這篇文章主要講解了“MyBatis的事務(wù)管理方式”，文中的講解內(nèi)容簡(jiǎn)單清晰，易于學(xué)習(xí)與理解，下面請(qǐng)大家跟著小編的思路慢慢深入，一起來研究和學(xué)習(xí)“MyBatis的事務(wù)管理方式”吧！
1. 運(yùn)行環(huán)境 Enviroment
當(dāng) MyBatis 與不同的應(yīng)用結(jié)合時(shí)，需要不同的事務(wù)管理機(jī)制。與 Spring 結(jié)合時(shí)，由 Spring 來管理事務(wù)；單獨(dú)使用時(shí)需要自行管理事務(wù)，在容器里運(yùn)行時(shí)可能由容器進(jìn)行管理。
MyBatis 用 Enviroment 來表示運(yùn)行環(huán)境，其封裝了三個(gè)屬性：
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public class Configuration {
// 一個(gè) MyBatis 的配置只對(duì)應(yīng)一個(gè)環(huán)境
protected Environment environment;
// 其他屬性 .....
}
public final class Environment {
private final String id;
private final TransactionFactory transactionFactory;
private final DataSource dataSource;
}2. 事務(wù)抽象
MyBatis 把事務(wù)管理抽象出 Transaction 接口，由 TransactionFactory 接口的實(shí)現(xiàn)類負(fù)責(zé)創(chuàng)建。
public interface Transaction {
Connection getConnection() throws SQLException;
void commit() throws SQLException;
void rollback() throws SQLException;
void close() throws SQLException;
Integer getTimeout() throws SQLException;
}
public interface TransactionFactory {
void setProperties(Properties props);
Transaction newTransaction(Connection conn);
Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);
}Executor 的實(shí)現(xiàn)持有一個(gè) SqlSession 實(shí)現(xiàn)，事務(wù)控制是委托給 SqlSession 的方法來實(shí)現(xiàn)的。
public abstract class BaseExecutor implements Executor {
protected Transaction transaction;
public void commit(boolean required) throws SQLException {
if (closed) {
throw new ExecutorException("Cannot commit, transaction is already closed");
}
clearLocalCache();
flushStatements();
if (required) {
transaction.commit();
}
}
public void rollback(boolean required) throws SQLException {
if (!closed) {
try {
clearLocalCache();
flushStatements(true);
} finally {
if (required) {
transaction.rollback();
}
}
}
}
// 省略其他方法、屬性
}3. 與 Spring 集成的事務(wù)管理
3.1 配置 TransactionFactory
與 Spring 集成時(shí)，通過 SqlSessionFactoryBean 來初始化 MyBatis 。
protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
Configuration configuration;
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configuration != null) {
configuration = this.configuration;
if (configuration.getVariables() == null) {
configuration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {
configuration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
configuration = xmlConfigBuilder.getConfiguration();
} else {
configuration = new Configuration();
configuration.setVariables(this.configurationProperties);
}
if (this.objectFactory != null) {
configuration.setObjectFactory(this.objectFactory);
}
if (this.objectWrapperFactory != null) {
configuration.setObjectWrapperFactory(this.objectWrapperFactory);
}
if (this.vfs != null) {
configuration.setVfsImpl(this.vfs);
}
if (hasLength(this.typeAliasesPackage)) {
String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeAliasPackageArray) {
configuration.getTypeAliasRegistry().registerAliases(packageToScan,
typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
}
}
if (!isEmpty(this.typeAliases)) {
for (Class typeAlias : this.typeAliases) {
configuration.getTypeAliasRegistry().registerAlias(typeAlias);
}
}
if (!isEmpty(this.plugins)) {
for (Interceptor plugin : this.plugins) {
configuration.addInterceptor(plugin);
}
}
if (hasLength(this.typeHandlersPackage)) {
String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeHandlersPackageArray) {
configuration.getTypeHandlerRegistry().register(packageToScan);
}
}
if (!isEmpty(this.typeHandlers)) {
for (TypeHandler typeHandler : this.typeHandlers) {
configuration.getTypeHandlerRegistry().register(typeHandler);
}
}
if (this.databaseIdProvider != null) {//fix #64 set databaseId before parse mapper xmls
try {
configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException e) {
throw new NestedIOException("Failed getting a databaseId", e);
}
}
if (this.cache != null) {
configuration.addCache(this.cache);
}
if (xmlConfigBuilder != null) {
try {
