MyBatis执行流程剖析
本文详细解析了MyBatis的执行流程，包括从配置文件加载到执行SQL语句的全过程，涵盖了核心组件的功能及相互间的关系。
Mybatis源码分析
目录
1、mybatis-config.xml获取sqlSessionFactory对象
2、根据sqlSessionFactory获取SqlSession对象
一、 架构图
二、核心组件
- Configuration：用于描述 MyBatis 主配置文件信息，MyBatis 框架在启动时会加载主配置文件，将配置信息转换为 Configuration 对象。
- SqlSession：面向用户的 API，是 MyBatis 与数据库交互的接口。
- Executor：SQL 执行器，用于和数据库交互。SqlSession 可以理解为 Executor 组件的外观（外观模式），真正执行 SQL 的是 Executor 组件。
- MappedStatement：用于描述 SQL 配置信息，MyBatis 框架启动时，XML 文件或者注解配置的 SQL 信息会被转换为 MappedStatement 对象注册到 Configuration 组件中。
- StatementHandler：封装了对 JDBC 中 Statement 对象的操作，包括为 Statement 参数占位符设置值，通过 Statement 对象执行 SQL 语句。
- TypeHandler：类型处理器，用于 Java 类型与 JDBC 类型之间的转换。
- ParameterHandler：用于处理 SQL 中的参数占位符，为参数占位符设置值。
- ResultSetHandler：封装了对 ResultSet 对象的处理逻辑，将结果集转换为 Java 实体对象
三、源码分析
1、mybatis-config.xml获取sqlSessionFactory对象
代码入口：
FileReader fr=new FileReader("mybatis-config.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(fr);
SqlSession sqlSession = factory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//mapper.
userMapper.findById(3);进入到SqlSessionFactoryBuilder.build方法可以看出是通过XMLConfigBuilder 来解析xml文件，XMLConfigBuilder.parse 方法将xml的解析的信息放入Configuration对象中，parse方法调用parseConfiguration来解析 mybatis配置文件信息
public Configuration parse() {
//防止parse()方法被一个实例多次调用
if (parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
}
parsed = true;
// XPathParser.evalNode():创建表示configuration节点的XNode对象
//parseConfiguration():对XNode进行处理
parseConfiguration(parser.evalNode("/configuration"));
return configuration;
}
private void parseConfiguration(XNode root) {
try {
// 解析<properties>节点
propertiesElement(root.evalNode("properties"));
// 解析<settings>节点
Properties settings = settingsAsProperties(root.evalNode("settings"));
loadCustomVfs(settings);
// 解析<typeAliases>节点
typeAliasesElement(root.evalNode("typeAliases"));
// 解析<plugins>节点
pluginElement(root.evalNode("plugins"));
// 解析<objectFactory>节点
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
// 解析<reflectorFactory>节点
reflectorFactoryElement(root.evalNode("reflectorFactory"));
settingsElement(settings);
// 解析<environments>节点
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
// 解析<mappers>节点
mapperElement(root.evalNode("mappers"));
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}}
2、根据sqlSessionFactory获取SqlSession对象
获取sqlSessionFactory对象之后，调用openSessionFromDataSource方法返回sqlSession对象， 该方法的重要操作有两步，第一步是根据我们设置的Environment获取到对应的事物，第二步是根据事物和 executor的type来构造一个Executor
/*
*execType 执行器类型 默认传入了ExecutorType.SIMPLE;
*level 事物的隔离级别 默认传null
* autoCommit 事物是否自动提交 默认为false
**/
private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level,
boolean autoCommit) {
Transaction tx = null;
try {
//获取到配置中设置的当前环境 里面包含了环境id 数据库信息 和事物信息
//我们在构建的时候已经构建了一个environment
final Environment environment = configuration.getEnvironment();
//根据环境获取其事物级别，如果环境为空或者其事物级别为空则返回默认的ManagedTransactionFactory，
//我们使用SPring集成 所以会使用Spring的事物管理器 SpringManagedTransactionFactory
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
//根据数据源，事物隔离级别，是否自动提交生成事物管理器
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
//根据事物和执行器类别生成执行器
//由于二级缓存默认打开 所以这儿的SimpleExecutor会被包装为CacheExecutor
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();
}
}
3、获取Mapper
DefaultSqlSession#getMapper
@Override
public <T> T getMapper(Class<T> type) {
return configuration.getMapper(type, this);
}
Configuration#getMapper
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
mapperRegistry.getMapper是从MapperRegistry的knownMappers里面取的,knownMappers里面存的是接口类型(interface mapper.UserMapper)和工厂类 MapperProxyFactory
从knownMappers的Map里根据接口类型(interface mapper.UserMapper)取出对应的工厂类
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>)
knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}MapperProxyFactory#newInstance
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
//通过JDK动态代理返回代理对象MapperProxy
protected T newInstance(MapperProxy<T> mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, map
4、mybatis执行SQL语句源码分析
获取到DefaultSqlSession和Mapper，那么sql怎么执行呢，我们回到MapperProxy.invoke方法： MapperProxy#invoke():
