本篇文章给大家分享的是有关Mybatis中缓存的方式有哪些,小编觉得挺实用的,因此分享给大家学习,希望大家阅读完这篇文章后可以有所收获,话不多说,跟着小编一起来看看吧。
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mybatis默认sqlsession:org.apache.ibatis.session.defaults.DefaultSqlSession
构造方法中传入executor(查询执行对象)
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) { this.configuration = configuration; this.executor = executor; this.dirty = false; this.autoCommit = autoCommit; }
executor中携带一级缓存成员:
protected BaseExecutor(Configuration configuration, Transaction transaction) { this.transaction = transaction; this.deferredLoads = new ConcurrentLinkedQueue<>(); this.localCache = new PerpetualCache("LocalCache"); //默认一级缓存 this.localOutputParameterCache = new PerpetualCache("LocalOutputParameterCache"); this.closed = false; this.configuration = configuration; this.wrapper = this; }
org.apache.ibatis.executor.BaseExecutor.query()
publicList query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId()); List list; try { queryStack++; //localCache 一级缓存 list = resultHandler == null ? (List ) localCache.getObject(key) : null; //先从一级缓存中获取,key是通过sql语句生成 if (list != null) { handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); } else { // 如果缓存中没有 才从数据库查询 list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); } } finally { queryStack--; } return list; } //从数据库读取数据 private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { List list; localCache.putObject(key, EXECUTION_PLACEHOLDER); try { list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql); } finally { localCache.removeObject(key);//将一级缓存清除 } localCache.putObject(key, list);//返回查询结果之前,先放入一级缓存 刷新 if (ms.getStatementType() == StatementType.CALLABLE) { localOutputParameterCache.putObject(key, parameter); } return list; }
二级缓存mapper中的,默认是开启的,但需要在映射文件mapper.xml中添加
配置false可以关闭二级缓存
org.apache.ibatis.builder.xml.XMLMapperBuilder
private void configurationElement(XNode context) { try { //... cacheElement(context.evalNode("cache")); //解析cache标签 } catch (Exception e) { throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e); } } private void cacheElement(XNode context) { if (context != null) { // if hava cache tag 如果有cache标签才执行下面的逻辑 String type = context.getStringAttribute("type", "PERPETUAL"); Class extends Cache> typeClass = typeAliasRegistry.resolveAlias(type); String eviction = context.getStringAttribute("eviction", "LRU"); Class extends Cache> evictionClass = typeAliasRegistry.resolveAlias(eviction); Long flushInterval = context.getLongAttribute("flushInterval"); Integer size = context.getIntAttribute("size"); boolean readWrite = !context.getBooleanAttribute("readOnly", false); boolean blocking = context.getBooleanAttribute("blocking", false); Properties props = context.getChildrenAsProperties(); builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props);//建立二级缓存 } }
org.apache.ibatis.builder.MapperBuilderAssistant.useNewCache():
public Cache useNewCache(Class extends Cache> typeClass, Class extends Cache> evictionClass, Long flushInterval, Integer size, boolean readWrite, boolean blocking, Properties props) { Cache cache = new CacheBuilder(currentNamespace) .implementation(valueOrDefault(typeClass, PerpetualCache.class)) .addDecorator(valueOrDefault(evictionClass, LruCache.class)) .clearInterval(flushInterval) .size(size) .readWrite(readWrite) .blocking(blocking) .properties(props) .build(); configuration.addCache(cache);//二级缓存赋值,如果cache标签为空,不会执行此方法,currentCache为空 currentCache = cache; return cache; }
在映射文件mapper中如果没有cache标签,不会执行上面的useNewCache方法,cache为null,就不会使用二级缓存(相当于失效)。
org.apache.ibatis.executor.CachingExecutor :
@Override publicList query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { Cache cache = ms.getCache(); if (cache != null) {//如果二级缓存对象不为空 尝试在二级缓存中获取(没有cache标签此对象就是空) flushCacheIfRequired(ms); if (ms.isUseCache() && resultHandler == null) { ensureNoOutParams(ms, boundSql); @SuppressWarnings("unchecked") List list = (List ) tcm.getObject(cache, key); //从二级缓存中获取数据 if (list == null) { list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); //如果为空,使用delegate查询(BaseExecutor) tcm.putObject(cache, key, list); // 查询结果保存到二级缓存 } return list; } } return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }
二级缓存和一级缓存不用想,数据库的数据被修改是要清空缓存的,不然数据有误,至于怎么清空,是另一套逻辑了,mapper中的cache标签可以配置一些参数,比如缓存定期清空。
mybatis默认是先查询二级缓存,没有,再查看一级缓存,都为空,最后查询数据库
以上就是Mybatis中缓存的方式有哪些,小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注创新互联行业资讯频道。