DefaultSqlSession第一讲query解析

上一篇文章：我们说过DefaultSqlSession，DefaultSqlSessionFactory根据执行器类型，事务级别，是否提交等信息，来构建执行器Executor，然后根据执行器和configuration构建SqlSession，默认为DefaultSqlSession，从DefaultSqlSession的类信息方法来看，DefaultSqlSession的查询则委托给executor的query，插入，更新，删除，则委托给executor的update，提交，回滚，清除缓存，刷新Statement，关闭SqlSession，都是委托给Executor的相应方法。这一节节我们来Executor
//执行器的构建
//根据数据源，事务级别，是否自动提交,创建执行器

org.apache.ibatis.executor.Executor executor = configuration.newExecutor(tx, execType, autoCommit);

//Configuration

public Executor newExecutor(Transaction transaction, ExecutorType executorType, boolean autoCommit)
    {
        executorType = executorType != null ? executorType : defaultExecutorType;
        executorType = executorType != null ? executorType : ExecutorType.SIMPLE;
        Executor executor;
        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, autoCommit);
	//将执行器插入到拦截器链中
        executor = (Executor)interceptorChain.pluginAll(executor);
        return executor;
}

从上面configuration的创建执行器方法，可以看出执行器有BatchExecutor，ReuseExecutor，SimpleExecutor
根据执行器类型，创建执行器，如果缓存启用，则包装executor为CachingExecutor；
//BatchExecutor

public class BatchExecutor extends BaseExecutor
{
    public static final int BATCH_UPDATE_RETURN_VALUE = -2147482646;
    private final List statementList = new ArrayList();
    private final List batchResultList = new ArrayList();
    private String currentSql;
    private MappedStatement currentStatement;
    public BatchExecutor(Configuration configuration, Transaction transaction)
    {
        super(configuration, transaction);
    }
}

//SimpleExecutor

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

//CachingExecutor

public class CachingExecutor
    implements Executor
{
    private Executor _flddelegate;
    private boolean autoCommit;
    private TransactionalCacheManager tcm;
    private boolean dirty;
    public CachingExecutor(Executor delegate)
    {
        this(delegate, false);
    }
    public CachingExecutor(Executor delegate, boolean autoCommit)
    {
        tcm = new TransactionalCacheManager();
        _flddelegate = delegate;
        this.autoCommit = autoCommit;
    }
    public Transaction getTransaction()
    {
        return _flddelegate.getTransaction();
    }
    //更新
    public int update(MappedStatement ms, Object parameterObject)
        throws SQLException
    {
        //刷新刷新
        flushCacheIfRequired(ms);
	//调用代理更新
        return _flddelegate.update(ms, parameterObject);
    }
    //查询
    public List 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);
    }
    //查询
    public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
        throws SQLException
    {
        Cache cache;
        cache = ms.getCache();
        if(cache == null)
            break MISSING_BLOCK_LABEL_183;
        flushCacheIfRequired(ms);
        if(!ms.isUseCache() || resultHandler != null)
            break MISSING_BLOCK_LABEL_183;
        ensureNoOutParams(ms, key, parameterObject, boundSql);
        if(dirty)
            break MISSING_BLOCK_LABEL_147;
        cache.getReadWriteLock().readLock().lock();
        List list1;
        List cachedList = (List)cache.getObject(key);
        if(cachedList == null)
            break MISSING_BLOCK_LABEL_105;
        list1 = cachedList;
        cache.getReadWriteLock().readLock().unlock();
        cache.getReadWriteLock().readLock().unlock();
        cache.getReadWriteLock().readLock().unlock();
        //调用代理查询
        List list = _flddelegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
        tcm.putObject(cache, key, list);
        return list;
        return _flddelegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

    public List flushStatements()
        throws SQLException
    {
        return _flddelegate.flushStatements();
    }

    public void commit(boolean required)
        throws SQLException
    {
        _flddelegate.commit(required);
        tcm.commit();
        dirty = false;
    }
   
    public void rollback(boolean required)
        throws SQLException
    {
        _flddelegate.rollback(required);
        dirty = false;
        if(required)
            tcm.rollback();
        break MISSING_BLOCK_LABEL_43;
        if(required)
            tcm.rollback();
        throw exception;
    }
       public void clearLocalCache()
    {
        _flddelegate.clearLocalCache();
    }
}

