MyBatis-获取 xxxMapper（源码）

Main 方法，mybatis 版本为 3.5.0

使用 MapperProxyFactory 创建一个 MapperProxy 的代理对象

代理对象里面包含了 DefaultSqlSession（Executor）

InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
session = sqlSessionFactory.openSession();
DeptMapper mapper = session.getMapper(DeptMapper.class);

session.getMapper(DeptMapper.class)

org.apache.ibatis.session.defaults.DefaultSqlSession

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

configuration.<T>getMapper(type, this)

org.apache.ibatis.session.Configuration

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

mapperRegistry.getMapper(type, sqlSession)

org.apache.ibatis.binding.MapperRegistry

// 返回代理类
@SuppressWarnings("unchecked")
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.newInstance(sqlSession)

org.apache.ibatis.binding.MapperProxyFactory

@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {
    // 用JDK自带的动态代理生成映射器
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}

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

new MapperProxy<>(sqlSession, mapperInterface, methodCache)

org.apache.ibatis.binding.MapperProxy

/**
 * 映射器代理
 */
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 {
            // 代理以后，所有 Mapper 的方法调用时，都会调用这个 invoke 方法
            // 并不是任何一个方法都需要执行调用代理对象进行执行，如果这个方法是 Object 中通用的方法（toString、hashCode等）则无需执行
            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);
        }
        // 去缓存中找 MapperMethod
        final MapperMethod mapperMethod = cachedMapperMethod(method);
        // 执行
        return mapperMethod.execute(sqlSession, args);
    }

    // 去缓存中找 MapperMethod
    private MapperMethod cachedMapperMethod(Method method) {
        return methodCache.computeIfAbsent(method, k -> new MapperMethod(mapperInterface, method, sqlSession.getConfiguration()));
    }

    private Object invokeDefaultMethod(Object proxy, Method method, Object[] args) throws Throwable {
        final Constructor<MethodHandles.Lookup> constructor = MethodHandles.Lookup.class.getDeclaredConstructor(Class.class, int.class);
        if (!constructor.isAccessible()) {
            constructor.setAccessible(true);
        }
        final Class<?> declaringClass = method.getDeclaringClass();
        return constructor
                .newInstance(declaringClass, MethodHandles.Lookup.PRIVATE | MethodHandles.Lookup.PROTECTED | MethodHandles.Lookup.PACKAGE | MethodHandles.Lookup.PUBLIC)
                .unreflectSpecial(method, declaringClass).bindTo(proxy).invokeWithArguments(args);
    }

    /**
     * Backport of java.lang.reflect.Method#isDefault()
     */
    private boolean isDefaultMethod(Method method) {
        return (method.getModifiers() & (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC)) == Modifier.PUBLIC && method.getDeclaringClass().isInterface();
    }
}

时序图

---

https://github.com/tuguangquan/mybatis/tree/master/src/main/java/org/apache/ibatis