<settings>
    <!--开启全局延迟加载功能-->
    <setting name="lazyLoadingEnabled" value="true"/>
</settings>

<!-- 开启⼀对多 延迟加载 -->
<resultMap id="userMap" type="user">
    <id column="id" property="id"></id>
    <result column="username" property="username"></result>
    <result column="password" property="password"></result>
    <result column="birthday" property="birthday"></result>
<!--
fetchType="lazy" 懒加载策略
fetchType="eager" ⽴即加载策略
-->
    <collection property="orderList" ofType="order" column="id"
        select="com.lagou.dao.OrderMapper.findByUid" fetchType="lazy">
    </collection>
</resultMap>
<select id="findAll" resultMap="userMap">
    SELECT * FROM `user`
</select>

public class Configuration {
        /**
         * aggressiveLazyLoading：
         * 当开启时，任何⽅法的调⽤都会加载该对象的所有属性。否则，每个属性会按需加载（参考lazyLoadTriggerMethods).
         * 默认为true
         */
        protected boolean aggressiveLazyLoading;
        /**
         * 延迟加载触发⽅法
         */
        protected Set<String> lazyLoadTriggerMethods = new HashSet<String>(Arrays.asList(new String[]{"equals", "clone", "hashCode", "toString" }));
        /**
         * 是否开启延迟加载
         */
        protected boolean lazyLoadingEnabled = false;
 
        /**
         * 默认使⽤Javassist代理⼯⼚
         *
         * @param proxyFactory
         */
        public void setProxyFactory(ProxyFactory proxyFactory) {
            if (proxyFactory == null) {
                proxyFactory = new JavassistProxyFactory();
            }
            this.proxyFactory = proxyFactory;
        }
        //省略...
    }

// 创建映射后的结果对象
    private Object createResultObject(ResultSetWrapper rsw, ResultMap resultMap, ResultLoaderMap lazyLoader, String columnPrefix) throws SQLException {
        // useConstructorMappings ，表示是否使用构造方法创建该结果对象。此处将其重置
        this.useConstructorMappings = false; // reset previous mapping result
        final List<Class<?>> constructorArgTypes = new ArrayList<>(); // 记录使用的构造方法的参数类型的数组
        final List<Object> constructorArgs = new ArrayList<>(); // 记录使用的构造方法的参数值的数组
        // 创建映射后的结果对象
        Object resultObject = createResultObject(rsw, resultMap, constructorArgTypes, constructorArgs, columnPrefix);
        if (resultObject != null && !hasTypeHandlerForResultObject(rsw, resultMap.getType())) {
            // 如果有内嵌的查询，并且开启延迟加载，则创建结果对象的代理对象
            final List<ResultMapping> propertyMappings = resultMap.getPropertyResultMappings();
            for (ResultMapping propertyMapping : propertyMappings) {
                // issue gcode #109 && issue #149
                if (propertyMapping.getNestedQueryId() != null && propertyMapping.isLazy()) {
               // 创建延迟加载代理对象
                    resultObject = configuration.getProxyFactory().createProxy(resultObject, lazyLoader, configuration, objectFactory, constructorArgTypes, constructorArgs);
                    break;
                }
            }
        }
        // 判断是否使用构造方法创建该结果对象
        this.useConstructorMappings = resultObject != null && !constructorArgTypes.isEmpty(); // set current mapping result
        return resultObject;
    }