Mybatis的Environment解析详解

SqlSessionFactory初始化：[url]http://donald-draper.iteye.com/blog/2331917[/url]
Mybatis加载解析Mapper（xml）文件第一讲:[url]http://donald-draper.iteye.com/blog/2333125[/url]
Mybatis加载解析Mapper（xml）文件第二讲：[url]http://donald-draper.iteye.com/blog/2333191[/url]
Mybatis 解析Mapper（class）：[url]http://donald-draper.iteye.com/blog/2333293[/url]
//全局文件的解析的方法在XMLConfigBuilder中，今天来具体看一下如何解析environments
//XMLConfigBuilder

private void parseConfiguration(XNode root)
    {
        try
        {
            propertiesElement(root.evalNode("properties"));
            typeAliasesElement(root.evalNode("typeAliases"));
            pluginElement(root.evalNode("plugins"));
            objectFactoryElement(root.evalNode("objectFactory"));
            objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
            settingsElement(root.evalNode("settings"));
	    //解析environments
            environmentsElement(root.evalNode("environments"));
            databaseIdProviderElement(root.evalNode("databaseIdProvider"));
            typeHandlerElement(root.evalNode("typeHandlers"));
            mapperElement(root.evalNode("mappers"));
        }
        catch(Exception e)
        {
            throw new BuilderException((new StringBuilder()).append("Error parsing SQL Mapper Configuration. Cause: ").append(e).toString(), e);
        }
    }
//解析environments
private void environmentsElement(XNode context)
        throws Exception
    {
        if(context != null)
        {
            if(C == null)
                environment = context.getStringAttribute("default");
            Iterator i$ = context.getChildren().iterator();
	    //遍历environments的child节点environment，并解析
            do
            {
                if(!i$.hasNext())
                    break;
                XNode child = (XNode)i$.next();
                String id = child.getStringAttribute("id");
		//如果environment的id属性，与environments的default相同时，才解析
                if(isSpecifiedEnvironment(id))
                {
		    //解析transactionManager
                    TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
                    //解析dataSource
		    DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
                    javax.sql.DataSource dataSource = dsFactory.getDataSource();
                    org.apache.ibatis.mapping.Environment.Builder environmentBuilder = (new org.apache.ibatis.mapping.Environment.Builder(id)).transactionFactory(txFactory).dataSource(dataSource);
                    configuration.setEnvironment(environmentBuilder.build());
                }
            } while(true);
        }
    }

//解析transactionManager
先看configuration的构造，启动有JDBC，POOLED类型的映射关系，这个在解析environment节点时，需要用到

typeAliasRegistry.registerAlias("JDBC", org/apache/ibatis/transaction/jdbc/JdbcTransactionFactory);
typeAliasRegistry.registerAlias("POOLED", org/apache/ibatis/datasource/pooled/PooledDataSourceFactory);