从上可以看出CachingExecutor是SimpleExecutor，BatchExecutor等执行器代理执行器；
事务的获取，清除缓存，更新，查询操作实际上，是调用Executor的相应方法。SimpleExecutor，
BatchExecutor为实际执行器，继承BatchExecutor；
下面根据DefaultSqlSession，来看执行器的query，update，提交，回滚，清除缓存，刷新Statement，
关闭SqlSession

public class DefaultSqlSession
    implements SqlSession
{
    private Configuration configuration;
    private Executor executor;
    private boolean dirty;
    public DefaultSqlSession(Configuration configuration, Executor executor)
    {
        this.configuration = configuration;
        this.executor = executor;
        dirty = false;
    }
    //查询
    public Object selectOne(String statement)
    {
        return selectOne(statement, null);
    }
    public Object selectOne(String statement, Object parameter)
    {
        List list = selectList(statement, parameter);
        if(list.size() == 1)
            return list.get(0);
        if(list.size() > 1)
            throw new TooManyResultsException((new StringBuilder()).append("Expected one result (or null) to be returned by selectOne(), but found: ").append(list.size()).toString());
        else
            return null;
    }
    public List selectList(String statement)
    {
        return selectList(statement, null);
    }

    public List selectList(String statement, Object parameter)
    {
        return selectList(statement, parameter, RowBounds.DEFAULT);
    }
    public List selectList(String statement, Object parameter, RowBounds rowBounds)
    {
        List list;
        try
        {
            org.apache.ibatis.mapping.MappedStatement ms = configuration.getMappedStatement(statement);
	    //调用executor的查询方法
            List result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
            list = result;
        }
    }
    //插入
     public int insert(String statement)
    {
        return insert(statement, null);
    }

    public int insert(String statement, Object parameter)
    {
       //委托给update方法
        return update(statement, parameter);
    }

    public int update(String statement)
    {
        return update(statement, null);
    }

    public int update(String statement, Object parameter)
    {
        int i;
        try
        {
            dirty = true;
            org.apache.ibatis.mapping.MappedStatement ms = configuration.getMappedStatement(statement);
            //委托给executor的update
	    i = executor.update(ms, wrapCollection(parameter));
        }
    }
    //删除
     public int delete(String statement)
    { 
        //委托给update
        return update(statement, null);
    }

    public int delete(String statement, Object parameter)
    {
        return update(statement, parameter);
    }
    //提交
     public void commit()
    {
        commit(false);
    }

    public void commit(boolean force)
    {
        try
        {
	    //委托executor的commit
            executor.commit(isCommitOrRollbackRequired(force));
            dirty = false;
        }
    }
    //回滚
     public void rollback()
    {
        rollback(false);
    }

    public void rollback(boolean force)
    {
        try
        {
	    //委托executor的rollback
            executor.rollback(isCommitOrRollbackRequired(force));
            dirty = false;
        }
    }
    //清除缓存
    public void clearCache()
    {
	////委托executor的clearLocalCache
        executor.clearLocalCache();
    }
    //刷新Statements
    public List flushStatements()
    {
        List list;
        try
        {
	    //委托executor的flushStatements
            list = executor.flushStatements();
        }
    }
    //关闭SqlSession
    public void close()
    {
        //委托executor的close
        executor.close(isCommitOrRollbackRequired(false));
        dirty = false;
    }
}

先来看SqlSession

public List selectList(String statement, Object parameter, RowBounds rowBounds)
    {
        List list;
        try
        {
            org.apache.ibatis.mapping.MappedStatement ms = configuration.getMappedStatement(statement);
	    //调用executor的查询方法
            List result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
            list = result;
        }
    }

