Mybatis系列之二 Mapper对象获取

一、思路

1. Mybatis Mapper对象获取过程分析;
2. MapperProxy怎么执行sql
3. SqlSession的生命周期?
4. SqlSession如何和Mapper对象绑定?
5. Spring怎么管理mybatis的事务呢?

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二、Mybatis Mapper对象获取过程分析;

重点关注mybatis和spring结合后是怎么获取mapper对象;根据下面的BPMN图来看源码;

MapperProxy获取过程.jpg

a.
关注MapperFactoryBean这个类，

  @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }

SqlSessionTemplate

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

Configuration

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

MapperRegistry

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

MapperProxyFactory

@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);
  }

三、MapperProxy怎么执行sql

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;

  // ... 省略部分内容

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }

    // 执行真正的sql方法
    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;
  }

}

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未完待续 ...