public Configuration()
    {
        safeRowBoundsEnabled = false;
        safeResultHandlerEnabled = true;
        mapUnderscoreToCamelCase = false;
        aggressiveLazyLoading = true;
        multipleResultSetsEnabled = true;
        useGeneratedKeys = false;//允许JDBC支持生成的键
        useColumnLabel = true;
        cacheEnabled = true;//全局的映射器启用或禁用缓存
        callSettersOnNulls = false;
        localCacheScope = LocalCacheScope.SESSION;//本地一级缓存作用域
        jdbcTypeForNull = JdbcType.OTHER;
        lazyLoadTriggerMethods = new HashSet(Arrays.asList(new String[] {
            "equals", "clone", "hashCode", "toString"
        }));
        defaultExecutorType = ExecutorType.SIMPLE;
        autoMappingBehavior = AutoMappingBehavior.PARTIAL;
        variables = new Properties();
        objectFactory = new DefaultObjectFactory();//默认ObjectFactory
        objectWrapperFactory = new DefaultObjectWrapperFactory();//默认DefaultObjectWrapperFactory
        mapperRegistry = new MapperRegistry(this);
        lazyLoadingEnabled = false;
        interceptorChain = new InterceptorChain();//插件链
        typeHandlerRegistry = new TypeHandlerRegistry();//类型处理注册器
        typeAliasRegistry = new TypeAliasRegistry();//类型别名注册器
        languageRegistry = new LanguageDriverRegistry();
	//mappedStatements Map
        mappedStatements = new StrictMap("Mapped Statements collection");
	//mappedStatements，method，二级缓存
        caches = new StrictMap("Caches collection");
	//MapperInterface 方法返回结果类型Map
        resultMaps = new StrictMap("Result Maps collection");
        //MapperInterface 方法参数类型Map
        parameterMaps = new StrictMap("Parameter Maps collection");
	//主键生成器Map
        keyGenerators = new StrictMap("Key Generators collection");
        loadedResources = new HashSet();
	//Mapper.xml 中statement片段
        sqlFragments = new StrictMap("XML fragments parsed from previous mappers");
	//未解析处理的statements
        incompleteStatements = new LinkedList();
	//未解析处理的CacheRefs
        incompleteCacheRefs = new LinkedList();
	//未解析处理的ResultMaps
        incompleteResultMaps = new LinkedList();
	//未解析处理的Methods
        incompleteMethods = new LinkedList();
        cacheRefMap = new HashMap();
        typeAliasRegistry.registerAlias("JDBC", org/apache/ibatis/transaction/jdbc/JdbcTransactionFactory);
        typeAliasRegistry.registerAlias("MANAGED", org/apache/ibatis/transaction/managed/ManagedTransactionFactory);
        typeAliasRegistry.registerAlias("JNDI", org/apache/ibatis/datasource/jndi/JndiDataSourceFactory);
        typeAliasRegistry.registerAlias("POOLED", org/apache/ibatis/datasource/pooled/PooledDataSourceFactory);
        typeAliasRegistry.registerAlias("UNPOOLED", org/apache/ibatis/datasource/unpooled/UnpooledDataSourceFactory);
        typeAliasRegistry.registerAlias("PERPETUAL", org/apache/ibatis/cache/impl/PerpetualCache);
        typeAliasRegistry.registerAlias("FIFO", org/apache/ibatis/cache/decorators/FifoCache);
        typeAliasRegistry.registerAlias("LRU", org/apache/ibatis/cache/decorators/LruCache);
        typeAliasRegistry.registerAlias("SOFT", org/apache/ibatis/cache/decorators/SoftCache);
        typeAliasRegistry.registerAlias("WEAK", org/apache/ibatis/cache/decorators/WeakCache);
        typeAliasRegistry.registerAlias("VENDOR", org/apache/ibatis/mapping/VendorDatabaseIdProvider);
        typeAliasRegistry.registerAlias("XML", org/apache/ibatis/scripting/xmltags/XMLLanguageDriver);
        typeAliasRegistry.registerAlias("RAW", org/apache/ibatis/scripting/defaults/RawLanguageDriver);
        typeAliasRegistry.registerAlias("SLF4J", org/apache/ibatis/logging/slf4j/Slf4jImpl);
        typeAliasRegistry.registerAlias("COMMONS_LOGGING", org/apache/ibatis/logging/commons/JakartaCommonsLoggingImpl);
        typeAliasRegistry.registerAlias("LOG4J", org/apache/ibatis/logging/log4j/Log4jImpl);
        typeAliasRegistry.registerAlias("JDK_LOGGING", org/apache/ibatis/logging/jdk14/Jdk14LoggingImpl);
        typeAliasRegistry.registerAlias("STDOUT_LOGGING", org/apache/ibatis/logging/stdout/StdOutImpl);
        typeAliasRegistry.registerAlias("NO_LOGGING", org/apache/ibatis/logging/nologging/NoLoggingImpl);
        typeAliasRegistry.registerAlias("CGLIB", org/apache/ibatis/executor/loader/CglibProxyFactory);
        typeAliasRegistry.registerAlias("JAVASSIST", org/apache/ibatis/executor/loader/JavassistProxyFactory);
        languageRegistry.setDefaultDriverClass(org/apache/ibatis/scripting/xmltags/XMLLanguageDriver);
        languageRegistry.register(org/apache/ibatis/scripting/defaults/RawLanguageDriver);
    }

从上可以看出JDBC，POOLED类型别名的映射关系如下：
JDBC，JdbcTransactionFactory
POOLED，PooledDataSourceFactory

<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="${driver}" />
				<property name="url" value="${url}" />
				<property name="username" value="${username}" />
				<property name="password" value="${password}" />
			</dataSource>
		</environment>
</environments>

private TransactionFactory transactionManagerElement(XNode context)
        throws Exception
    {
        if(context != null)
        {
            String type = context.getStringAttribute("type");
            Properties props = context.getChildrenAsProperties();
	    //从类型解决器中，获取type对应的类型的实例，从上面的配置来看
	    //实际为JdbcTransactionFactory
            TransactionFactory factory = (TransactionFactory)resolveClass(type).newInstance();
	    //设置JdbcTransactionFactory属性
            factory.setProperties(props);
            return factory;
        } else
        {
            throw new BuilderException("Environment declaration requires a TransactionFactory.");
        }
    }

//JdbcTransactionFactory

public class JdbcTransactionFactory
    implements TransactionFactory
{
    public void setProperties(Properties properties)
    {
    }
   //根据数据连接新建事务
    public Transaction newTransaction(Connection conn)
    {
        return new JdbcTransaction(conn);
    }
    //根据数据源和事务级别和是否自动提交，新建事务
    public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit)
    {
        return new JdbcTransaction(ds, level, autoCommit);
    }
}