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
//首先判断方式是不是Object类里面的方法（如：toString，hashCode），如果是Object类里面的方法就直接执行
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
}
//如果是接口默认方法
if (this.isDefaultMethod(method)) {
return this.invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable var5) {
throw ExceptionUtil.unwrapThrowable(var5);
}
//如果是接口里面的方法，会包装成MapperMethod，执行execute方法
MapperMethod mapperMethod = this.cachedMapperMethod(method);
return mapperMethod.execute(this.sqlSession, args);
}mapper.execute 方法
public Object execute(SqlSession sqlSession, Object[] args) {
Object result;
Object param;
switch(this.command.getType()) {
case INSERT:
param = this.method.convertArgsToSqlCommandParam(args);
result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));
break;
case UPDATE:
param = this.method.convertArgsToSqlCommandParam(args);
result = this.rowCountResult(sqlSession.update(this.command.getName(), param));
break;
case DELETE:
param = this.method.convertArgsToSqlCommandParam(args);
result = this.rowCountResult(sqlSession.delete(this.command.getName(), param));
break;
case SELECT:
if (this.method.returnsVoid() && this.method.hasResultHandler()) {
this.executeWithResultHandler(sqlSession, args);
result = null;
} else if (this.method.returnsMany()) {
result = this.executeForMany(sqlSession, args);
} else if (this.method.returnsMap()) {
result = this.executeForMap(sqlSession, args);
} else if (this.method.returnsCursor()) {
result = this.executeForCursor(sqlSession, args);
} else {
param = this.method.convertArgsToSqlCommandParam(args);
result = sqlSession.selectOne(this.command.getName(), param);
if (this.method.returnsOptional() && (result == null || !this.method.getReturnType().equals(result.getClass()))) {
result = Optional.ofNullable(result);
}
}
break;
case FLUSH:
result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + this.command.getName());
}
if (result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) {
throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ").");
} else {
return result;
}
}获得SQL语句的类型，比如说select，从selectOne 入口
把传进来的args参数转换成我们能用的参数
// 把传进来的args参数转换成我们能用的参数
public Object convertArgsToSqlCommandParam(Object[] args) {
return this.paramNameResolver.getNamedParams(args);
}
public Object getNamedParams(Object[] args) {
int paramCount = this.names.size();
if (args != null && paramCount != 0) {
if (!this.hasParamAnnotation && paramCount == 1) {
return args[(Integer)this.names.firstKey()];
} else {
Map<String, Object> param = new ParamMap();
int i = 0;
for(Iterator var5 = this.names.entrySet().iterator(); var5.hasNext(); ++i) {
Entry<Integer, String> entry = (Entry)var5.next();
param.put((String)entry.getValue(), args[(Integer)entry.getKey()]);
String genericParamName = "param" + String.valueOf(i + 1);
if (!this.names.containsValue(genericParamName)) {
param.put(genericParamName, args[(Integer)entry.getKey()]);
}
}
return param;
}
} else {
return null;
}
}再执行DefaultSqlSession#selectOne(statement,parameter)
public <T> T selectOne(String statement, Object parameter) {
List<T> list = this.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;
}
}
public <E> List<E> selectList(String statement, Object parameter) {
//RowBounds 实现简单逻辑分页， 对ResultSet结果集进行分页
return this.selectList(statement, parameter, RowBounds.DEFAULT);
}
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
List var5;
try {
//从configuration中获得MappedStatement对象，作为参数传给Executor.query()方法
MappedStatement ms = this.configuration.getMappedStatement(statement);
var5 = this.executor.query(ms, this.wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
} catch (Exception var9) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + var9, var9);
} finally {
ErrorContext.instance().reset();
}
return var5;
}Executor#query
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
BoundSql boundSql = ms.getBoundSql(parameter);
CacheKey key = this.createCacheKey(ms, parameter, rowBounds, boundSql);
return this.query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
....................
