myBatis源码之Executor、BaseExecutor和CachingExecutor
接下来是mybatis的执行过程,mybatis提供了一个接口Executor,Executor接口主要提供了update、query方法及事物相关的方法接口
/** * @author Clinton Begin */ public interface Executor { ResultHandler NO_RESULT_HANDLER = null; /* 更新操作**/ int update(MappedStatement ms, Object parameter) throws SQLException; <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey cacheKey, BoundSql boundSql) throws SQLException; <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException; List<BatchResult> flushStatements() throws SQLException; void commit(boolean required) throws SQLException; void rollback(boolean required) throws SQLException; CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql); boolean isCached(MappedStatement ms, CacheKey key); void clearLocalCache(); void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType); Transaction getTransaction(); void close(boolean forceRollback); boolean isClosed(); void setExecutorWrapper(Executor executor); }
接下来是Executor的两个子类:抽象类BaseExecutor和CachingExecutor。
抽象类BaseExecutor采用模板方法设计模式,具体的实现在其子类:BatchExecutor、ReuseExecutor和SimpleExecutor,接下来会详细进行介绍。
BaseExecutor:
/** * @author Clinton Begin */ public abstract class BaseExecutor implements Executor { private static final Log log = LogFactory.getLog(BaseExecutor.class); //事务 protected Transaction transaction; //executor protected Executor wrapper; //线程安全队列 protected ConcurrentLinkedQueue<DeferredLoad> deferredLoads; //缓存 永久缓存 本地缓存 protected PerpetualCache localCache; // protected PerpetualCache localOutputParameterCache; //mybatis的配置信息 protected Configuration configuration; //查询堆栈 protected int queryStack = 0; private boolean closed; //构造函数 protected BaseExecutor(Configuration configuration, Transaction transaction) { this.transaction = transaction; this.deferredLoads = new ConcurrentLinkedQueue<DeferredLoad>(); this.localCache = new PerpetualCache("LocalCache"); this.localOutputParameterCache = new PerpetualCache("LocalOutputParameterCache"); this.closed = false; this.configuration = configuration; this.wrapper = this; } public Transaction getTransaction() { if (closed) throw new ExecutorException("Executor was closed."); return transaction; } public void close(boolean forceRollback) { try { try { rollback(forceRollback); } finally { if (transaction != null) transaction.close(); } } catch (SQLException e) { // Ignore. There's nothing that can be done at this point. log.warn("Unexpected exception on closing transaction. Cause: " + e); } finally { transaction = null; deferredLoads = null; localCache = null; localOutputParameterCache = null; closed = true; } } public boolean isClosed() { return closed; } //SqlSession的update/insert/delete会调用此方法 public int update(MappedStatement ms, Object parameter) throws SQLException { ErrorContext.instance().resource(ms.getResource()).activity("executing an update").object(ms.getId()); if (closed) throw new ExecutorException("Executor was closed."); //先清局部缓存,再更新,如何更新由子类实现,模板方法模式 clearLocalCache(); return doUpdate(ms, parameter); } public List<BatchResult> flushStatements() throws SQLException { return flushStatements(false); } public List<BatchResult> flushStatements(boolean isRollBack) throws SQLException { if (closed) throw new ExecutorException("Executor was closed."); return doFlushStatements(isRollBack); } //SqlSession.selectList会调用此方法 public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { //得到绑定sql BoundSql boundSql = ms.getBoundSql(parameter); //创建缓存key CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql); //查询 return query(ms, parameter, rowBounds, resultHandler, key, boundSql); } @SuppressWarnings("unchecked") public <E> List<E> 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()); //如果已经关闭,报错 if (closed) throw new ExecutorException("Executor was closed."); //先清局部缓存,再查询,但仅仅查询堆栈为0才清,为了处理递归调用 if (queryStack == 0 && ms.isFlushCacheRequired()) { clearLocalCache(); } List<E> list; try { //加一,这样递归调用到上面的时候就不会再清局部缓存了 queryStack++; //根据cachekey从localCache去查 list = resultHandler == null ? (List<E>) localCache.getObject(key) : null; if (list != null) { //如果查到localCache缓存,处理localOutputParameterCache handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); } else { //从数据库查 list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); } } finally { //清空堆栈 queryStack--; } if (queryStack == 0) { //延迟加载队列中所有元素 for (DeferredLoad deferredLoad : deferredLoads) { deferredLoad.load(); } //清空延迟加载队列 deferredLoads.clear(); // issue #601 