MyBatis框架的使用及源码分析(十) CacheExecutor,SimpleExecutor,BatchExecutor ,ReuseExecutor

Executor分成两大类,一类是CacheExecutor,另一类是普通Executor。

普通类又分为: 

ExecutorType.SIMPLE: 这个执行器类型不做特殊的事情。它为每个语句的执行创建一个新的预处理语句。
ExecutorType.REUSE: 这个执行器类型会复用预处理语句。
ExecutorType.BATCH: 这个执行器会批量执行所有更新语句,如果 SELECT 在它们中间执行还会标定它们是 必须的,来保证一个简单并易于理解的行为。

分别对应SimpleExecutor,ReuseExecutor,BatchExecutor,他们都继承于BaseExecutor,BatchExecutor专门用于执行批量sql操作,ReuseExecutor会重用statement执行sql操作,SimpleExecutor只是简单执行sql没有什么特别的。

 

CacheExecutor有一个重要属性delegate,它保存的是某类普通的Executor,值在构照时传入。执行数据库update操作时,它直接调用delegate的update方法,执行query方法时先尝试从cache中取值,取不到再调用delegate的查询方法,并将查询结果存入cache中。代码如下:

package org.apache.ibatis.executor;

import java.sql.SQLException;
import java.util.List;

import org.apache.ibatis.cache.Cache;
import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.cache.TransactionalCacheManager;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.ParameterMode;
import org.apache.ibatis.mapping.StatementType;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

/**
 * @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 { flushCacheIfRequired(ms);//是否需要更缓存  return delegate.update(ms, parameterObject);//更新数据  } public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { BoundSql boundSql = ms.getBoundSql(parameterObject); CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql); return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);//获取记录 } public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { Cache cache = ms.getCache();//获取缓存 if (cache != null) { flushCacheIfRequired(ms); if (ms.isUseCache() && resultHandler == null) { ensureNoOutParams(ms, parameterObject, boundSql); @SuppressWarnings("unchecked") List<E> list = (List<E>) tcm.getObject(cache, key);//从缓存中获取数据 
//如果为空,则查询数据库,并把结果保存到缓存中
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"); } }

 

SimpleExecutor通过类名可以看出,它是一个简单的执行类,并不会做一些处理就执行sql,源码及分析如下:

package org.apache.ibatis.executor;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Collections;
import java.util.List;

import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

/**
 * @author Clinton Begin
 */
public class SimpleExecutor extends BaseExecutor {

  public SimpleExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();//获得配置
//获得statementHandler里面有statement,来处理  StatementHandler handler
= configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null); stmt = prepareStatement(handler, ms.getStatementLog()); return handler.update(stmt);//最终是一个statement进行处理  } finally { closeStatement(stmt); } } 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); } } public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException { return Collections.emptyList(); } private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Statement stmt; Connection connection = getConnection(statementLog); stmt = handler.prepare(connection); handler.parameterize(stmt);//将Statement转为PrepareStatement  return stmt; } }

 

BatchExecutor : 通过批量操作来提高性能

package org.apache.ibatis.executor;

import java.sql.BatchUpdateException;
import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.ibatis.executor.keygen.Jdbc3KeyGenerator;
import org.apache.ibatis.executor.keygen.KeyGenerator;
import org.apache.ibatis.executor.keygen.NoKeyGenerator;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

/**
 * @author Jeff Butler 
 */
public class BatchExecutor extends BaseExecutor {

  public static final int BATCH_UPDATE_RETURN_VALUE = Integer.MIN_VALUE + 1002;

  private final List<Statement> statementList = new ArrayList<Statement>();//Statement list
  private final List<BatchResult> batchResultList = new ArrayList<BatchResult>();//batch list
  private String currentSql;
  private MappedStatement currentStatement;