//从以及缓存里面获取数据，判断是否有数据，如果有数据，直接从缓存中间去获取数据
if (list != null) {
this.handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
} else {
//如果缓存中没有数据，就调用queryFromDatabase（）方法,从数据库查询
list = this.queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
}
} finally {
--this.queryStack;
}
....................
return list;
}
}
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
this.localCache.putObject(key, ExecutionPlaceholder.EXECUTION_PLACEHOLDER);
List list;
try {
list = this.doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
} finally {
this.localCache.removeObject(key);
}
//将查询的结果放入缓存
this.localCache.putObject(key, list);
if (ms.getStatementType() == StatementType.CALLABLE) {
this.localOutputParameterCache.putObject(key, parameter);
}
return list;
}最终调用SimpleExecutor的doQuery方法
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null; //原生JDBC对象
List list;
try {
Configuration configuration = ms.getConfiguration();
//创建StatementHandler 对象，由StatementHandler生成Statement
StatementHandler handler = configuration.newStatementHandler(this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
stmt = this.prepareStatement(handler, ms.getStatementLog());
list= handler.query(stmt, resultHandler);
} finally {
this.closeStatement(stmt);
}
return list;
}好了，到这里，会继续交给StatementHandler去执行
//StatementHandler有2个实现类，BaseStatementHandler和RoutingStatementHandler
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
StatementHandler statementHandler = (StatementHandler)this.interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
switch(ms.getStatementType()) {
case STATEMENT:
//管理 Statement 对象并向数据库中推送不需要预编译的SQL语句
this.delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case PREPARED:
//管理 Statement 对象并向数据中推送需要预编译的SQL语句
this.delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
case CALLABLE:
//管理 Statement 对象并调用数据库中的存储过程
this.delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
break;
default:
throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
}
}再来看看prepareStatement，如下
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Connection connection = this.getConnection(statementLog);
///////////////////////////////////////
Statement stmt = handler.prepare(connection, this.transaction.getTimeout());
handler.parameterize(stmt);
return stmt;
}
//调用的是BaseStatementHandler.prepare
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
ErrorContext.instance().sql(this.boundSql.getSql());
Statement statement = null;
try {
//////////////////////////////////////////////////////////////
statement = this.instantiateStatement(connection);
this.setStatementTimeout(statement, transactionTimeout);
this.setFetchSize(statement);
return statement;
} catch (SQLException var5) {
this.closeStatement(statement);
throw var5;
} catch (Exception var6) {
this.closeStatement(statement);
throw new ExecutorException("Error preparing statement. Cause: " + var6, var6);
}
}
protected Statement instantiateStatement(Connection connection) throws SQLException {
String sql = this.boundSql.getSql();
if (this.mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
String[] keyColumnNames = this.mappedStatement.getKeyColumns();
//最终是调用JDBC的connection.prepareStatement方法绑定执行sql并得到Statement
return keyColumnNames == null ? connection.prepareStatement(sql, 1) : connection.prepareStatement(sql, keyColumnNames);
} else {
return this.mappedStatement.getResultSetType() == ResultSetType.DEFAULT ? connection.prepareStatement(sql) : connection.prepareStatement(sql, this.mappedStatement.getResultSetType().getValue(), 1007);
}
}再回来看handler.parameterize(stmt);主要是把入参绑定到Statement里
@Override
public void parameterize(Statement statement) throws SQLException {
parameterHandler.setParameters((PreparedStatement) statement);
}在这里其实是交给ParameterHandler的唯一实现类DefaultParameterHandler来做绑定参数的工作， DefaultParameterHandler.setParameters方法如下
public void setParameters(PreparedStatement ps) {
.......................
List<ParameterMapping> parameterMappings = this.boundSql.getParameterMappings();
if (parameterMappings != null) {
//在这里，通过boundSql获取到参数集合，然后循环集合，获取到TypeHandler，在通过对应的TypeHandler绑定入参
for(int i = 0; i < parameterMappings.size(); ++i) {
ParameterMapping parameterMapping = (ParameterMapping)parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
.................
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = this.configuration.getJdbcTypeForNull();
}
try {
//参数绑定到PreparedStatement中
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException var10) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + var10, var10);
} catch (SQLException var11) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + var11, var11);
}
}
}
}
}回到SimpleExecutor.doQuery，看一下StatementHandler.query,看实现类PreparedStatementHandler.query,如下
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
ps.execute();
return resultSetHandler.handleResultSets(ps);
}这里直接就执行了!!!然后由ResultHandler.handleResultSets处理执行结果,调用的是DefaultResultSetHandler
扫一扫
191
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
