mybatis工作流程&源码详解
该篇主要讲解的是mybatis从seesion创建到执行sql语句的流程
流程主线:
1.创建SqlSessionFactoryBuilder
2.创建会话工厂SqlSessionFactory
3.创建执行实例Executor(实现类有BatchExecutor,ReuseExecutor,SimpleExecutor以及CachingExecutor)
4.创建会话SqlSession
5. 创建执行器StatementHandler(实现类有SimpleStatementHandler,CallableStatementHandler,PreparedStatementHandler以及RoutingStatementHandler)
6.执行JDBC操作
SqlSessionFactoryBuilder
public class SqlSessionFactoryBuilder {
//创建SqlSessionFactory
public SqlSessionFactory build(Reader reader) {
return build(reader, null, null);
}
//创建SqlSessionFactory
public SqlSessionFactory build(Reader reader, String environment) {
return build(reader, environment, null);
}
//创建SqlSessionFactory
public SqlSessionFactory build(Reader reader, Properties properties) {
return build(reader, null, properties);
}
//创建SqlSessionFactory
public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
try { //解析配置文件
XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
reader.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
//创建SqlSessionFactory
public SqlSessionFactory build(InputStream inputStream) {
return build(inputStream, null, null);
}
//创建SqlSessionFactory
public SqlSessionFactory build(InputStream inputStream, String environment) {
return build(inputStream, environment, null);
}
//创建SqlSessionFactory
public SqlSessionFactory build(InputStream inputStream, Properties properties) {
return build(inputStream, null, properties);
}
//创建SqlSessionFactory
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
try { //解析配置文件
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
return build(parser.parse());
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error building SqlSession.", e);
} finally {
ErrorContext.instance().reset();
try {
inputStream.close();
} catch (IOException e) {
// Intentionally ignore. Prefer previous error.
}
}
}
//创建SqlSessionFactory
public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
}
}
DefaultSqlSessionFactory
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); //创建事务
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit); //创建执行实例
final Executor executor = configuration.newExecutor(tx, execType); //创建会话session
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 SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
try {
boolean autoCommit;
try {
autoCommit = connection.getAutoCommit();
} catch (SQLException e) {
// Failover to true, as most poor drivers
// or databases won't support transactions
autoCommit = true;
}
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment); //创建事务
final Transaction tx = transactionFactory.newTransaction(connection); //创建执行实例
final Executor executor = configuration.newExecutor(tx, execType); //创建会话session
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
创建执行实例 final Executor executor = configuration.newExecutor(tx, execType);
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor; //生成不同的实现类
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
executor = new SimpleExecutor(this, transaction);
}
if (cacheEnabled) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
创建会话session new DefaultSqlSession(configuration, executor, autoCommit);
// 这里是一部分源码public class DefaultSqlSession implements SqlSession {
//持有配置对象(内部就包含了sql语句的元数据)
private Configuration configuration; //持有执行实例
private Executor executor;
private boolean autoCommit;
private boolean dirty;
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
public DefaultSqlSession(Configuration configuration, Executor executor) {
this(configuration, executor, false);
}
public <T> T selectOne(String statement) {
return this.<T>selectOne(statement, null);
}
public <T> T selectOne(String statement, Object parameter) {
// Popular vote was to return null on 0 results and throw exception on too many.
List<T> list = this.<T>selectList(statement, parameter);
if (list.size() == 1) {
return list.get(0);
} else if (list.size() > 1) {
throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
} else {
return null;
}
} //以下源码部分省略......
}
执行实例Executor持有执行器StatementHandler
以SimpleExecutor为例
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(); //根据对应场景生成不同的执行器
StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
stmt = prepareStatement(handler, ms.getStatementLog());
return handler.update(stmt);
} 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(); //根据不同的场景生成不同的执行器
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();
}
//执行JDBC
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
Connection connection = getConnection(statementLog);
stmt = handler.prepare(connection);
handler.parameterize(stmt);
return stmt;
}
}
备注:
如果自定义sql拦截器
当我们需要改变sql的时候,显然我们要在预编译SQL(prepare方法前加入修改的逻辑)。
当我们需要修改参数的时候我们可以在调用parameterize方法前修改逻辑。或者使用ParameterHandler来改造设置参数。
我们需要控制组装结果集的时候,也可以在query方法前后加入逻辑,或者使用ResultHandler来改造组装结果。
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