if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { //如果是statement,清本地缓存 clearLocalCache(); // issue #482 } } return list; } //延迟加载 public void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType) { if (closed) throw new ExecutorException("Executor was closed."); DeferredLoad deferredLoad = new DeferredLoad(resultObject, property, key, localCache, configuration, targetType); //如果能加载则立即加载,否则加入到延迟加载队列中 if (deferredLoad.canLoad()) { deferredLoad.load(); } else { //这里怎么又new了一个新的,性能有点问题 deferredLoads.add(new DeferredLoad(resultObject, property, key, localCache, configuration, targetType)); } } //创建缓存key public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) { if (closed) throw new ExecutorException("Executor was closed."); CacheKey cacheKey = new CacheKey(); //MyBatis 对于其 Key 的生成采取规则为:[mappedStementId + offset + limit + SQL + queryParams + environment]生成一个哈希码 cacheKey.update(ms.getId()); cacheKey.update(rowBounds.getOffset()); cacheKey.update(rowBounds.getLimit()); cacheKey.update(boundSql.getSql()); List<ParameterMapping> parameterMappings = boundSql.getParameterMappings(); TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry(); for (int i = 0; i < parameterMappings.size(); i++) { // mimic DefaultParameterHandler logic ParameterMapping parameterMapping = parameterMappings.get(i); if (parameterMapping.getMode() != ParameterMode.OUT) { Object value; String propertyName = parameterMapping.getProperty(); if (boundSql.hasAdditionalParameter(propertyName)) { value = boundSql.getAdditionalParameter(propertyName); } else if (parameterObject == null) { value = null; } else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) { value = parameterObject; } else { MetaObject metaObject = configuration.newMetaObject(parameterObject); value = metaObject.getValue(propertyName); } cacheKey.update(value); } } return cacheKey; } public boolean isCached(MappedStatement ms, CacheKey key) { return localCache.getObject(key) != null; } public void commit(boolean required) throws SQLException { if (closed) throw new ExecutorException("Cannot commit, transaction is already closed"); clearLocalCache(); flushStatements(); if (required) { transaction.commit(); } } public void rollback(boolean required) throws SQLException { if (!closed) { try { clearLocalCache(); flushStatements(true); } finally { if (required) { transaction.rollback(); } } } } //清空本地缓存,一个map结构 public void clearLocalCache() { if (!closed) { localCache.clear(); localOutputParameterCache.clear(); } } protected abstract int doUpdate(MappedStatement ms, Object parameter) throws SQLException; protected abstract List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException; protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException; protected void closeStatement(Statement statement) { if (statement != null) { try { statement.close(); } catch (SQLException e) { // ignore } } } //处理存储过程的out参数 private void handleLocallyCachedOutputParameters(MappedStatement ms, CacheKey key, Object parameter, BoundSql boundSql) { if (ms.getStatementType() == StatementType.CALLABLE) { final Object cachedParameter = localOutputParameterCache.getObject(key); if (cachedParameter != null && parameter != null) { final MetaObject metaCachedParameter = configuration.newMetaObject(cachedParameter); final MetaObject metaParameter = configuration.newMetaObject(parameter); for (ParameterMapping parameterMapping : boundSql.getParameterMappings()) { if (parameterMapping.getMode() != ParameterMode.IN) { final String parameterName = parameterMapping.getProperty(); final Object cachedValue = metaCachedParameter.getValue(parameterName); metaParameter.setValue(parameterName, cachedValue); } } } } } //从数据库中查 private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { List<E> list; //向缓存中放入占位符 localCache.putObject(key, EXECUTION_PLACEHOLDER); try { list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql); } finally { //清除占位符 localCache.removeObject(key); } //加入缓存 localCache.putObject(key, list); //如果是存储过程,OUT参数也加入缓存 if (ms.getStatementType() == StatementType.CALLABLE) { localOutputParameterCache.putObject(key, parameter); } return list; } protected Connection getConnection(Log statementLog) throws SQLException { Connection connection = transaction.getConnection(); if (statementLog.isDebugEnabled()) { return ConnectionLogger.newInstance(connection, statementLog, queryStack); } else { return connection; } } public void setExecutorWrapper(Executor wrapper) { this.wrapper = wrapper; } //延迟加载 private static class DeferredLoad { private final MetaObject resultObject; private final String property; private final Class<?