  public BatchExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {
    final Configuration configuration = ms.getConfiguration();//获得配置信息
    final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
    final BoundSql boundSql = handler.getBoundSql();
    final String sql = boundSql.getSql();//获得Sql语句
    final Statement stmt;
//如果sql语句等于当前sql MappedStatement 等于当前Map碰到Statement  
if (sql.equals(currentSql) && ms.equals(currentStatement)) { int last = statementList.size() - 1; stmt = statementList.get(last);//获得最后一个
//有相同的MappedStatement和参数 BatchResult batchResult
= batchResultList.get(last); batchResult.addParameterObject(parameterObject); } else {
//如果不存在就创建一个批处理操作  Connection connection
= getConnection(ms.getStatementLog()); stmt = handler.prepare(connection); currentSql = sql; currentStatement = ms; statementList.add(stmt);//添加批量处理操作 batchResultList.add(new BatchResult(ms, sql, parameterObject)); } handler.parameterize(stmt); handler.batch(stmt);//最终是调用jdbc的批处理操作  return BATCH_UPDATE_RETURN_VALUE; } public <E> List<E> doQuery(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { Statement stmt = null; try { flushStatements(); Configuration configuration = ms.getConfiguration(); StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameterObject, rowBounds, resultHandler, boundSql); Connection connection = getConnection(ms.getStatementLog()); stmt = handler.prepare(connection); handler.parameterize(stmt); return handler.<E>query(stmt, resultHandler); } finally { closeStatement(stmt); } }
//刷新Statement,记录执行次数
public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException { try { List<BatchResult> results = new ArrayList<BatchResult>(); if (isRollback) { return Collections.emptyList(); } else {
//如果进行了批量处理
for (int i = 0, n = statementList.size(); i < n; i++) { Statement stmt = statementList.get(i); BatchResult batchResult = batchResultList.get(i); try {
//记录批量处理执行操作的条数 batchResult.setUpdateCounts(stmt.executeBatch()); MappedStatement ms
= batchResult.getMappedStatement(); List<Object> parameterObjects = batchResult.getParameterObjects();//参数对象集合 KeyGenerator keyGenerator = ms.getKeyGenerator();//生成key  if (Jdbc3KeyGenerator.class.equals(keyGenerator.getClass())) { Jdbc3KeyGenerator jdbc3KeyGenerator = (Jdbc3KeyGenerator) keyGenerator; jdbc3KeyGenerator.processBatch(ms, stmt, parameterObjects); } else if (!NoKeyGenerator.class.equals(keyGenerator.getClass())) { //issue #141 for (Object parameter : parameterObjects) { keyGenerator.processAfter(this, ms, stmt, parameter); } } } catch (BatchUpdateException e) { StringBuffer message = new StringBuffer(); message.append(batchResult.getMappedStatement().getId()) .append(" (batch index #") .append(i + 1) .append(")") .append(" failed."); if (i > 0) { message.append(" ") .append(i) .append(" prior sub executor(s) completed successfully, but will be rolled back."); } throw new BatchExecutorException(message.toString(), e, results, batchResult); } results.add(batchResult);//记录操作  } return results; } } finally { for (Statement stmt : statementList) { closeStatement(stmt); } currentSql = null; statementList.clear(); batchResultList.clear(); } } }

 

ReuseExecutor: 重复使用执行,其定义了一个Map<String, Statement>,将执行的sql作为key,将执行的Statement作为value保存,这样执行相同的sql时就可以使用已经存在的Statement,就不需要新创建了,源码及分析如下:

package org.apache.ibatis.executor;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

/**
 * @author Clinton Begin
 */
public class ReuseExecutor extends BaseExecutor {

  private final Map<String, Statement> statementMap = new HashMap<String, Statement>();

  public ReuseExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Configuration configuration = ms.getConfiguration();
    StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
    Statement stmt = prepareStatement(handler, ms.getStatementLog());//转换为PrepareStatement 
    return handler.update(stmt);
  }

  public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    Configuration configuration = ms.getConfiguration();
    StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
    Statement stmt = prepareStatement(handler, ms.getStatementLog());
    return handler.<E>query(stmt, resultHandler);
  }

  public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {
    for (Statement stmt : statementMap.values()) {
      closeStatement(stmt);//关闭Statement
    }
    statementMap.clear();//清空sql
    return Collections.emptyList();
  }

  private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    BoundSql boundSql = handler.getBoundSql();
    String sql = boundSql.getSql();//获得sql语句
    if (hasStatementFor(sql)) {  //查看是否存在Statement  
      stmt = getStatement(sql);//如果存在就获取Statement  
    } else {
      Connection connection = getConnection(statementLog);
      stmt = handler.prepare(connection);//否则通过连接创建一个Statement 
      putStatement(sql, stmt);//将sql语句及对应的Statement 保存到map中
    }
    handler.parameterize(stmt);
    return stmt;
  }

  private boolean hasStatementFor(String sql) {
    try {
//查看map中是否含有sql语句对应的Statement  
return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed(); } catch (SQLException e) { return false; } }
//获得Sql语句对应的Statement 
private Statement getStatement(String s) { return statementMap.get(s); }
//将sql语句及对应的Statement保存到map中
private void putStatement(String sql, Statement stmt) { statementMap.put(sql, stmt); } }

 

posted @ 2017-09-21 00:20  猪脚踏浪  阅读(...)  评论(...编辑  收藏