FlushMode

NEVER

public static final FlushMode NEVER

Deprecated. use MANUAL instead.

The Session is never flushed unless Session.flush() is explicitly called by the application. This mode is very efficient for read only transactions.

MANUAL

public static final FlushMode MANUAL

The Session is only ever flushed when Session.flush() is explicitly called by the application. This mode is very efficient for read only transactions.

COMMIT

public static final FlushMode COMMIT

The Session is flushed when Transaction.commit() is called.

AUTO

public static final FlushMode AUTO

The Session is sometimes flushed before query execution in order to ensure that queries never return stale state. This is the default flush mode.

ALWAYS

public static final FlushMode ALWAYS

             The Session is flushed before every query. This is almost always unnecessary and inefficient.

1、NEVER
        已经废弃了，被MANUAL取代了
2、MANUAL 
        spring3.x中的opensessioninviewfilter已经将默认的FlushMode设置为MANUAL了；如果FlushMode是MANUAL或NEVER,在操作过程中hibernate会将事务设置为readonly，所以在增加、删除或修改操作过程中会出现如下错误
org.springframework.dao.InvalidDataAccessApiUsageException: Write operations are not allowed in read-only mode (FlushMode.NEVER) - turn your Session into FlushMode.AUTO or remove 'readOnly' marker from transaction definition；
解决办法；
1 配置事务，spring会读取事务中的各种配置来覆盖hibernate的session中的FlushMode；
2 先编程式修改FlushMode，比如session.setFlushMode(FlushMode.AUTO); 这样hibernate就会自动去除readonly限制；
3 直接修改opensessioninviewfilter过滤器的配置，配置过滤器的时候配置
<filter>
      <filter-name>openSession</filter-name>
      <filter-class>org.springframework.orm.hibernate3.support.OpenSessionInViewFilter</filter-class>
      <init-param>
          <param-name>flushMode</param-name>
          <param-value>AUTO</param-value>
      </init-param>
</filter>
3、AUTO
       设置成auto之后，当程序进行查询、提交事务或者调用session.flush()的时候，都会使缓存和数据库进行同步，也就是刷新数据库

4、COMMIT
       提交事务或者session.flush()时，刷新数据库；查询不刷新
5、ALWAYS
       每次进行查询、提交事务、session.flush()的时候都会刷数据库,和AUTO的区别，当hibernate缓存中的对象被改动之后，会被标记为脏数据（即与数据库不同步了）。当session设置为FlushMode.AUTO时，hibernate在进行查询的时候会判断缓存中的数据是否为脏数据，是则刷数据库，不是则不刷，而ALWAYS是直接刷新，不进行任何判断。