详解MyBatis延迟加载是如何实现的

<settings>
    <!-- 开启全局的延迟加载 -->
    <setting name="lazyLoadingEnabled" value="true"/>
    <!-- 将积极加载改为消极加载（即延迟加载） -->
    <setting name="aggressiveLazyLoading" value="false"/>
    <!-- 当开启延迟加载时，每个属性都会延迟加载 -->
    <setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/>
</settings>

<resultMap id="blogResultMap" type="Blog">
    <collection property="posts" ofType="Post" select="selectPostsForBlog" column="id" fetchType="lazy"/>
</resultMap>

<select id="selectBlog" resultMap="blogResultMap">
    SELECT * FROM blog WHERE id = #{id}
</select>

<select id="selectPostsForBlog" parameterType="int" resultType="Post">
    SELECT * FROM post WHERE blog_id = #{id}
</select>

public class LazyLoadingProxy implements InvocationHandler {
    private Object target;
    private boolean loaded;

    public LazyLoadingProxy(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (!loaded && isLoadMethod(method)) {
            loadObject();
            loaded = true;
        }
        return method.invoke(target, args);
    }

    private boolean isLoadMethod(Method method) {
        // 判断方法是否触发加载
        return "getPosts".equals(method.getName());
    }

    private void loadObject() {
        // 执行加载逻辑，比如执行SQL查询
    }
}