高效 告别996，开启java高效编程之门 3-17实战案例预定义收集器

1　　　　重点：

1.1　　Collectors方法之 流转集合，分组，分区的案例应用

 

2　　　　demo之流转集合（toCollectors）：

demo：

/**
     * toList
     * 案例1：流转换为集合
     * 注意：可以用Collectors.toList /toSet/ toMap 等转换成不同的集合
     * */
    @Test
    public void toListTest(){
        List<Sku> list = CartService.getSkuList();
        List<Sku> list2 = list.stream().filter(Sku->Sku.getTotalPrice()>1000).collect(Collectors.toList());
        System.out.println(JSONObject.toJSONString(list2,true));
    }

打印日志：

[
    {
        "skuCategory":"SPROTS",
        "skuId":2020007,
        "skuName":"杠铃",
        "skuPrice":2000.0,
        "totalNum":1,
        "totalPrice":2000.0
    },
    {
        "skuCategory":"ELECTRONICS",
        "skuId":2020008,
        "skuName":"ThinkPad",
        "skuPrice":5000.0,
        "totalNum":1,
        "totalPrice":5000.0
    }
]

Process finished with exit code 0

3　　　　demo之分组（groupingBy）：

demo：

  /**
     * groupingBy
     * 案例2：根据产品种类分组
     * 注意：map的定义
     */
    @Test
    public void groupTest(){
        List<Sku> list = CartService.getSkuList();
        Map<Object,List<Sku>> map = list.stream().collect(Collectors.groupingBy(Sku::getSkuCategory));
        System.out.println(JSONObject.toJSONString(map,true));
    }

打印日志：

{"CLOTHING":[
        {
            "skuCategory":"CLOTHING",
            "skuId":2020002,
            "skuName":"T-shirt",
            "skuPrice":50.0,
            "totalNum":2,
            "totalPrice":100.0
        },
        {
            "skuCategory":"CLOTHING",
            "skuId":2020006,
            "skuName":"大头皮鞋",
            "skuPrice":300.0,
            "totalNum":1,
            "totalPrice":300.0
        }
    ],"BOOKS":[
        {
            "skuCategory":"BOOKS",
            "skuId":2020003,
            "skuName":"人生的枷锁",
            "skuPrice":30.0,
            "totalNum":1,
            "totalPrice":30.0
        },
        {
            "skuCategory":"BOOKS",
            "skuId":2020004,
            "skuName":"老人与海",
            "skuPrice":20.0,
            "totalNum":1,
            "totalPrice":20.0
        },
        {
            "skuCategory":"BOOKS",
            "skuId":2020005,
            "skuName":"剑指高效编程",
            "skuPrice":288.0,
            "totalNum":1,
            "totalPrice":288.0
        }
    ],"SPROTS":[
        {
            "skuCategory":"SPROTS",
            "skuId":2020007,
            "skuName":"杠铃",
            "skuPrice":2000.0,
            "totalNum":1,
            "totalPrice":2000.0
        }
    ],"ELECTRONICS":[
        {
            "skuCategory":"ELECTRONICS",
            "skuId":2020001,
            "skuName":"无人机",
            "skuPrice":999.0,
            "totalNum":1,
            "totalPrice":999.0
        },
        {
            "skuCategory":"ELECTRONICS",
            "skuId":2020008,
            "skuName":"ThinkPad",
            "skuPrice":5000.0,
            "totalNum":1,
            "totalPrice":5000.0
        }
    ]
}

Process finished with exit code 0

4　　　　demo之分区（partitioningBy）：

demo：

@Test
    /**
     * partitioningBy
     * 案例3：根据总价是否大于100进行分区
     * 分区是分组的一种特殊形式，根据特定的条件为true或者为否分为两组
     */
    public void partitioningByTest(){
        List<Sku> list = CartService.getSkuList();
        Map<Boolean,List<Sku>> map = list.stream().collect(Collectors.partitioningBy(Sku->Sku.getTotalPrice()>100));
        System.out.println(JSONObject.toJSONString(map,true));
    }

 

打印日志：

{false:[
        {
            "skuCategory":"CLOTHING",
            "skuId":2020002,
            "skuName":"T-shirt",
            "skuPrice":50.0,
            "totalNum":2,
            "totalPrice":100.0
        },
        {
            "skuCategory":"BOOKS",
            "skuId":2020003,
            "skuName":"人生的枷锁",
            "skuPrice":30.0,
            "totalNum":1,
            "totalPrice":30.0
        },
        {
            "skuCategory":"BOOKS",
            "skuId":2020004,
            "skuName":"老人与海",
            "skuPrice":20.0,
            "totalNum":1,
            "totalPrice":20.0
        }
    ],true:[
        {
            "skuCategory":"ELECTRONICS",
            "skuId":2020001,
            "skuName":"无人机",
            "skuPrice":999.0,
            "totalNum":1,
            "totalPrice":999.0
        },
        {
            "skuCategory":"BOOKS",
            "skuId":2020005,
            "skuName":"剑指高效编程",
            "skuPrice":288.0,
            "totalNum":1,
            "totalPrice":288.0
        },
        {
            "skuCategory":"CLOTHING",
            "skuId":2020006,
            "skuName":"大头皮鞋",
            "skuPrice":300.0,
            "totalNum":1,
            "totalPrice":300.0
        },
        {
            "skuCategory":"SPROTS",
            "skuId":2020007,
            "skuName":"杠铃",
            "skuPrice":2000.0,
            "totalNum":1,
            "totalPrice":2000.0
        },
        {
            "skuCategory":"ELECTRONICS",
            "skuId":2020008,
            "skuName":"ThinkPad",
            "skuPrice":5000.0,
            "totalNum":1,
            "totalPrice":5000.0
        }
    ]
}

Process finished with exit code 0