Mybatis的Environment解析詳解

今天來具體看一下如何解析environments 
//XMLConfigBuilder 

Java代碼  

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();
        //遍歷environments的child節點environment，並解析
            do
            {
                if(!i$.hasNext())
                    break;
                XNode child = (XNode)i$.next();
                String id = child.getStringAttribute("id");
        //如果environment的id屬性，與environments的default相同時，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的構造，啓動有JDBC，POOLED類型的映射關係，這個在解析environment節點時，需要用到下載 

Java代碼  

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

Java代碼  

public Configuration()
    {
        safeRowBoundsEnabled = false;
        safeResultHandlerEnabled = true;
        mapUnderscoreToCamelCase = false;
        aggressiveLazyLoading = true;
        multipleResultSetsEnabled = true;
        useGeneratedKeys = false;//允許JDBC支持生成的鍵
        useColumnLabel = true;
        cacheEnabled = true;//全局的映射器啓用或禁用緩存
        callSettersOnNulls = false;
        localCacheScope = LocalCacheScope.SESSION;//本地一級緩存作用域
        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();//默認ObjectFactory
        objectWrapperFactory = new DefaultObjectWrapperFactory();//默認DefaultObjectWrapperFactory
        mapperRegistry = new MapperRegistry(this);
        lazyLoadingEnabled = false;
        interceptorChain = new InterceptorChain();//插件鏈
        typeHandlerRegistry = new TypeHandlerRegistry();//類型處理註冊器
        typeAliasRegistry = new TypeAliasRegistry();//類型別名註冊器
        languageRegistry = new LanguageDriverRegistry();
    //mappedStatements Map
        mappedStatements = new StrictMap("Mapped Statements collection");
    //mappedStatements，method，二級緩存
        caches = new StrictMap("Caches collection");
    //MapperInterface 方法返回結果類型Map
        resultMaps = new StrictMap("Result Maps collection");
        //MapperInterface 方法參數類型Map
        parameterMaps = new StrictMap("Parameter Maps collection");
    //主鍵生成器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");
    //未解析處理的statements
        incompleteStatements = new LinkedList();
    //未解析處理的CacheRefs
        incompleteCacheRefs = new LinkedList();
    //未解析處理的ResultMaps
        incompleteResultMaps = new LinkedList();
    //未解析處理的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);
    }

從上可以看出JDBC，POOLED類型別名的映射關係如下： 
JDBC，JdbcTransactionFactory 下載
POOLED，PooledDataSourceFactory 

Java代碼  

<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>

Java代碼  

private TransactionFactory transactionManagerElement(XNode context)
        throws Exception
    {
        if(context != null)
        {
            String type = context.getStringAttribute("type");
            Properties props = context.getChildrenAsProperties();
        //從類型解決器中，獲取type對應的類型的實例，從上面的配置來看
        //實際爲JdbcTransactionFactory
            TransactionFactory factory = (TransactionFactory)resolveClass(type).newInstance();
        //設置JdbcTransactionFactory屬性
            factory.setProperties(props);
            return factory;
        } else
        {
            throw new BuilderException("Environment declaration requires a TransactionFactory.");
        }
    }

//JdbcTransactionFactory 

Java代碼  下載

public class JdbcTransactionFactory
    implements TransactionFactory
{
    public void setProperties(Properties properties)
    {
    }
   //根據數據連接新建事務
    public Transaction newTransaction(Connection conn)
    {
        return new JdbcTransaction(conn);
    }
    //根據數據源和事務級別和是否自動提交，新建事務
    public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit)
    {
        return new JdbcTransaction(ds, level, autoCommit);
    }
}

//TransactionFactory 

Java代碼  

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);
}

現在來看一下jdbc事務 

Java代碼  下載

public class JdbcTransaction
    implements Transaction
{
    private static final Log log = LogFactory.getLog(org/apache/ibatis/transaction/jdbc/JdbcTransaction);
    protected Connection connection;//數據庫連接
    protected DataSource dataSource;//數據源
    protected TransactionIsolationLevel level;//事務級別
    protected boolean autoCommmit;//自動提交屬性

    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());
        }
    }
    //獲取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 

Java代碼  

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;
}

從上面可以看出jdbc對應的事務工廠爲JdbcTransactionFactory，由JdbcTransactionFactory，根據數據源，事務級別以及自動提交屬性來，創建JdbcTransaction，而JdbcTransaction的事務管理，是通過數據連接connection，而connection是從datasource獲取，JdbcTransaction的事務管理，就是依靠相應的數據庫driver，來管理，實際依賴於數據庫。 下載

//解析dataSource 

Java代碼  

private DataSourceFactory dataSourceElement(XNode context)
        throws Exception
    {
        if(context != null)
        {
        //獲取數據源的類型，和屬性
            String type = context.getStringAttribute("type");
            Properties props = context.getChildrenAsProperties();
        //根據type從configuration的類型處理器，獲取具體的DataSourceFactory
        //從上文，我們看一看到type爲POOLED，對應的是PooledDataSourceFactory
            DataSourceFactory factory = (DataSourceFactory)resolveClass(type).newInstance();
            factory.setProperties(props);
            return factory;
        } else
        {
            throw new BuilderException("Environment declaration requires a DataSourceFactory.");
        }
    }

// PooledDataSourceFactory 

Java代碼  

public class PooledDataSourceFactory extends UnpooledDataSourceFactory
{

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