Java如何避免两个返回类型不同的相似方法出现代码重复

首先需要修正两个基础设计问题，再消除方法的代码重复：

• WarehouseSearchFilter子类中重复定义了companyId字段，这会隐藏父类的同名字段，极易引发逻辑错误，建议直接删除子类中的该字段。
• 两个getWarehouseXXXSearchFilter方法逻辑完全一致，仅参数和返回值类型不同，可通过以下两种方式重构消除重复。

方案1：泛型方法重构 #

用泛型限定类型范围，既复用公共逻辑，又保证类型安全：

// 抽取出的泛型公共方法
private <T extends WarehouseSimpleSearchFilter> T getWarehouseSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, T searchFilter) {
    if (CollectionUtils.isEmpty(carrierIds) && CollectionUtils.isEmpty(shipperIds)) {
        // 注意：原代码中存在getCompanyId/getCompanyIds的拼写差异，疑似笔误，请确认统一
        final Set<Long> newCarrierIds = getCompanyIds(WarehousePermission.READ_AVAILABLE, authorization);
        final Set<Long> newShipperIds = getCompanyIds(WarehousePermission.READ_COMPANY, authorization);
        searchFilter.setCarrierIds(newCarrierIds);
        searchFilter.setShipperIds(newShipperIds);
        return searchFilter;
    }
    if (!CollectionUtils.isEmpty(carrierIds)) {
        checkPermission(WarehousePermission.READ_AVAILABLE, authorization);
        searchFilter.setCarrierIds(Collections.unmodifiableSet(carrierIds));
    }
    if (!CollectionUtils.isEmpty(shipperIds)) {
        checkPermission(WarehousePermission.READ_COMPANY, authorization);
        searchFilter.setShipperIds(Collections.unmodifiableSet(shipperIds));
    }
    return searchFilter;
}

// 原方法简化（若不需要保留原方法签名，可直接删除并调用泛型方法）
private WarehouseSimpleSearchFilter getWarehouseSimpleSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, WarehouseSimpleSearchFilter searchFilter) {
    return getWarehouseSearchFilter(carrierIds, shipperIds, authorization, searchFilter);
}

private WarehouseSearchFilter getWarehouseSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, WarehouseSearchFilter searchFilter) {
    return getWarehouseSearchFilter(carrierIds, shipperIds, authorization, searchFilter);
}

方案2：抽公共父类参数方法 #

如果不想使用泛型，可将公共逻辑抽成接收父类类型参数的方法，子类方法调用后强转（因传入的是子类实例，强转安全）：

// 抽取出的公共方法
private WarehouseSimpleSearchFilter fillWarehouseSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, WarehouseSimpleSearchFilter searchFilter) {
    if (CollectionUtils.isEmpty(carrierIds) && CollectionUtils.isEmpty(shipperIds)) {
        final Set<Long> newCarrierIds = getCompanyIds(WarehousePermission.READ_AVAILABLE, authorization);
        final Set<Long> newShipperIds = getCompanyIds(WarehousePermission.READ_COMPANY, authorization);
        searchFilter.setCarrierIds(newCarrierIds);
        searchFilter.setShipperIds(newShipperIds);
        return searchFilter;
    }
    if (!CollectionUtils.isEmpty(carrierIds)) {
        checkPermission(WarehousePermission.READ_AVAILABLE, authorization);
        searchFilter.setCarrierIds(Collections.unmodifiableSet(carrierIds));
    }
    if (!CollectionUtils.isEmpty(shipperIds)) {
        checkPermission(WarehousePermission.READ_COMPANY, authorization);
        searchFilter.setShipperIds(Collections.unmodifiableSet(shipperIds));
    }
    return searchFilter;
}

// 原方法简化
private WarehouseSimpleSearchFilter getWarehouseSimpleSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, WarehouseSimpleSearchFilter searchFilter) {
    return fillWarehouseSearchFilter(carrierIds, shipperIds, authorization, searchFilter);
}

private WarehouseSearchFilter getWarehouseSearchFilter(Set<Long> carrierIds, Set<Long> shipperIds, Authorization authorization, WarehouseSearchFilter searchFilter) {
    return (WarehouseSearchFilter) fillWarehouseSearchFilter(carrierIds, shipperIds, authorization, searchFilter);
}

额外注意事项 #

• 原代码中getWarehouseSimpleSearchFilter内调用的getCompanyId（单数）与另一个方法的getCompanyIds（复数）存在拼写差异，大概率是笔误，需统一为正确的方法名，避免运行时错误。
• 务必删除WarehouseSearchFilter中的companyId字段，否则会出现父类与子类字段隔离的问题，导致数据不一致。

内容的提问来源于stack exchange，提问作者Matexon