xmlConfigBuilder.parse();
} catch (Exception ex) {
throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
} finally {
ErrorContext.instance().reset();
}
}
// 創(chuàng)建 SpringManagedTransactionFactory
if (this.transactionFactory == null) {
this.transactionFactory = new SpringManagedTransactionFactory();
}
// 封裝成 Environment
configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));
if (!isEmpty(this.mapperLocations)) {
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
configuration, mapperLocation.toString(), configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
}
} else {
}
return this.sqlSessionFactoryBuilder.build(configuration);
}public class SqlSessionFactoryBuilder {
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
}重點(diǎn)是在構(gòu)建 MyBatis Configuration 對(duì)象時(shí)，把 transactionFactory 配置成 SpringManagedTransactionFactory，再封裝成 Environment 對(duì)象。
3.2 運(yùn)行時(shí)事務(wù)管理
Mapper 的代理對(duì)象持有的是 SqlSessionTemplate，其實(shí)現(xiàn)了 SqlSession 接口。
SqlSessionTemplate 的方法并不直接調(diào)用具體的 SqlSession 的方法，而是委托給一個(gè)動(dòng)態(tài)代理，通過代理 SqlSessionInterceptor 對(duì)方法調(diào)用進(jìn)行攔截。
SqlSessionInterceptor 負(fù)責(zé)獲取真實(shí)的與數(shù)據(jù)庫(kù)關(guān)聯(lián)的 SqlSession 實(shí)現(xiàn)，并在方法執(zhí)行完后決定提交或回滾事務(wù)、關(guān)閉會(huì)話。
public class SqlSessionTemplate implements SqlSession, DisposableBean {
private final SqlSessionFactory sqlSessionFactory;
private final ExecutorType executorType;
private final SqlSession sqlSessionProxy;
private final PersistenceExceptionTranslator exceptionTranslator;
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
notNull(executorType, "Property 'executorType' is required");
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
// 因?yàn)?nbsp;SqlSession 接口聲明的方法也不少，
// 在每個(gè)方法里添加事務(wù)相關(guān)的攔截比較麻煩，
// 不如創(chuàng)建一個(gè)內(nèi)部的代理對(duì)象進(jìn)行統(tǒng)一處理。
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
}
public int update(String statement) {
// 在代理對(duì)象上執(zhí)行方法調(diào)用
return this.sqlSessionProxy.update(statement);
}
// 對(duì)方法調(diào)用進(jìn)行攔截，加入事務(wù)控制邏輯
private class SqlSessionInterceptor implements InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 獲取與數(shù)據(jù)庫(kù)關(guān)聯(lián)的會(huì)話
SqlSession sqlSession = SqlSessionUtils.getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
try {
// 執(zhí)行 SQL 操作
Object result = method.invoke(sqlSession, args);
if (!SqlSessionUtils.isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
// 如果 sqlSession 不是 Spring 管理的，則要自行提交事務(wù)
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
SqlSessionUtils.closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
SqlSessionUtils.closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}
}SqlSessionUtils 封裝了對(duì) Spring 事務(wù)管理機(jī)制的訪問。
// SqlSessionUtils
public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {
// 從 Spring 的事務(wù)管理機(jī)制那里獲取當(dāng)前事務(wù)關(guān)聯(lián)的會(huì)話
SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
SqlSession session = sessionHolder(executorType, holder);
if (session != null) {
// 已經(jīng)有一個(gè)會(huì)話則復(fù)用
return session;
}
// 創(chuàng)建新的 會(huì)話
session = sessionFactory.openSession(executorType);
// 注冊(cè)到 Spring 的事務(wù)管理機(jī)制里
registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);
return session;
}
private static void registerSessionHolder(SqlSessionFactory sessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator, SqlSession session) {
SqlSessionHolder holder;
if (TransactionSynchronizationManager.isSynchronizationActive()) {
Environment environment = sessionFactory.getConfiguration().getEnvironment();
if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) {
holder = new SqlSessionHolder(session, executorType, exceptionTranslator);
TransactionSynchronizationManager.bindResource(sessionFactory, holder);
// 重點(diǎn)：注冊(cè)會(huì)話管理的回調(diào)鉤子，真正的關(guān)閉動(dòng)作是在回調(diào)里完成的。
TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));
holder.setSynchronizedWithTransaction(true);
