Ibatis源码分析.doc

读ibatis源码为什么说SqlMapClient是线程安全的Ibatis做为一个半自动化的Orm框架有他的缺点和优点。在这里我就不宽泛的说这些了。就说说为什么SqlMapClient是线程安全的，他是怎么实现的。 提出问题： Java代码 1. privatestaticSqlMapClientsqlMapper;2. 3. /*4. *Itsnotagoodideatoputcodethatcanfailinaclassinitializer,5. *butforsakeofargument,hereshowyouconfigureanSQLMap.6. */7. static8. try9. Readerreader=Resources.getResourceAsReader(com/mydomain/data/SqlMapConfig.xml);10. sqlMapper=SqlMapClientBuilder.buildSqlMapClient(reader);11. reader.close();12. catch(IOExceptione)13. /Failfast.14. thrownewRuntimeException(SomethingbadhappenedwhilebuildingtheSqlMapClientinstance.+e,e);15. 16. private static SqlMapClient sqlMapper; /* * Its not a good idea to put code that can fail in a class initializer, * but for sake of argument, heres how you configure an SQL Map. */ static try Reader reader = Resources.getResourceAsReader(com/mydomain/data/SqlMapConfig.xml); sqlMapper = SqlMapClientBuilder.buildSqlMapClient(reader); reader.close(); catch (IOException e) / Fail fast. throw new RuntimeException(Something bad happened while building the SqlMapClient instance. + e, e); 这是一段ibatis simple工程的代码，大家都能看明白这是一个单例，只有一个SqlMapClient对象存在，在多线程的情况下，SqlMapClient是怎么解决事务隔离呢，怎么共享资源的呢？ 一、 SqlMapClient是怎么被创建的 打开SqlMapClientBuilder发现buildSqlMapClien一句话 Java代码 1. publicstaticSqlMapClientbuildSqlMapClient(Readerreader)2. /returnnewXmlSqlMapClientBuilder().buildSqlMap(reader);3. returnnewSqlMapConfigParser().parse(reader);4. public static SqlMapClient buildSqlMapClient(Reader reader) / return new XmlSqlMapClientBuilder().buildSqlMap(reader); return new SqlMapConfigParser().parse(reader); 我们顺着这条线一路看下去 SqlMapConfigParser类的做了两件事把reader交个一个NodeletParser去解析reader(也就是我们的配置文件)，在一个就是XmlParserState的一个属性产生一个SqlMapClient对象 Java代码 1. publicclassSqlMapConfigParser2. 3. protectedfinalNodeletParserparser=newNodeletParser();4. privateXmlParserStatestate=newXmlParserState();5. publicSqlMapClientparse(Readerreader)6. try7. usingStreams=false;8. 9. parser.parse(reader);10. returnstate.getConfig().getClient();11. catch(Exceptione)12. thrownewRuntimeException(Erroroccurred.Cause:+e,e);13. 14. public class SqlMapConfigParser protected final NodeletParser parser = new NodeletParser(); private XmlParserState state = new XmlParserState();public SqlMapClient parse(Reader reader) try usingStreams = false; parser.parse(reader); return state.getConfig().getClient(); catch (Exception e) throw new RuntimeException(Error occurred. Cause: + e, e); 打开NodeletParser的parse方法，我们发现他就是解析xml配置文件的 Java代码 1. publicvoidparse(Readerreader)throwsNodeletException2. try3. Documentdoc=createDocument(reader);4. parse(doc.getLastChild();5. catch(Exceptione)6. thrownewNodeletException(ErrorparsingXML.Cause:+e,e);7. 8. public void parse(Reader reader) throws NodeletException try Document doc = createDocument(reader); parse(doc.getLastChild(); catch (Exception e) throw new NodeletException(Error parsing XML. Cause: + e, e); 最后这些文件被分门别类的放在了XmlParserState的这些属性里 Java代码 1. privateSqlMapConfigurationconfig=newSqlMapConfiguration();2. 3. privatePropertiesglobalProps=newProperties();4. privatePropertiestxProps=newProperties();5. privatePropertiesdsProps=newProperties();6. privatePropertiescacheProps=newProperties();7. privatebooleanuseStatementNamespaces=false;8. privateMapsqlIncludes=newHashMap();9. 