//TransactionFactory

public interface TransactionFactory
{
    public abstract void setProperties(Properties properties);
    public abstract Transaction newTransaction(Connection connection);
    public abstract Transaction newTransaction(DataSource datasource, TransactionIsolationLevel transactionisolationlevel, boolean flag);
}

现在来看一下jdbc事务

public class JdbcTransaction
    implements Transaction
{
    private static final Log log = LogFactory.getLog(org/apache/ibatis/transaction/jdbc/JdbcTransaction);
    protected Connection connection;//数据库连接
    protected DataSource dataSource;//数据源
    protected TransactionIsolationLevel level;//事务级别
    protected boolean autoCommmit;//自动提交属性

    public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit)
    {
        dataSource = ds;
        level = desiredLevel;
        autoCommmit = desiredAutoCommit;
    }

    public JdbcTransaction(Connection connection)
    {
        this.connection = connection;
    }

    public Connection getConnection()
        throws SQLException
    {
        if(connection == null)
            openConnection();
        return connection;
    }

    public void commit()
        throws SQLException
    {
        if(connection != null && !connection.getAutoCommit())
        {
            if(log.isDebugEnabled())
                log.debug((new StringBuilder()).append("Committing JDBC Connection [").append(connection).append("]").toString());
            connection.commit();
        }
    }

    public void rollback()
        throws SQLException
    {
        if(connection != null && !connection.getAutoCommit())
        {
            if(log.isDebugEnabled())
                log.debug((new StringBuilder()).append("Rolling back JDBC Connection [").append(connection).append("]").toString());
            connection.rollback();
        }
    }

    public void close()
        throws SQLException
    {
        if(connection != null)
        {
            resetAutoCommit();
            if(log.isDebugEnabled())
                log.debug((new StringBuilder()).append("Closing JDBC Connection [").append(connection).append("]").toString());
            connection.close();
        }
    }

    protected void setDesiredAutoCommit(boolean desiredAutoCommit)
    {
        try
        {
            if(connection.getAutoCommit() != desiredAutoCommit)
            {
                if(log.isDebugEnabled())
                    log.debug((new StringBuilder()).append("Setting autocommit to ").append(desiredAutoCommit).append(" on JDBC Connection [").append(connection).append("]").toString());
                connection.setAutoCommit(desiredAutoCommit);
            }
        }
        catch(SQLException e)
        {
            throw new TransactionException((new StringBuilder()).append("Error configuring AutoCommit.  Your driver may not support getAutoCommit() or setAutoCommit(). Requested setting: ").append(desiredAutoCommit).append(".  Cause: ").append(e).toString(), e);
        }
    }

    protected void resetAutoCommit()
    {
        try
        {
            if(!connection.getAutoCommit())
            {
                if(log.isDebugEnabled())
                    log.debug((new StringBuilder()).append("Resetting autocommit to true on JDBC Connection [").append(connection).append("]").toString());
                connection.setAutoCommit(true);
            }
        }
        catch(SQLException e)
        {
            log.debug((new StringBuilder()).append("Error resetting autocommit to true before closing the connection.  Cause: ").append(e).toString());
        }
    }
    //获取connection
    protected void openConnection()
        throws SQLException
    {
        if(log.isDebugEnabled())
            log.debug("Openning JDBC Connection");
        connection = dataSource.getConnection();
        if(level != null)
            connection.setTransactionIsolation(level.getLevel());
        setDesiredAutoCommit(autoCommmit);
    }
}

//Transaction

public interface Transaction
{

    public abstract Connection getConnection()
        throws SQLException;

    public abstract void commit()
        throws SQLException;

    public abstract void rollback()
        throws SQLException;

    public abstract void close()
        throws SQLException;
}

从上面可以看出jdbc对应的事务工厂为JdbcTransactionFactory，由JdbcTransactionFactory，根据数据源，事务级别以及自动提交属性来，创建JdbcTransaction，而JdbcTransaction的事务管理，是通过数据连接connection，而connection是从datasource获取，JdbcTransaction的事务管理，就是依靠相应的数据库driver，来管理，实际依赖于数据库。

//解析dataSource

private DataSourceFactory dataSourceElement(XNode context)
        throws Exception
    {
        if(context != null)
        {
	    //获取数据源的类型，和属性
            String type = context.getStringAttribute("type");
            Properties props = context.getChildrenAsProperties();
	    //根据type从configuration的类型处理器，获取具体的DataSourceFactory
	    //从上文，我们看一看到type为POOLED，对应的是PooledDataSourceFactory
            DataSourceFactory factory = (DataSourceFactory)resolveClass(type).newInstance();
            factory.setProperties(props);
            return factory;
        } else
        {
            throw new BuilderException("Environment declaration requires a DataSourceFactory.");
        }
    }