代理执行器调用实际执行器BatchExecutor，ReuseExecutor，SimpleExecutor的query的方法
//CachingExecutor
//查询
   

public List 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);
    }
    //查询
    public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
        throws SQLException
    {
        List list = _flddelegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
        tcm.putObject(cache, key, list);
        return list;
        return _flddelegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
    }

查看BatchExecutor，ReuseExecutor，SimpleExecutor的query的方法，实际上是在BaseExecutor
//BaseExecutor

public List query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler)
        throws SQLException
    {
        BoundSql boundSql = ms.getBoundSql(parameter);
        CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
	//委托给query(ms, parameter, rowBounds, resultHandler, key, boundSql);
        return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
    }

    public List 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 list;
        queryStack++;
        list = resultHandler != null ? null : (List)localCache.getObject(key);
        if(list != null)
	    //从本地获取查询结果
            handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
        else
	    //从数据库查询结果
            list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
        return list;
    }
    //从数据库查询结果
     private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql)
        throws SQLException
    {
        localCache.putObject(key, ExecutionPlaceholder.EXECUTION_PLACEHOLDER);
	//委托给doQuery
        List list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
        localCache.removeObject(key);
        break MISSING_BLOCK_LABEL_53;
        Exception exception;
        exception;
        localCache.removeObject(key);
        throw exception;
        localCache.putObject(key, list);
        if(ms.getStatementType() == StatementType.CALLABLE)
            localOutputParameterCache.putObject(key, parameter);
        return list;
    }
    //doQuery为抽象方法，待子类扩展
     protected abstract List doQuery(MappedStatement mappedstatement, Object obj, RowBounds rowbounds, ResultHandler resulthandler, BoundSql boundsql)
        throws SQLException;

这里我们来看一下SimpleExecutor
//SimpleExecutor

public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
        throws SQLException
    {
        Statement stmt = null;
        List list;
        Configuration configuration = ms.getConfiguration();
	//构造StatementHandler
        StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, rowBounds, resultHandler, boundSql);
        //获取Statement
	stmt = prepareStatement(handler, ms.getStatementLog());
	//执行查询
        list = handler.query(stmt, resultHandler);
	//关闭statement
        closeStatement(stmt);
        return list;
        Exception exception;
        exception;
        closeStatement(stmt);
        throw exception;
    }

//构造StatementHandler

StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, rowBounds, resultHandler, boundSql);

//configuration

public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
    {
        //创建RoutingStatementHandler
        StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
        //拦截器处理statementHandler，
	statementHandler = (StatementHandler)interceptorChain.pluginAll(statementHandler);
        return statementHandler;
    }

//RoutingStatementHandler

public class RoutingStatementHandler
    implements StatementHandler
{
    private final StatementHandler _flddelegate;
    public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
    {
        static class _cls1
        {

            static final int $SwitchMap$org$apache$ibatis$mapping$StatementType[];

            static 
            {
                $SwitchMap$org$apache$ibatis$mapping$StatementType = new int[StatementType.values().length];
                try
                {
                    $SwitchMap$org$apache$ibatis$mapping$StatementType[StatementType.STATEMENT.ordinal()] = 1;
                }
                catch(NoSuchFieldError ex) { }
                try
                {
                    $SwitchMap$org$apache$ibatis$mapping$StatementType[StatementType.PREPARED.ordinal()] = 2;
                }
                catch(NoSuchFieldError ex) { }
                try
                {
                    $SwitchMap$org$apache$ibatis$mapping$StatementType[StatementType.CALLABLE.ordinal()] = 3;
                }
                catch(NoSuchFieldError ex) { }
            }
        }
       //根据StatementType，创建对应的StatementHandler
        switch(_cls1..SwitchMap.org.apache.ibatis.mapping.StatementType[ms.getStatementType().ordinal()])
        {
        case 1: // '\001'
            _flddelegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
            break;

        case 2: // '\002'
            _flddelegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
            break;

        case 3: // '\003'
            _flddelegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
            break;

