Mybatis中 SIMPLE、REUSE、BATCH的区别

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。（默认）
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。

作用范围：Executor的这些特点，都严格限制在SqlSession生命周期范围内。

Mybatis中如何指定使用哪一种Executor执行器？

在Mybatis配置文件中，可以指定默认的ExecutorType执行器类型，也可以手动给DefaultSqlSessionFactory的创建SqlSession的方法传递ExecutorType类型参数。

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。（每执行一次update或select，就开启一个Statement对象，用完立刻关闭Statement对象）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。（执行update（没有select，JDBC批处理不支持select），将所有sql都添加到批处理中（addBatch()），等待统一执行（executeBatch()），它缓存了多个Statement对象，每个Statement对象都是addBatch()完毕后，等待逐一执行executeBatch()批处理。与JDBC批处理相同。）

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。（执行update或select，以sql作为key查找Statement对象，存在就使用，不存在就创建，用完后，不关闭Statement对象，而是放置于Map内，供下一次使用。简言之，就是重复使用Statement对象。）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);
  }

}

　　https://www.cnblogs.com/zsg88/p/7566039.html

Mybatis中 SIMPLE、REUSE、BATCH的区别

Informix存储过程

如何使用 Dump 文件？

最新文章

聚氯乙烯加工的主要用途是什么

阿里斯顿燃气壁挂炉好不好？阿里斯顿壁挂炉产品系列推荐

如何选购925银吊坠

中华人才网招聘（找工作哪个网站最真实）

公开选拔（公开选拔不拘一格降人才）

Fmea软件(具体怎么做fmea)

北京八中少儿班(北京八中少儿班2021)

消息称三星电子将从天马微电子采购OLED显示屏用于智能手机

以科技创新赋能高教职教新质人才培养华为擎云亮相第62届中国高等教育博览会

全新智己LS6、智己L6亮相广州车展首次推出“灵蜥掉头”与“云台车身”功能

标签

热评文章

十大led节能灯品牌排名

Kans化妆品怎么样(Kans属于什么档次)

桌球技巧教学

八字轻松入门（八字命理入门基础知识）

三个龙念什么(三个马念什么)

Mybatis中 SIMPLE、REUSE、BATCH的区别

Informix存储过程

如何使用 Dump 文件？

最新文章

聚氯乙烯加工的主要用途是什么

标签

热评文章

十大led节能灯品牌排名

Kans化妆品怎么样(Kans属于什么档次)

桌球技巧教学

八字轻松入门（八字命理入门基础知识）

三个龙念什么(三个马念什么)

关注我们的公众号