// PooledDataSourceFactory

public class PooledDataSourceFactory extends UnpooledDataSourceFactory
{

    public PooledDataSourceFactory()
    {
        dataSource = new PooledDataSource();
    }
}

//UnpooledDataSourceFactory

public class UnpooledDataSourceFactory
    implements DataSourceFactory
{
    private static final String DRIVER_PROPERTY_PREFIX = "driver.";
    private static final int DRIVER_PROPERTY_PREFIX_LENGTH = "driver.".length();
    protected DataSource dataSource;

    public UnpooledDataSourceFactory()
    {
        dataSource = new UnpooledDataSource();
    }

    public void setProperties(Properties properties)
    {
        Properties driverProperties = new Properties();
	//获取dataSource的对象描述
        MetaObject metaDataSource = SystemMetaObject.forObject(dataSource);
	//获取dataSource的所有属性，并设置
        for(Iterator i$ = properties.keySet().iterator(); i$.hasNext();)
        {
            Object key = i$.next();
            String propertyName = (String)key;
            if(propertyName.startsWith("driver."))
            {
                String value = properties.getProperty(propertyName);
                driverProperties.setProperty(propertyName.substring(DRIVER_PROPERTY_PREFIX_LENGTH), value);
            } else
            if(metaDataSource.hasSetter(propertyName))
            {
                String value = (String)properties.get(propertyName);
                Object convertedValue = convertValue(metaDataSource, propertyName, value);
                metaDataSource.setValue(propertyName, convertedValue);
            } else
            {
                throw new DataSourceException((new StringBuilder()).append("Unknown DataSource property: ").append(propertyName).toString());
            }
        }
        //设置metaDataSource的driverProperties属性
        if(driverProperties.size() > 0)
            metaDataSource.setValue("driverProperties", driverProperties);
    }

    public DataSource getDataSource()
    {
        return dataSource;
    }
    //将value转化为metaDataSource的对应setValue的参数类型
    private Object convertValue(MetaObject metaDataSource, String propertyName, String value)
    {
        Object convertedValue = value;
        Class targetType = metaDataSource.getSetterType(propertyName);
        if(targetType == java/lang/Integer || targetType == Integer.TYPE)
            convertedValue = Integer.valueOf(value);
        else
        if(targetType == java/lang/Long || targetType == Long.TYPE)
            convertedValue = Long.valueOf(value);
        else
        if(targetType == java/lang/Boolean || targetType == Boolean.TYPE)
            convertedValue = Boolean.valueOf(value);
        return convertedValue;
    }

}

//PooledDataSource

public class PooledDataSource
    implements DataSource
{
    private final PoolState state;
    private final UnpooledDataSource dataSource;
    protected int poolMaximumActiveConnections;
    protected int poolMaximumIdleConnections;
    protected int poolMaximumCheckoutTime;
    protected int poolTimeToWait;
    protected String poolPingQuery;
    protected boolean poolPingEnabled;
    protected int poolPingConnectionsNotUsedFor;
    private int expectedConnectionTypeCode;

}

从上面可以看出解析datasource节点，就是解析器属性，并初始化datasource，
PooledDataSourceFactory继承UnpooledDataSourceFactory，改变的只是数据源类型，
PooledDataSourceFactory对应的数据源为PooledDataSource，而UnpooledDataSourceFactory对应的为，UnpooledDataSource；
我们再来看解析environment节点是，environment的构造

 org.apache.ibatis.mapping.Environment.Builder environmentBuilder = 
 (new org.apache.ibatis.mapping.Environment.Builder(id)).transactionFactory(txFactory).dataSource(dataSource);

//Environment

public final class Environment
{
    private final String id;
    private final TransactionFactory transactionFactory;
    private final DataSource dataSource;

    public static class Builder
    {
        public Environment build()
        {
            return new Environment(id, transactionFactory, dataSource);
        }

        private String id;
        private TransactionFactory transactionFactory;
        private DataSource dataSource;
        public Builder(String id)
        {
            this.id = id;
        }
    }
}

再来看，Configuration设置environment

public void setEnvironment(Environment environment)
    {
        this.environment = environment;
    }

总结：
[color=blue]事务类型为jdbc对应的事务工厂为JdbcTransactionFactory，由JdbcTransactionFactory，根据数据源，事务级别以及自动提交属性来，创建JdbcTransaction，而JdbcTransaction的事务管理，是通过数据连接connection，而connection是从datasource获取，JdbcTransaction的事务管理，就是依靠相应的数据库driver，来管理，实际依赖于数据库；解析datasource节点，就是解析器属性，并初始化datasource，PooledDataSourceFactory继承UnpooledDataSourceFactory，改变的只是数据源类型，PooledDataSourceFactory对应的数据源为PooledDataSource，而UnpooledDataSourceFactory对应的为，UnpooledDataSource。[/color]