10. privateParameterMapConfigparamConfig;11. privateResultMapConfigresultConfig;12. privateCacheModelConfigcacheConfig;13. 14. privateStringnamespace;15. privateDataSourcedataSource;private SqlMapConfiguration config = new SqlMapConfiguration(); private Properties globalProps = new Properties(); private Properties txProps = new Properties(); private Properties dsProps = new Properties(); private Properties cacheProps = new Properties(); private boolean useStatementNamespaces = false; private Map sqlIncludes = new HashMap(); private ParameterMapConfig paramConfig; private ResultMapConfig resultConfig; private CacheModelConfig cacheConfig; private String namespace;private DataSource dataSource;现在我们回过头看return state.getConfig().getClient(); 是这句话获得了SqlMapClient对象，这个对象是怎么创建的呢，在SqlMapConfiguration的构造方法里面就已经创建好了。 Java代码 1. publicSqlMapConfiguration()2. errorContext=newErrorContext();3. delegate=newSqlMapExecutorDelegate();4. typeHandlerFactory=delegate.getTypeHandlerFactory();5. client=newSqlMapClientImpl(delegate);6. registerDefaultTypeAliases();7. public SqlMapConfiguration() errorContext = new ErrorContext(); delegate = new SqlMapExecutorDelegate(); typeHandlerFactory = delegate.getTypeHandlerFactory(); client = new SqlMapClientImpl(delegate); registerDefaultTypeAliases(); 原来我们的到的并不是SqlMapClient(接口不能实现)对象，而是他的一个实现SqlMapClientImpl 二、 深入SqlMapClientImpl内部 SqlMapClientImpl类中只有三个字段 Java代码 1. privatestaticfinalLoglog=LogFactory.getLog(SqlMapClientImpl.class);2. 3. publicSqlMapExecutorDelegatedelegate;4. 5. protectedThreadLocallocalSqlMapSession=newThreadLocal(); private static final Log log = LogFactory.getLog(SqlMapClientImpl.class);public SqlMapExecutorDelegate delegate;protected ThreadLocal localSqlMapSession = new ThreadLocal();log是一个日志记录的对象，与线程安全肯定是无关的 SqlMapExecutorDelegate这个类里面有什么东西呢 Java代码 1. privatestaticfinalProbePROBE=ProbeFactory.getProbe();2. 3. privatebooleanlazyLoadingEnabled;4. privatebooleancacheModelsEnabled;5. privatebooleanenhancementEnabled;6. privatebooleanuseColumnLabel=true;7. privatebooleanforceMultipleResultSetSupport;8. 9. privateTransactionManagertxManager;10. 11. privateHashMapmappedStatements;12. privateHashMapcacheModels;13. privateHashMapresultMaps;14. privateHashMapparameterMaps;15. 16. protectedSqlExecutorsqlExecutor;17. privateTypeHandlerFactorytypeHandlerFactory;18. privateDataExchangeFactorydataExchangeFactory;19. 20. privateResultObjectFactoryresultObjectFactory;21. privatebooleanstatementCacheEnabled;private static final Probe PROBE = ProbeFactory.getProbe(); private boolean lazyLoadingEnabled; private boolean cacheModelsEnabled; private boolean enhancementEnabled; private boolean useColumnLabel = true; private boolean forceMultipleResultSetSupport; private TransactionManager txManager; private HashMap mappedStatements; private HashMap cacheModels; private HashMap resultMaps; private HashMap parameterMaps; protected SqlExecutor sqlExecutor; private TypeHandlerFactory typeHandlerFactory; private DataExchangeFactory dataExchangeFactory; private ResultObjectFactory resultObjectFactory; private boolean statementCacheEnabled;这些属性都是一些关于跟sqlMap配置的一些信息，这些信息和线程安全也没有很大的关系。 最后就剩下localSqlMapSession字段了，其实有经验的同学一眼就能看出来这点的，ThreadLocal就是为处理线程安全而来 的，他的实质为每个线程保存一个副本。他的实现就是存在一个全局的Map存放localSqlMapSession，key是线程的id号value值是 一个localSqlMapSession的副本。 