mybatis四大介面之 Executor

阿新 • • 發佈：2018-12-04

【參考文章】：Mybatis-Executor解析

1. Executor的繼承結構

2. Executor（頂層介面）

　　定義了執行器的一些基本操作；

public interface Executor {

  ResultHandler NO_RESULT_HANDLER = null;
  // 更新
  int update(MappedStatement ms, Object parameter) throws SQLException;
  // 查詢，先查快取，再查資料庫
  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey cacheKey, BoundSql boundSql) throws 
 SQLException;
  // 查詢
  <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;

  <E> Cursor<E> queryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds) throws SQLException;

  List<BatchResult> flushStatements() throws 
 SQLException;
  // 事務提交
  void commit(boolean required) throws SQLException;
  // 事務回滾
  void rollback(boolean required) throws SQLException;
  // 建立快取的鍵物件
  CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql);
  // 快取中是否有這個查詢的結果
  boolean isCached(MappedStatement ms, CacheKey key);
   
// 清空快取
  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);

}

3. BaseExecutor

　　BaseExecutor是一個抽象類，採用模板方法的設計模式。

　　它實現了Executor介面，實現了執行器的基本功能。

　　具體使用哪一個Executor則是可以在 mybatis 的 config.xml 中進行配置的。預設為SimpleExecutor；

　　配置如下：

<settings>
    <!--SIMPLE、REUSE、BATCH-->
    <setting name="defaultExecutorType" value="SIMPLE"/>
</settings>

3.1 構造方法

　　子類的構造方法會呼叫 BaseExecutor 的構造方法。

　　預設都支援一級快取；

public abstract class BaseExecutor implements Executor {
        
  protected BaseExecutor(Configuration configuration, Transaction transaction) {
    this.transaction = transaction;
    this.deferredLoads = new ConcurrentLinkedQueue<DeferredLoad>();
    // 一級快取
    this.localCache = new PerpetualCache("LocalCache");
    this.localOutputParameterCache = new PerpetualCache("LocalOutputParameterCache");
    this.closed = false;
    this.configuration = configuration;
    this.wrapper = this;
  }
}

3.2 update

　　insert，update，delete操作都會呼叫此方法；

　　呼叫此方法時會清空一級快取；

   @Override
  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.");
    }
    // 資料變更操作會清空一級快取
    clearLocalCache();
    return doUpdate(ms, parameter);
  }

3.3 query

　　查詢操作會先在快取中查詢，快取命中失敗後再去資料中查詢

  @Override
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
    BoundSql boundSql = ms.getBoundSql(parameter);
    // 建立一級快取的鍵物件
    CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
            // 呼叫下面的 query 方法
    return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
 }

  @SuppressWarnings("unchecked")
  @Override
  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());
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    if (queryStack == 0 && ms.isFlushCacheRequired()) {
      clearLocalCache();
    }
    List<E> list;
    try {
      queryStack++;
      // 先在快取中查詢，快取命中失敗再去資料庫查詢
      list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
      if (list != null) {
        handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
      } else {
        list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
      }
    } finally {
      queryStack--;
    }
    if (queryStack == 0) {
      for (DeferredLoad deferredLoad : deferredLoads) {
        deferredLoad.load();
      }
      // issue #601
      deferredLoads.clear();
      if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
        // issue #482
        clearLocalCache();
      }
    }
    return list;
  }

3.4 createCacheKey

　　一級快取通過 HashMap 實現，它的鍵物件根據SQL的ID，引數，SQL本身，分頁引數以及JDBC的引數資訊構成。

  @Override
  // 建立CacheKey物件
  public CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql) {
    if (closed) {
      throw new ExecutorException("Executor was closed.");
    }
    CacheKey cacheKey = new CacheKey();
    // MappedStatement的id
    cacheKey.update(ms.getId());
    // 分頁引數的offset
    cacheKey.update(rowBounds.getOffset());
    // 分頁引數的limit
    cacheKey.update(rowBounds.getLimit());
    // SQL語句本身
    cacheKey.update(boundSql.getSql());
    // 傳遞給jdbc的引數
    List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
    TypeHandlerRegistry typeHandlerRegistry = ms.getConfiguration().getTypeHandlerRegistry();
    // mimic DefaultParameterHandler logic
    for (ParameterMapping parameterMapping : parameterMappings) {
      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);
      }
    }
    if (configuration.getEnvironment() != null) {
      // issue #176
      cacheKey.update(configuration.getEnvironment().getId());
    }
    return cacheKey;
  }

3.5定義的抽象方法

  // 定義的四個抽象方法，在去掉 do 字首的相應方法中被呼叫
  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 abstract <E> Cursor<E> doQueryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds, BoundSql boundSql)
      throws SQLException;

4. SimpleExecutor

　　最簡單的執行器，根據對應的sql直接執行即可，不會做一些額外的操作；

　　拼接完SQL之後，直接交給 StatementHandler 去執行。

/**
 *    Copyright 2009-2016 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor;

import org.apache.ibatis.cursor.Cursor;
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;

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

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

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

  @Override
  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.update(stmt);
    } finally {
      closeStatement(stmt);
    }
  }

  @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);
    }
  }

  @Override
  protected <E> Cursor<E> doQueryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds, BoundSql boundSql) throws SQLException {
    Configuration configuration = ms.getConfiguration();
    StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, null, boundSql);
    Statement stmt = prepareStatement(handler, ms.getStatementLog());
    return handler.<E>queryCursor(stmt);
  }

  @Override
  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, transaction.getTimeout());
    handler.parameterize(stmt);
    return stmt;
  }