        default:
            throw new ExecutorException((new StringBuilder()).append("Unknown statement type: ").append(ms.getStatementType()).toString());
        }
    }

    public Statement prepare(Connection connection)
        throws SQLException
    {
        return _flddelegate.prepare(connection);
    }

    public void parameterize(Statement statement)
        throws SQLException
    {
        _flddelegate.parameterize(statement);
    }

    public void batch(Statement statement)
        throws SQLException
    {
        _flddelegate.batch(statement);
    }

    public int update(Statement statement)
        throws SQLException
    {
        return _flddelegate.update(statement);
    }

    public List query(Statement statement, ResultHandler resultHandler)
        throws SQLException
    {
        return _flddelegate.query(statement, resultHandler);
    }

    public BoundSql getBoundSql()
    {
        return _flddelegate.getBoundSql();
    }

    public ParameterHandler getParameterHandler()
    {
        return _flddelegate.getParameterHandler();
    }
}

从RoutingStatementHandler可以看出，更新，查询，预编译都是通过代理StatementHandler，具体根据StatementType创建对应的StatementHandler，SimpleStatementHandler，PreparedStatementHandler，CallableStatementHandler
//获取Statement

stmt = prepareStatement(handler, ms.getStatementLog());
 private Statement prepareStatement(StatementHandler handler, Log statementLog)
        throws SQLException
    {
        //获取连接，这里实际上调用的为BaseExector的getConnection，从执行器的事务管理器获取连接
        java.sql.Connection connection = getConnection(statementLog);
	//预编译
        Statement stmt = handler.prepare(connection);
	//参数设置
        handler.parameterize(stmt);
        return stmt;
    }

//预编译

Statement stmt = handler.prepare(connection);

实际为RoutingStatementHandler，通过本地代理，预编译Statement，

public abstract class BaseStatementHandler
    implements StatementHandler
{
   //获取PrepareStatement
public Statement prepare(Connection connection)
        throws SQLException
    {
        protected final Configuration configuration;
        protected final ObjectFactory objectFactory;
        protected final TypeHandlerRegistry typeHandlerRegistry;
        protected final ResultSetHandler resultSetHandler;
        protected final ParameterHandler parameterHandler;
        protected final Executor executor;
        protected final MappedStatement mappedStatement;
        protected final RowBounds rowBounds;
        protected BoundSql boundSql;
        Statement statement;
        ErrorContext.instance().sql(boundSql.getSql());
        statement = null;
	//实例化Statement
        statement = instantiateStatement(connection);
        setStatementTimeout(statement);
        setFetchSize(statement);
        return statement;
    }
    //带子类扩展
     protected abstract Statement instantiateStatement(Connection connection)
        throws SQLException;
    
    //设置statement的超时时间
     protected void setStatementTimeout(Statement stmt)
        throws SQLException
    {
        Integer timeout = mappedStatement.getTimeout();
        Integer defaultTimeout = configuration.getDefaultStatementTimeout();
        if(timeout != null)
            stmt.setQueryTimeout(timeout.intValue());
        else
        if(defaultTimeout != null)
            stmt.setQueryTimeout(defaultTimeout.intValue());
    }
   //设置statement的FetchSize
    protected void setFetchSize(Statement stmt)
        throws SQLException
    {
        Integer fetchSize = mappedStatement.getFetchSize();
        if(fetchSize != null)
            stmt.setFetchSize(fetchSize.intValue());
    }
}

我们来看statement实例化：
//PreparedStatementHandler,这里我们来看PreparedStatementHandler的实例化

public class PreparedStatementHandler extends BaseStatementHandler
{

    public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
    {
        super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
    }
    //实例化Statement
    protected Statement instantiateStatement(Connection connection)
        throws SQLException
    {
        //获取sql
        String sql = boundSql.getSql();
        if(mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator)
        {
            String keyColumnNames[] = mappedStatement.getKeyColumns();
            if(keyColumnNames == null)
                return connection.prepareStatement(sql, 1);
            else
	       //从connection返回PreparedStatement
                return connection.prepareStatement(sql, keyColumnNames);
        }
        if(mappedStatement.getResultSetType() != null)
            return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), 1007);
        else
            return connection.prepareStatement(sql);
    }
}