// 維護(hù)會(huì)話的引用計(jì)數(shù)
holder.requested();
} else {
if (TransactionSynchronizationManager.getResource(environment.getDataSource()) == null) {
} else {
throw new TransientDataAccessResourceException(
"SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization");
}
}
} else {
}
}
public static void closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory) {
// 從線程本地變量里獲取 Spring 管理的會(huì)話
SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
if ((holder != null) && (holder.getSqlSession() == session)) {
// Spring 管理的不直接關(guān)閉，由回調(diào)鉤子來關(guān)閉
holder.released();
} else {
// 非 Spring 管理的直接關(guān)閉
session.close();
}
}SqlSessionSynchronization 是 SqlSessionUtils 的內(nèi)部私有類，用于作為回調(diào)鉤子與 Spring 的事務(wù)管理機(jī)制協(xié)調(diào)工作，TransactionSynchronizationManager 在適當(dāng)?shù)臅r(shí)候回調(diào)其方法。
private static final class SqlSessionSynchronization extends TransactionSynchronizationAdapter {
private final SqlSessionHolder holder;
private final SqlSessionFactory sessionFactory;
private boolean holderActive = true;
public SqlSessionSynchronization(SqlSessionHolder holder, SqlSessionFactory sessionFactory) {
this.holder = holder;
this.sessionFactory = sessionFactory;
}
public int getOrder() {
return DataSourceUtils.CONNECTION_SYNCHRONIZATION_ORDER - 1;
}
public void suspend() {
if (this.holderActive) {
TransactionSynchronizationManager.unbindResource(this.sessionFactory);
}
}
public void resume() {
if (this.holderActive) {
TransactionSynchronizationManager.bindResource(this.sessionFactory, this.holder);
}
}
public void beforeCommit(boolean readOnly) {
if (TransactionSynchronizationManager.isActualTransactionActive()) {
try {
this.holder.getSqlSession().commit();
} catch (PersistenceException p) {
if (this.holder.getPersistenceExceptionTranslator() != null) {
DataAccessException translated = this.holder
.getPersistenceExceptionTranslator()
.translateExceptionIfPossible(p);
if (translated != null) {
throw translated;
}
}
throw p;
}
}
}
public void beforeCompletion() {
if (!this.holder.isOpen()) {
TransactionSynchronizationManager.unbindResource(sessionFactory);
this.holderActive = false;
// 真正關(guān)閉數(shù)據(jù)庫(kù)會(huì)話
this.holder.getSqlSession().close();
}
}
public void afterCompletion(int status) {
if (this.holderActive) {
TransactionSynchronizationManager.unbindResourceIfPossible(sessionFactory);
this.holderActive = false;
// 真正關(guān)閉數(shù)據(jù)庫(kù)會(huì)話
this.holder.getSqlSession().close();
}
this.holder.reset();
}
}3.3 創(chuàng)建新會(huì)話
// DefaultSqlSessionFactory
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
// 獲取事務(wù)工廠實(shí)現(xiàn)
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
final Executor executor = configuration.newExecutor(tx, execType);
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
if (environment == null || environment.getTransactionFactory() == null) {
return new ManagedTransactionFactory();
}
return environment.getTransactionFactory();
}4. 小結(jié)
MyBatis 的核心組件 Executor 通過 Transaction 接口來進(jìn)行事務(wù)控制。
與 Spring 集成時(shí)，初始化 Configuration 時(shí)會(huì)把 transactionFactory 設(shè)置為 SpringManagedTransactionFactory 的實(shí)例。
每個(gè) Mapper 代理里注入的 SqlSession 是 SqlSessionTemplate 的實(shí)例，其實(shí)現(xiàn)了 SqlSession 接口；
SqlSessionTemplate 把對(duì) SqlSession 接口里聲明的方法調(diào)用委托給內(nèi)部的一個(gè)動(dòng)態(tài)代理，該代理的方法處理器為內(nèi)部類 SqlSessionInterceptor 。
SqlSessionInterceptor 接收到方法調(diào)用時(shí)，通過 SqlSessionUtil 訪問 Spring 的事務(wù)設(shè)施，如果有與 Spring 當(dāng)前事務(wù)關(guān)聯(lián)的 SqlSession 則復(fù)用；沒有則創(chuàng)建一個(gè)。
SqlSessionInterceptor 根據(jù) Spring 當(dāng)前事務(wù)的狀態(tài)來決定是否提交或回滾事務(wù)。會(huì)話的真正關(guān)閉是通過注冊(cè)在 TransactionSynchronizationManager 上的回調(diào)鉤子實(shí)現(xiàn)的。
感謝各位的閱讀，以上就是“MyBatis的事務(wù)管理方式”的內(nèi)容了，經(jīng)過本文的學(xué)習(xí)后，相信大家對(duì)MyBatis的事務(wù)管理方式這一問題有了更深刻的體會(huì)，具體使用情況還需要大家實(shí)踐驗(yàn)證。這里是創(chuàng)新互聯(lián)建站，小編將為大家推送更多相關(guān)知識(shí)點(diǎn)的文章，歡迎關(guān)注！
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