mybatis工作流程

基本使用方法

// 擷取mybatis配置檔案
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
// 建立SqlSessionFactory建立器
SqlSessionFactoryBuilder sfb =  new SqlSessionFactoryBuilder();
// 通過SqlSessionFactoryBuilder 建立SqlSessionFactory ，并傳入配置檔案流
SqlSessionFactory ssf= sfb.build(is);
// 通過工廠擷取sqlSession
SqlSession sqlSession = ssf.openSession();
// sqlSession擷取mapper
DatasourceMapper mapper = sqlSession.getMapper(xxxMapper.class);
// 在通過mapper調用相關方法
String s = mapper.getXxx();
System.out.println(s);
           

解析

SqlSessionFactoryBuilder sfb = new SqlSessionFactoryBuilder();

SqlSessionFactory ssf= sfb.build(is);

public SqlSessionFactory build(InputStream inputStream) {
  	return build(inputStream, null, null);
}

public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
    	// xml解析器
      	XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      	// parser.parse() 擷取配置檔案資訊，并封裝成Configuration對象
      	return build(parser.parse());
    } catch (Exception e) {
      	throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
   		ErrorContext.instance().reset();
	    try {
	      reader.close();
	    } catch (IOException e) {
	      // Intentionally ignore. Prefer previous error.
	    }
    }
}

public SqlSessionFactory build(Configuration config) {
	return new DefaultSqlSessionFactory(config);
}
// DefaultSqlSessionFactory 是 SqlSessionFactory的一個實作類
public DefaultSqlSessionFactory(Configuration configuration) {
	this.configuration = configuration;
}
           

SqlSession sqlSession = ssf.openSession();

public SqlSession openSession() {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}

/**
 * @Param execType   執行器 預設SIMPLE （SIMPLE, REUSE, BATCH）
 * @Param level      事務等級	
 * @Param autoCommit 自動送出事務 false
 */
private SqlSession openSessionFromDataSource(ExecutorType execType, 
						TransactionIsolationLevel level, 	
						boolean autoCommit) {
    Transaction tx = null;
    try {
    	// 通過配置檔案中的<Encironment>标簽中的資料，擷取資料庫配置資訊。
	    final Environment environment = configuration.getEnvironment();
	    // 通過environment中建立事務工廠
	    final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
	    // 通過事務工廠建立事務 【資料源，資料庫隔離等級，是否自動送出】
	    tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
	    // 建立執行器 相當于JDBC中的statement
	    final Executor executor = configuration.newExecutor(tx, execType);
	    // 傳回SqlSession
	    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();
    }
}

           

DatasourceMapper mapper = sqlSession.getMapper(xxxMapper.class);

<T> T getMapper(Class<T> type);

@Override
public <T> T getMapper(Class<T> type) {
  	return getConfiguration().getMapper(type, this);
}

// 實際上就是通過 mapperRegistry 幫我們存儲了所有的mapper對象，mapperRegistry 底層封裝了HashMap。
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
	// private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<>();
	// 
	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);
	}
}

// class MapperProxyFactory<T>
public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
}

// 類下的成員變量
// private final Class<T> mapperInterface;
// private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap<>();
protected T newInstance(MapperProxy<T> mapperProxy) {
	// JDK 動态代理
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
           

String s = mapper.getXxx();

其實是通過調用

MapperProxy

的invoke方法。

public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable {
    return mapperMethod.execute(sqlSession, args);
}
           

execute

方法

public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    switch (command.getType()) {
      case INSERT: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.insert(command.getName(), param));
        break;
      }
      case UPDATE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.update(command.getName(), param));
        break;
      }
      case DELETE: {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = rowCountResult(sqlSession.delete(command.getName(), param));
        break;
      }
      case SELECT:
        if (method.returnsVoid() && method.hasResultHandler()) {
          executeWithResultHandler(sqlSession, args);
          result = null;
        } else if (method.returnsMany()) {
          result = executeForMany(sqlSession, args);
        } else if (method.returnsMap()) {
          result = executeForMap(sqlSession, args);
        } else if (method.returnsCursor()) {
          result = executeForCursor(sqlSession, args);
        } else {
          Object param = method.convertArgsToSqlCommandParam(args);
          result = sqlSession.selectOne(command.getName(), param);
          if (method.returnsOptional()
              && (result == null || !method.getReturnType().equals(result.getClass()))) {
            result = Optional.ofNullable(result);
          }
        }
        break;
      case FLUSH:
        result = sqlSession.flushStatements();
        break;
      default:
        throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method '" + command.getName()
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

           

查詢流程

public <E> List<E> query(MappedStatement ms, Object parameterObject,
 			RowBounds rowBounds, ResultHandler resultHandler,
 			CacheKey key, BoundSql boundSql)
    throws SQLException {
    // 從二級緩存中擷取
  Cache cache = ms.getCache();
  // 如果有 則從緩存中取
  if (cache != null) {
    flushCacheIfRequired(ms);
    if (ms.isUseCache() && resultHandler == null) {
      ensureNoOutParams(ms, boundSql);
      @SuppressWarnings("unchecked")
      List<E> list = (List<E>) tcm.getObject(cache, key);
      if (list == null) {
        list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
        tcm.putObject(cache, key, list); // issue #578 and #116
      }
      return list;
    }
  }
  // 查詢一級緩存
  return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
}
           

總結

• 擷取配置檔案，轉成流。(

  InputStream is = Resources.getResourceAsStream("mybatis-config.xml")

  )
• 解析流得到 configuration
• 通過SqlSessionFactoryBuilder 建立 SqlSessionFactory
• 通過SqlSessionFactory 擷取 SqlSession
• 使用SqlSession 執行SQL (MapperProxy)
• CachingExecutor 判斷是否開啟二級緩存
  • 如果沒有開啟二級緩存，則調用 BaseExecutor 調用一級緩存
  • 如果一級緩存有，則傳回，否則，請往下
• RountingStatementHandle 選中sql執行方式
• 選則預編譯方式，PreparedStatementHandle
• 最後，通過DefaultResultSetHandle傳回結果。

參考：https://blog.csdn.net/qq_38270106/article/details/93398694