Mybatis中SqlSession下的四大对象之执行器（executor）

package org.apache.ibatis.session.defaults;
public class DefaultSqlSession implements SqlSession {
 private Configuration configuration;
 private Executor executor;
 private boolean autoCommit;
 private boolean dirty;
.......
@Override
 public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
  try {
   MappedStatement ms = configuration.getMappedStatement(statement);
   return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
  } catch (Exception e) {
   throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
  } finally {
   ErrorContext.instance().reset();
  }
 }
......
}

<bean id="sqlSessionTemplateBatch" class="org.mybatis.spring.SqlSessionTemplate">   
<constructor-arg index="0" ref="sqlSessionFactory" /> 
<!--更新采用批量的executor --> 
<constructor-arg index="1" value="BATCH"/> 
</bean> 

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
  executorType = executorType == null ? defaultExecutorType : executorType;
  executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
  Executor executor;
  if (ExecutorType.BATCH == executorType) {
   executor = new BatchExecutor(this, transaction);
  } else if (ExecutorType.REUSE == executorType) {
   executor = new ReuseExecutor(this, transaction);
  } else {
   executor = new SimpleExecutor(this, transaction);
  }
  if (cacheEnabled) {
   executor = new CachingExecutor(executor);
  }
  executor = (Executor) interceptorChain.pluginAll(executor);
  return executor;
 }

public Object pluginAll(Object target) {
  for (Interceptor interceptor : interceptors) {
   target = interceptor.plugin(target);
  }
  return target;
 }

public class Plugin implements InvocationHandler {
 private Object target;
 private Interceptor interceptor;
 private Map<Class<?>, Set<Method>> signatureMap;
 private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) {
  this.target = target;
  this.interceptor = interceptor;
  this.signatureMap = signatureMap;
 }
 public static Object wrap(Object target, Interceptor interceptor) {
  Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
  Class<?> type = target.getClass();
  Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
  if (interfaces.length > 0) {
   return Proxy.newProxyInstance(
     type.getClassLoader(),
     interfaces,
     new Plugin(target, interceptor, signatureMap));
  }
  return target;
 }
 @Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  try {
   Set<Method> methods = signatureMap.get(method.getDeclaringClass());
   if (methods != null && methods.contains(method)) {
    return interceptor.intercept(new Invocation(target, method, args));
   }
   return method.invoke(target, args);
  } catch (Exception e) {
   throw ExceptionUtil.unwrapThrowable(e);
  }
 }
 ......
}

public class SimpleExecutor extends BaseExecutor {
......
 @Override
 public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
  Statement stmt = null;
  try {
   Configuration configuration = ms.getConfiguration();
   StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
   stmt = prepareStatement(handler, ms.getStatementLog());
   return handler.<E>query(stmt, resultHandler);
  } finally {
   closeStatement(stmt);
  }
 }
 ......
 private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
  Statement stmt;
  Connection connection = getConnection(statementLog);
  stmt = handler.prepare(connection);
  handler.parameterize(stmt);
  return stmt;
 }
}