SqlMapClientImpl里面的方法： Java代码 1. publicObjectinsert(Stringid,Objectparam)throwsSQLException2. returngetLocalSqlMapSession().insert(id,param);3. 4. 5. publicObjectinsert(Stringid)throwsSQLException6. returngetLocalSqlMapSession().insert(id);7. 8. 9. publicintupdate(Stringid,Objectparam)throwsSQLException10. returngetLocalSqlMapSession().update(id,param);11. 12. 13. publicintupdate(Stringid)throwsSQLException14. returngetLocalSqlMapSession().update(id);15. 16. 17. publicintdelete(Stringid,Objectparam)throwsSQLException18. returngetLocalSqlMapSession().delete(id,param);19. 20. 21. publicintdelete(Stringid)throwsSQLException22. returngetLocalSqlMapSession().delete(id);23. 24. 25. publicObjectqueryForObject(Stringid,ObjectparamObject)throwsSQLException26. returngetLocalSqlMapSession().queryForObject(id,paramObject);27. public Object insert(String id, Object param) throws SQLException return getLocalSqlMapSession().insert(id, param); public Object insert(String id) throws SQLException return getLocalSqlMapSession().insert(id); public int update(String id, Object param) throws SQLException return getLocalSqlMapSession().update(id, param); public int update(String id) throws SQLException return getLocalSqlMapSession().update(id); public int delete(String id, Object param) throws SQLException return getLocalSqlMapSession().delete(id, param); public int delete(String id) throws SQLException return getLocalSqlMapSession().delete(id); public Object queryForObject(String id, Object paramObject) throws SQLException return getLocalSqlMapSession().queryForObject(id, paramObject); 多么熟悉的方法啊，这就是我们经常用的curd的方法。从代码上证明了我们的推测，线程安全就是和localSqlMapSession有关 虽然找到了相关的属性，但是他们是怎么实现的呢。 三、 线程安全的实现。 就dao部分的线程安全来说一个是主要是事务的完成性。如果事务能够保证完整性，那么就可以说是线程安全的。 localSqlMapSession存的是什么什么东西呢，我们打开代码看看。 Java代码 1. protectedSqlMapSessionImplgetLocalSqlMapSession()2. SqlMapSessionImplsqlMapSession=(SqlMapSessionImpl)localSqlMapSession.get();3. if(sqlMapSession=null|sqlMapSession.isClosed()4. sqlMapSession=newSqlMapSessionImpl(this);5. localSqlMapSession.set(sqlMapSession);6. 7. returnsqlMapSession;8. protected SqlMapSessionImpl getLocalSqlMapSession() SqlMapSessionImpl sqlMapSession = (SqlMapSessionImpl) localSqlMapSession.get(); if (sqlMapSession = null | sqlMapSession.isClosed() sqlMapSession = new SqlMapSessionImpl(this); localSqlMapSession.set(sqlMapSession); return sqlMapSession; 再研究一下SqlMapSessionImpl，这个类只有三个字段 protected SqlMapExecutorDelegate delegate; protected SessionScope sessionScope; protected boolean closed; 很明显SessionScope这是我们要找的东西 Java代码 1. privatestaticlongnextId;2. privatelongid;3. /UsedbyAny4. privateSqlMapClientsqlMapClient;5. privateSqlMapExecutorsqlMapExecutor;6. privateSqlMapTransactionManagersqlMapTxMgr;7. privateintrequestStackDepth;8. /UsedbyTransactionManager9. privateTransactiontransaction;10. privateTransactionStatetransactionState;11. /UsedbySqlMapExecutorDelegate.setUserProvidedTransaction()12. privateTransactionStatesavedTransactionState;13. /UsedbyStandardSqlMapClientandGeneralStatement14. privatebooleaninBatch;15. /UsedbySqlExecutor16. privateObjectbatch;17. privatebooleancommitRequired;18. privateMappreparedStatements;private static long nextId; private long id; / Used by Any private SqlMapClient sqlMapClient; private SqlMapExecutor sqlMapExecutor; private SqlMapTransactionManager sqlMapTxMgr; private int requestStackDepth; / Used by TransactionManager private Transaction transaction; private TransactionState transactionState; / Used by SqlMapExecutorDelegate.setUserProvidedTransaction() private TransactionState savedTransactionState; / Used by StandardSqlMapClient and GeneralStatement private boolean inBatch; / Used by SqlExecutor private Object batch; private boolean commitRequired; private Map preparedStatements;根据我们的分析事务的完整性足以保证dao层的线程安全。