Mybatis中 SIMPLE、REUSE、BATCH的区别
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Mybatis中 SIMPLE、REUSE、BATCH的区别
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Executor分成兩大類，一類是CacheExecutor，另一類是普通Executor。
普通類又分為：
ExecutorType.SIMPLE: 這個執行器類型不做特殊的事情。它為每個語句的執行創建一個新的預處理語句。（默認）
ExecutorType.REUSE: 這個執行器類型會復用預處理語句。
ExecutorType.BATCH: 這個執行器會批量執行所有更新語句,如果 SELECT 在它們中間執行還會標定它們是 必須的,來保證一個簡單并易于理解的行為。
分別對應SimpleExecutor，ReuseExecutor，BatchExecutor，他們都繼承于BaseExecutor，BatchExecutor專門用于執行批量sql操作，ReuseExecutor會重用statement執行sql操作，SimpleExecutor只是簡單執行sql沒有什么特別的。
作用范圍：Executor的這些特點，都嚴格限制在SqlSession生命周期范圍內。
Mybatis中如何指定使用哪一種Executor執行器？
在Mybatis配置文件中，可以指定默認的ExecutorType執行器類型，也可以手動給DefaultSqlSessionFactory的創建SqlSession的方法傳遞ExecutorType類型參數。
CacheExecutor有一個重要屬性delegate，它保存的是某類普通的Executor，值在構照時傳入。執行數據庫update操作時，它直接調用delegate的update方法，執行query方法時先嘗試從cache中取值，取不到再調用delegate的查詢方法，并將查詢結果存入cache中。代碼如下：
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);
}
}
//是否關閉了executor
public boolean isClosed() {
return delegate.isClosed();
}
public int update(MappedStatement ms, Object parameterObject) throws SQLException {
flushCacheIfRequired(ms);//是否需要更緩存
return delegate.update(ms, parameterObject);//更新數據
}
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);//獲取記錄
}
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
throws SQLException {
Cache cache = ms.getCache();//獲取緩存
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);//從緩存中獲取數據 //如果為空，則查詢數據庫，并把結果保存到緩存中
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通過類名可以看出，它是一個簡單的執行類，并不會做一些處理就執行sql。（每執行一次update或select，就開啟一個Statement對象，用完立刻關閉Statement對象）源碼及分析如下：
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();//獲得配置 //獲得statementHandler里面有statement，來處理
StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.update(stmt);//最終是一個statement進行處理
} 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);//將Statement轉為PrepareStatement
return stmt;
}
}
BatchExecutor :通過批量操作來提高性能。（執行update（沒有select，JDBC批處理不支持select），將所有sql都添加到批處理中（addBatch()），等待統一執行（executeBatch()），它緩存了多個Statement對象，每個Statement對象都是addBatch()完畢后，等待逐一執行executeBatch()批處理。與JDBC批處理相同。）
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();//獲得配置信息
final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
final BoundSql boundSql = handler.getBoundSql();
final String sql = boundSql.getSql();//獲得Sql語句
final Statement stmt; //如果sql語句等于當前sql MappedStatement 等于當前Map碰到Statement
if (sql.equals(currentSql) && ms.equals(currentStatement)) {
int last = statementList.size() - 1;
stmt = statementList.get(last);//獲得最后一個 //有相同的MappedStatement和參數
BatchResult batchResult = batchResultList.get(last);
batchResult.addParameterObject(parameterObject);
} else { //如果不存在就創建一個批處理操作
Connection connection = getConnection(ms.getStatementLog());
stmt = handler.prepare(connection);
currentSql = sql;
currentStatement = ms;
statementList.add(stmt);//添加批量處理操作
batchResultList.add(new BatchResult(ms, sql, parameterObject));
}
handler.parameterize(stmt);
handler.batch(stmt);//最終是調用jdbc的批處理操作
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，記錄執行次數
public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {
try {
List<BatchResult> results = new ArrayList<BatchResult>();
if (isRollback) {
return Collections.emptyList();
} else { //如果進行了批量處理
for (int i = 0, n = statementList.size(); i < n; i++) {
Statement stmt = statementList.get(i);
BatchResult batchResult = batchResultList.get(i);
try { //記錄批量處理執行操作的條數
batchResult.setUpdateCounts(stmt.executeBatch());
MappedStatement ms = batchResult.getMappedStatement();
List<Object> parameterObjects = batchResult.getParameterObjects();//參數對象集合
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);//記錄操作
}
return results;
}
} finally {
for (Statement stmt : statementList) {
closeStatement(stmt);
}
currentSql = null;
statementList.clear();
batchResultList.clear();
}
}
}
ReuseExecutor: 重復使用執行，其定義了一個Map<String, Statement>，將執行的sql作為key，將執行的Statement作為value保存，這樣執行相同的sql時就可以使用已經存在的Statement，就不需要新創建了。（執行update或select，以sql作為key查找Statement對象，存在就使用，不存在就創建，用完后，不關閉Statement對象，而是放置于Map內，供下一次使用。簡言之，就是重復使用Statement對象。）源碼及分析如下：
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());//轉換為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);//關閉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();//獲得sql語句
if (hasStatementFor(sql)) { //查看是否存在Statement
stmt = getStatement(sql);//如果存在就獲取Statement
} else {
Connection connection = getConnection(statementLog);
stmt = handler.prepare(connection);//否則通過連接創建一個Statement
putStatement(sql, stmt);//將sql語句及對應的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語句對應的Statement
return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed();
} catch (SQLException e) {
return false;
}
}
//獲得Sql語句對應的Statement
private Statement getStatement(String s) {
return statementMap.get(s);
}
//將sql語句及對應的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
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