我们再看一下
//CallableStatementHandler

public class CallableStatementHandler extends BaseStatementHandler
{
protected Statement instantiateStatement(Connection connection)
        throws SQLException
    {
        String sql = boundSql.getSql();
        if(mappedStatement.getResultSetType() != null)
            return connection.prepareCall(sql, mappedStatement.getResultSetType().getValue(), 1007);
        else
	   //从connection返回CallableStatement
            return connection.prepareCall(sql);
    }
}

从上面可以看出构造StatementHandler，实际上为RoutingStatementHandler，
RoutingStatementHandler更新，查询，预编译都是通过代理StatementHandler，具体根据StatementType创建对应的StatementHandler，SimpleStatementHandler，
PreparedStatementHandler，CallableStatementHandler，
由具体的StatementHandler,创建Statement
//参数设置

handler.parameterize(stmt);

//PreparedStatementHandler

public void parameterize(Statement statement)
        throws SQLException
    {
        parameterHandler.setParameters((PreparedStatement)statement);
    }

parameterHandler在BaseStatementHandler中

public abstract class BaseStatementHandler
    implements StatementHandler
{
    protected final Configuration configuration;
    protected final ObjectFactory objectFactory;
    protected final TypeHandlerRegistry typeHandlerRegistry;
    protected final ResultSetHandler resultSetHandler;
    protected final ParameterHandler parameterHandler;
    protected final Executor executor;
    protected final MappedStatement mappedStatement;
    protected final RowBounds rowBounds;
    protected BoundSql boundSql;
    protected BaseStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
    {
        configuration = mappedStatement.getConfiguration();
        this.executor = executor;
        this.mappedStatement = mappedStatement;
        this.rowBounds = rowBounds;
        typeHandlerRegistry = configuration.getTypeHandlerRegistry();
        objectFactory = configuration.getObjectFactory();
        if(boundSql == null)
        {
            generateKeys(parameterObject);
            boundSql = mappedStatement.getBoundSql(parameterObject);
        }
        this.boundSql = boundSql;
	//configuration创建ParameterHandler
        parameterHandler = configuration.newParameterHandler(mappedStatement, parameterObject, boundSql);
        resultSetHandler = configuration.newResultSetHandler(executor, mappedStatement, rowBounds, parameterHandler, resultHandler, boundSql);
    }
}

来看一下
//configuration创建ParameterHandler

public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql)
    {
        //从mappedStatement获取LanguageDriver，创建ParameterHandler
        ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
        //拦截器链处理ParameterHandler
	parameterHandler = (ParameterHandler)interceptorChain.pluginAll(parameterHandler);
        return parameterHandler;
    }

//XMLLanguageDriver

public class XMLLanguageDriver
    implements LanguageDriver
{
    public ParameterHandler createParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql)
    {
        return new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);
    }