Transaction保存在ThreadLocal里面证明了SqlMapClient是线程安全的，我们在整个工程中只要一个SqlMapClient对象就够了。 再来看下SessionScope这个类的字段 private SqlMapClient sqlMapClient;保存的是一个SqlMapClient private SqlMapExecutor sqlMapExecutor; 执行sql用的 private SqlMapTransactionManager sqlMapTxMgr; 管理事务的 private int requestStackDepth; / Used by TransactionManager private Transaction transaction; 事务 private TransactionState transactionState; 事务的状态 / Used by SqlMapExecutorDelegate.setUserProvidedTransaction() private TransactionState savedTransactionState; 事务的保存状态 / Used by StandardSqlMapClient and GeneralStatement private boolean inBatch;是否批处理 / Used by SqlExecutor private Object batch; private boolean commitRequired;是否用提交 private Map preparedStatements;这个应该是保存批处理的PreparedStatement 我们突然发现没有连接类Connection，如果用jdbc的话Connection是多么重要的一个对象啊，在这里没有保存Connection呢。打开JdbcTransaction(一个Transaction的实现) Java代码 1. privatestaticfinalLogconnectionLog=LogFactory.getLog(Connection.class);2. 3. privateDataSourcedataSource;4. privateConnectionconnection;5. privateIsolationLevelisolationLevel=newIsolationLevel();6. 7. publicJdbcTransaction(DataSourceds,intisolationLevel)throwsTransactionException8. /CheckParameters9. dataSource=ds;10. if(dataSource=null)11. thrownewTransactionException(JdbcTransactioninitializationfailed.DataSourcewasnull.);12. 13. this.isolationLevel.setIsolationLevel(isolationLevel);14. 15. 16. privatevoidinit()throwsSQLException,TransactionException17. /OpenJDBCTransaction18. connection=dataSource.getConnection();19. if(connection=null)20. thrownewTransactionException(JdbcTransactioncouldnotstarttransaction.Cause:TheDataSourcereturnedanullconnection.);21. 22. /IsolationLevel23. isolationLevel.applyIsolationLevel(connection);24. /AutoCommit25. if(connection.getAutoCommit()26. connection.setAutoCommit(false);27. 28. /Debug29. if(connectionLog.isDebugEnabled()30. connection=ConnectionLogProxy.newInstance(connection);31. 32. 33. 34. publicvoidcommit()throwsSQLException,TransactionException35. if(connection!=null)36. mit();37. 38. 39. 40. publicvoidrollback()throwsSQLException,TransactionException41. if(connection!=null)42. connection.rollback();43. 44. 45. 46. publicvoidclose()throwsSQLException,TransactionException47. if(connection!=null)48. try49. isolationLevel.restoreIsolationLevel(connection);50. finally51. connection.close();52. connection=null;53. 54. 55. 56. 57. publicConnectiongetConnection()throwsSQLException,TransactionException58. if(connection=null)59. init();60. 61. returnconnection;62. private static final Log connectionLog = LogFactory.getLog(Connection.class); private DataSource dataSource; private Connection connection; private IsolationLevel isolationLevel = new IsolationLevel(); public JdbcTransaction(DataSource ds, int isolationLevel) throws TransactionException / Check Parameters dataSource = ds; if (dataSource = null) throw new TransactionException(JdbcTransaction