());
		s1.commit();//二級緩存才生效

		//sf.getConfiguration().getCaches().clear();
		//s1.getConfiguration().getCaches().clear();
		sf.getConfiguration().getCaches().clear();;

		SqlSession s2 = sf.openSession();
		BookMapper bm2 = s2.getMapper(BookMapper.class);
		System.out.println(bm2.queryAll());//讀取二級緩存

		//Book bk = new Book();
		//bk.setId(1000);
		//bk.setPrice(80);
		//bk.setName("《java開發入門》");

		//請把bk保存到硬盤上,首先確認bk實現序列化接口
		//ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("c:/a.dat"));
		//oos.writeObject(bk);
		//oos.close();

		//反序列化
		//ObjectInputStream ois = new ObjectInputStream(new FileInputStream("c:/a.dat"));
		//Book bk = (Book)ois.readObject();
		//System.out.println(bk);
		//System.out.println(bk.getName());
	    }