//DefaultParameterHandler

public class DefaultParameterHandler
    implements ParameterHandler
{
    private final TypeHandlerRegistry typeHandlerRegistry;
    private final MappedStatement mappedStatement;
    private final Object parameterObject;
    private BoundSql boundSql;
    private Configuration configuration;
    public DefaultParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql)
    {
        this.mappedStatement = mappedStatement;
        configuration = mappedStatement.getConfiguration();
        typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();
        this.parameterObject = parameterObject;
        this.boundSql = boundSql;
    }
    //设置PreparedStatement的参数
    public void setParameters(PreparedStatement ps)
        throws SQLException
    {
        ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
        //从boundSql获取参数映射
	List parameterMappings = boundSql.getParameterMappings();
        if(parameterMappings != null)
        {
            MetaObject metaObject = parameterObject != null ? configuration.newMetaObject(parameterObject) : null;
            for(int i = 0; i < parameterMappings.size(); i++)
            {
	        //获取parameterMapping
                ParameterMapping parameterMapping = (ParameterMapping)parameterMappings.get(i);
                if(parameterMapping.getMode() == ParameterMode.OUT)
                    continue;
                String propertyName = parameterMapping.getProperty();
                Object value;
                if(boundSql.hasAdditionalParameter(propertyName))
                    value = boundSql.getAdditionalParameter(propertyName);
                else
                if(parameterObject == null)
                    value = null;
                else
                if(typeHandlerRegistry.hasTypeHandler(parameterObject.getClass()))
                    value = parameterObject;
                else
                    value = metaObject != null ? metaObject.getValue(propertyName) : null;
		//获取具体的TypeHandler
                TypeHandler typeHandler = parameterMapping.getTypeHandler();
                if(typeHandler == null)
                    throw new ExecutorException((new StringBuilder()).append("There was no TypeHandler found for parameter ").append(propertyName).append(" of statement ").append(mappedStatement.getId()).toString());
                JdbcType jdbcType = parameterMapping.getJdbcType();
                if(value == null && jdbcType == null)
                    jdbcType = configuration.getJdbcTypeForNull();
		//typeHandler设置PreparedStatement参数
                typeHandler.setParameter(ps, i + 1, value, jdbcType);
            }

        }
    }
}

//BaseTypeHandler

public abstract class BaseTypeHandler extends TypeReference
    implements TypeHandler
{
public void setParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType)
        throws SQLException
    {
        if(parameter == null)
        {
            if(jdbcType == null)
                throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
            try
            {
                ps.setNull(i, jdbcType.TYPE_CODE);
            }
        } else
        {
	    //设置参数
            setNonNullParameter(ps, i, parameter, jdbcType);
        }
    }
    //待父类扩展
    public abstract void setNonNullParameter(PreparedStatement preparedstatement, int i, Object obj, JdbcType jdbctype)
        throws SQLException;
}

BaseTypeHandler的子类有Integer，Float，Double，Boolean，Day，TimeStamp，Clob，StringTypeHandler
这里我们来看StringTypeHandler

public class StringTypeHandler extends BaseTypeHandler
{
public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType)
        throws SQLException
    {
        ps.setString(i, parameter);
    }
}

从上面可以看出，参数初始化实际上，是通过ParameterHandler来处理，ParameterHandler默认为DefaultParameterHandler，
DefaultParameterHandler初始化参数实际上，
是从boundSql获取statement参数映射parameterMappings，遍历parameterMappings
根据具体的parameterMapping，从parameterMapping获取TypeHandler
（Integer，Float，Double，Boolean，Day，TimeStamp，Clob，StringTypeHandler）
;最后由TypeHandler，去设置statement参数
//执行查询
l

ist = handler.query(stmt, resultHandler);

//PreparedStatementHandler

public List query(Statement statement, ResultHandler resultHandler)
        throws SQLException
    {
        PreparedStatement ps = (PreparedStatement)statement;
        ps.execute();
        return resultSetHandler.handleResultSets(ps);
    }

//CallableStatementHandler
 

public List query(Statement statement, ResultHandler resultHandler)
        throws SQLException
    {
        CallableStatement cs = (CallableStatement)statement;
        cs.execute();
        List resultList = resultSetHandler.handleResultSets(cs);
        resultSetHandler.handleOutputParameters(cs);
        return resultList;
    }

//关闭statement

closeStatement(stmt);

//BaseStatementHandler

protected void closeStatement(Statement statement)
    {
        if(statement != null)
            try
            {
                statement.close();
            }
            catch(SQLException e) { }
}

总结：
Sqlsession查询，通过CachingExecutor代理，CachingExecutor是SimpleExecutor，BatchExecutor等执行器代理执行器；
事务的获取，清除缓存，更新，查询操作实际上，是调用Executor的相应方法。SimpleExecutor，BatchExecutor为实际执行器，继承BatchExecutor。SimpleExecutor查询，如果有缓存，则利用缓存，没有则用从数据库中查询，查询过程，构造StatementHandler，获取Statement，执行查询，关闭statement。