> targetType; private final CacheKey key; private final PerpetualCache localCache; private final ObjectFactory objectFactory; private final ResultExtractor resultExtractor; public DeferredLoad(MetaObject resultObject, String property, CacheKey key, PerpetualCache localCache, Configuration configuration, Class<?> targetType) { // issue #781 this.resultObject = resultObject; this.property = property; this.key = key; this.localCache = localCache; this.objectFactory = configuration.getObjectFactory(); this.resultExtractor = new ResultExtractor(configuration, objectFactory); this.targetType = targetType; } //缓存中找到,且不为占位符,代表可以加载 public boolean canLoad() { return localCache.getObject(key) != null && localCache.getObject(key) != EXECUTION_PLACEHOLDER; } //加载 public void load() { @SuppressWarnings( "unchecked" ) // we suppose we get back a List List<Object> list = (List<Object>) localCache.getObject(key); Object value = resultExtractor.extractObjectFromList(list, targetType); resultObject.setValue(property, value); } } }
CachingExecutor:CachingExecutor 从内存中获取数据,在查找数据库前先查找缓存,若没有找到的话调用delegate从数据库查询,并将查询结果存入缓存中。
/** * @author Clinton Begin * @author Eduardo Macarron */ public class CachingExecutor implements Executor { private Executor delegate; private TransactionalCacheManager tcm = new TransactionalCacheManager(); public CachingExecutor(Executor delegate) { this.delegate = delegate; delegate.setExecutorWrapper(this); } public Transaction getTransaction() { return delegate.getTransaction(); } public void close(boolean forceRollback) { try { //issues #499, #524 and #573 if (forceRollback) { tcm.rollback(); } else { tcm.commit(); } } finally { delegate.close(forceRollback); } } //是否关闭了executor public boolean isClosed() { return delegate.isClosed(); } public int update(MappedStatement ms, Object parameterObject) throws SQLException { //是否需要更缓存 flushCacheIfRequired(ms); //更新数据 return delegate.update(ms, parameterObject); } public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { BoundSql boundSql = ms.getBoundSql(parameterObject); //创建缓存值 CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql); //获取记录 return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { //获取缓存 Cache cache = ms.getCache(); if (cache != null) { flushCacheIfRequired(ms); if (ms.isUseCache() && resultHandler == null) { ensureNoOutParams(ms, parameterObject, boundSql); @SuppressWarnings("unchecked") //从缓存中获取数据 List<E> list = (List<E>) tcm.getObject(cache, key); //为空执行一次,将结果保存到缓存中 if (list == null) { list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); tcm.putObject(cache, key, list); // issue #578. Query must be not synchronized to prevent deadlocks } return list; } } return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } public List<BatchResult> flushStatements() throws SQLException { return delegate.flushStatements(); } public void commit(boolean required) throws SQLException { delegate.commit(required); tcm.commit(); } public void rollback(boolean required) throws SQLException { try { delegate.rollback(required); } finally { if (required) { tcm.rollback(); } } } private void ensureNoOutParams(MappedStatement ms, Object parameter, BoundSql boundSql) { if (ms.getStatementType() == StatementType.CALLABLE) { for (ParameterMapping parameterMapping : boundSql.getParameterMappings()) { if (parameterMapping.getMode() != ParameterMode.IN) { throw new ExecutorException("Caching stored procedures with OUT params is not supported. Please configure useCache=false in " + ms.getId() + " statement."); } } } } public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) { return delegate.createCacheKey(ms, parameterObject, rowBounds, boundSql); } public boolean isCached(MappedStatement ms, CacheKey key) { return delegate.isCached(ms, key); } public void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType) { delegate.deferLoad(ms, resultObject, property, key, targetType); } public void clearLocalCache() { delegate.clearLocalCache(); } private void flushCacheIfRequired(MappedStatement ms) { Cache cache = ms.getCache(); if (cache != null && ms.isFlushCacheRequired()) { tcm.clear(cache); } } @Override public void setExecutorWrapper(Executor executor) { throw new UnsupportedOperationException("This method should not be called"); } }
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