}

View Code

5. BatchExecutor

　　通過批量操作來優化效能。通常需要注意的是批量更新操作，由於內部有快取的實現，使用完成後記得呼叫flushStatements來清除快取。

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>();
  private final List<BatchResult> batchResultList = new ArrayList<BatchResult>();
  // 上一次的SQL語句
  private String currentSql;
  // 上一次的MappedStatement 物件
  private MappedStatement currentStatement;

  // 因為呼叫父類的構造方法，所以 BatchExecutor 自己的私有屬性 currentSql和currentStatement 開始都為null
  public BatchExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  @Override
  public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {
    final Configuration configuration = ms.getConfiguration();
    final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
    final BoundSql boundSql = handler.getBoundSql();
    final String sql = boundSql.getSql();
    final Statement stmt;
    // 第一次肯定是false，進入else分支，currentSql和currentStatement被初始化，後面進入false分支則進行更新
    if (sql.equals(currentSql) && ms.equals(currentStatement)) {
        // 取上一次的 Statement 物件
      int last = statementList.size() - 1;
      stmt = statementList.get(last);
      applyTransactionTimeout(stmt);
     handler.parameterize(stmt);//fix Issues 322
      BatchResult batchResult = batchResultList.get(last);
      batchResult.addParameterObject(parameterObject);
    } else {
      Connection connection = getConnection(ms.getStatementLog());
      stmt = handler.prepare(connection, transaction.getTimeout());
      handler.parameterize(stmt);    //fix Issues 322
      // currentSql和currentStatement 更新為此次的物件
      currentSql = sql;
      currentStatement = ms;
      statementList.add(stmt);
      batchResultList.add(new BatchResult(ms, sql, parameterObject));
    }
  // handler.parameterize(stmt);
    handler.batch(stmt);
    return BATCH_UPDATE_RETURN_VALUE;
  }
  
}

6. ReuseExecutor

　　可重用的執行器，重用的物件是Statement，也就是說該執行器會快取同一個sql的Statement，省去Statement的重新建立，優化效能。　　內部的實現是通過一個HashMap來維護Statement物件的。由於當前Map只在該session中有效，所以使用完成後記得呼叫 flushStatements來清除Map。　　呼叫實現的四個抽象方法時會呼叫 prepareStatement()

public class ReuseExecutor extends BaseExecutor {


  private final Map<String, Statement> statementMap = new HashMap<String, Statement>();
  
  // 呼叫父類構造器
  public ReuseExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  
  private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    BoundSql boundSql = handler.getBoundSql();
    String sql = boundSql.getSql();
    if (hasStatementFor(sql)) {
        // 如果快取了該SQL，則返回其Statement物件
      stmt = getStatement(sql);
      applyTransactionTimeout(stmt);
    } else {
        // 如果沒有快取該SQL，則建立SQL的Statement，並加入快取
      Connection connection = getConnection(statementLog);
      stmt = handler.prepare(connection, transaction.getTimeout());
      putStatement(sql, stmt);
    }
    handler.parameterize(stmt);
    return stmt;
  }

  // 是否快取了這個 sql
  private boolean hasStatementFor(String sql) {
    try {
      return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed();
    } catch (SQLException e) {
      return false;
    }
  }
  
  // 返回指定sql的 Statement
  private Statement getStatement(String s) {
    return statementMap.get(s);
  }

  // 新增SQL和Statement
  private void putStatement(String sql, Statement stmt) {
    statementMap.put(sql, stmt);
  }

}

7. CachingExecutor

　　啟用於二級快取時的執行器；　　採用靜態代理；代理一個 Executor 物件。　　執行 update 方法前判斷是否清空二級快取；　　執行 query 方法前先在二級快取中查詢，命中失敗再通過被代理類查詢。　　

public class CachingExecutor implements Executor {
    // 持有的 Executor，最終的操作都由該物件實現
    private final Executor delegate;
    private final TransactionalCacheManager tcm = new TransactionalCacheManager();

    public CachingExecutor(Executor delegate) {
        this.delegate = delegate;
        delegate.setExecutorWrapper(this);
    }
    
    public int update(MappedStatement ms, Object parameterObject) throws SQLException {
        this.flushCacheIfRequired(ms);
        return this.delegate.update(ms, parameterObject);
    }
    
    public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
        Cache cache = ms.getCache();
        if (cache != null) {
            this.flushCacheIfRequired(ms);
            if (ms.isUseCache() && resultHandler == null) {
                this.ensureNoOutParams(ms, boundSql);
                List<E> list = (List)this.tcm.getObject(cache, key);
                if (list == null) {
                    list = this.delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
                    this.tcm.putObject(cache, key, list);
                }

                return list;
            }
        }

        return this.delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }
        // 是否清空二級快取
        private void flushCacheIfRequired(MappedStatement ms) {
        Cache cache = ms.getCache();
        if (cache != null && ms.isFlushCacheRequired()) {
            this.tcm.clear(cache);
        }

    }
}

mybatis四大介面之 Executor

【參考文章】：Mybatis-Executor解析

1. Executor的繼承結構

2. Executor（頂層介面）

3. BaseExecutor

3.1 構造方法

3.2 update

3.3 query

3.4 createCacheKey

3.5定義的抽象方法

4. SimpleExecutor

5. BatchExecutor

6. ReuseExecutor

7. CachingExecutor

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mybatis四大介面之 Executor

【參考文章】：Mybatis-Executor解析

1. Executor的繼承結構

2. Executor（頂層介面）

3. BaseExecutor

3.1 構造方法

3.2 update

3.3 query

3.4 createCacheKey

3.5定義的抽象方法

4. SimpleExecutor

5. BatchExecutor

6. ReuseExecutor

7. CachingExecutor

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