mybatis-3.4.6 SQL执行流程

系列

• mybatis-3.4.6 配置介绍
• mybatis-3.4.6 顶层配置解析
• mybatis-3.4.6 子配置解析
• mybatis-3.4.6 mapper解析
• mybatis-3.4.6 SQL执行流程
• mybatis-3.4.6 SqlSession执行过程
• mybatis-3.4.6 缓存介绍
• mybatis-3.4.6 自增主键
• mybatis-3.4.6 foreach 自增主键

开篇

• 这个系列是基于mybatis-3.4.6版本的源码解析，这篇文章是梳理基于SqlSessionFactory的mybatis的整体执行流程，文章更侧重于整体流程的梳理。
• mybatis基于SqlSessionFactory的执行包含四步骤，分别是构建SqlSessionFactory、构建SqlSession对象，获取mapper对象、执行SQL语句。

demo举例

public class MybatisHelloWorld {

    public static void main(String[] args) {

        String resouce = "configuration.xml";
        Reader reader;
        try {
            reader = Resources.getResourceAsReader(resouce);
            // 1、构建SqlSessionFactory对象
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            // 2、构建SqlSession对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            try {
                // 3、获取mapper对象
                UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
                // 4、执行SQL语句
                ImcUser imcUser = userMapper.getById(1,"nick");
                System.out.println("xxxxxx " + imcUser.getUserNick());
            } finally {
                sqlSession.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

• 1、构建SqlSessionFactory对象，其中SqlSessionFactory是根据配置文件build生成。
• 2、构建SqlSession对象，通过sqlSessionFactory.openSession获取SqlSession对象。
• 3、获取mapper对象，通过sqlSession.getMapper获取mapper对象。
• 4、通过mapper的方法执行SQL语句，通过调用mapper的interface对应的方法获取数据。

执行过程分析

执行流程图

mybatis执行流程图

• 整体的执行过程如mybatis执行流程图所示。
• 核心步骤一是返回MapperProxy对象。
• 核心步骤二是通过MapperProxy对象执行execute。
• 核心步骤三是通过MapperMethod来执行请求。

DefaultSqlSessionFactory

public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;

  public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
  }

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

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      // 创建事务相关
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      // 创建executor对象
      final Executor executor = configuration.newExecutor(tx, execType);
      // 核心在于创建DefaultSqlSession对象
      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();
    }
  }
}

• DefaultSqlSessionFactory的openSessionFromDataSource方法负责创建DefaultSqlSession对象。
• DefaultSqlSession对象的变量包括all-in-one的configuration，执行的Executor对象等。

DefaultSqlSession

public class DefaultSqlSession implements SqlSession {

  private final Configuration configuration;
  private final Executor executor;

  private final boolean autoCommit;
  private boolean dirty;
  private List<Cursor<?>> cursorList;

  public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
    this.configuration = configuration;
    this.executor = executor;
    this.dirty = false;
    this.autoCommit = autoCommit;
  }

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

• DefaultSqlSession的目前核心在于根据type返回mapper对象。

getMapper

public class Configuration {

  protected final MapperRegistry mapperRegistry = new MapperRegistry(this);

  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }
}

• Configuration的mapperRegistry维持着mapper和MapperProxyFactory。
• mapperRegistry是整个mapper代理的核心数据结构。

public class MapperRegistry {

  private final Configuration config;
  private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();

  public MapperRegistry(Configuration config) {
    this.config = config;
  }

  @SuppressWarnings("unchecked")
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);

    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

• MapperRegistry通过knownMappers维持mapper类和MapperProxyFactory的映射关系。
• getMapper通过mapperProxyFactory.newInstance来创建代理类。

MapperProxyFactory

public class MapperProxyFactory<T> {

  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();

  public MapperProxyFactory(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class<T> getMapperInterface() {
    return mapperInterface;
  }

  public Map<Method, MapperMethod> getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

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

• MapperProxyFactory的newInstance主要是创建mapper的接口对应的proxy对象MapperProxy。
• newInstance返回是通过jdk的动态代理生成的新对象。

MapperProxy

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    // 通过MapperMethod来执行流程
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }
}

• MapperProxy会新建MapperMethod对象并执行其execute方法。

MapperMethod

public class MapperMethod {

  private final SqlCommand command;
  private final MethodSignature method;

  public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
    this.command = new SqlCommand(config, mapperInterface, method);
    this.method = new MethodSignature(config, mapperInterface, method);
  }

  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;
  }
}

• MapperMethod会创建SqlCommand对象并执行具体的SQL。
• MapperMethod的execute本质上是通过sqlSession实现真正的执行逻辑。

SqlCommand

public class MapperMethod {

  public static class SqlCommand {

    private final String name;
    private final SqlCommandType type;

    public SqlCommand(Configuration configuration, Class<?> mapperInterface, Method method) {
      final String methodName = method.getName();
      final Class<?> declaringClass = method.getDeclaringClass();
      // 解析MappedStatement
      MappedStatement ms = resolveMappedStatement(mapperInterface, methodName, declaringClass,
          configuration);
      if (ms == null) {
        if (method.getAnnotation(Flush.class) != null) {
          name = null;
          type = SqlCommandType.FLUSH;
        } else {
          throw new BindingException("Invalid bound statement (not found): "
              + mapperInterface.getName() + "." + methodName);
        }
      } else {
        name = ms.getId();
        type = ms.getSqlCommandType();
        if (type == SqlCommandType.UNKNOWN) {
          throw new BindingException("Unknown execution method for: " + name);
        }
      }
    }

    public String getName() {
      return name;
    }

    public SqlCommandType getType() {
      return type;
    }

    private MappedStatement resolveMappedStatement(Class<?> mapperInterface, String methodName,
        Class<?> declaringClass, Configuration configuration) {
      String statementId = mapperInterface.getName() + "." + methodName;
      if (configuration.hasStatement(statementId)) {
        return configuration.getMappedStatement(statementId);
      } else if (mapperInterface.equals(declaringClass)) {
        return null;
      }
      for (Class<?> superInterface : mapperInterface.getInterfaces()) {
        if (declaringClass.isAssignableFrom(superInterface)) {
          MappedStatement ms = resolveMappedStatement(superInterface, methodName,
              declaringClass, configuration);
          if (ms != null) {
            return ms;
          }
        }
      }
      return null;
    }
  }
}

• SqlCommand的构造函数会解析MappedStatement对象，根据mapperInterface.getName() + "." + methodName从Configuration的mappedStatements获取mappedStatement对象。
• mappedStatements是在解析mapper的配置文件过程中生成的。
• 本质上SqlCommand的创建过程关联了mapper的Interface和XML的SQL定义。

SqlSessionFactory类关系图

DefaultSqlSessionFactory SqlSession

参考文章

• 源码参考
• mybatis官网介绍
• 深入理解mybatis原理
• Mybatis3.4.x技术内幕
• mybatis 3.x源码深度解析与最佳实践