大后端-番外篇-01 Java 常用方法总结
一、集合遍历
集合遍历有多种方法，一种是 foreach遍历，另一个是直接使用 map 遍历，一般高逼端的程序员都使用map遍历。
map集合遍历
@Override
public void saveImages(Long id, List<String> images){
if(images == null || images.size() == 0 || id < 0){
}else{
List<SpuImagesEntity> collect = images.stream().map(img ->{
SpuImagesEntity spuImagesEntity = new SpuImagesEntity();
spuImagesEntity.setId(id);
spuImagesEntity.setImgUrl(img);
return spuImagesEntity;
}).collect(Collectors.toList());
this.saveBatch(collect);
}
}二、对象属性赋值
获取一个对象，需要把这个对象的值复制到另外一个实体对象类，那木，如果两者的属性字段一样，则可以使用 BeanUtils.copyProperties(vo,infoEntity); 方法来处理，而不用一个一个做映射对照set来处理。
/**
* //TODO 高级部分完善
* @param vo
*/
@Transactional
@Override
public void saveSpuInfo(SpuSaveVo vo) {
//1、保存spu基本信息 pms_spu_info
SpuInfoEntity infoEntity = new SpuInfoEntity();
// 复制vo的属性字段值到 infoEntity对象
BeanUtils.copyProperties(vo,infoEntity);
infoEntity.setCreateTime(new Date());
infoEntity.setUpdateTime(new Date());
this.saveBaseSpuInfo(infoEntity);
}三、集合过滤
List<ProductAttrValueEntity> baseAttrs = attrValueService.baseAttrlistforspu(spuId);
Set<Long> idSet = new HashSet<>(searchAttrIds);
baseAttrs.stream().filter(item ->{
return idSet.contains(item.getAttrId());
}).collect(Collectors.toList());四、集合先过滤然后再遍历处理
先对每个数据进行过滤，然后在对每个数据进行封装，最后再收集起来，这个是更高级的用法：
List<ProductAttrValueEntity> baseAttrs = attrValueService.baseAttrlistforspu(spuId);
List<SkuEsModel.Attrs> attrsList = baseAttrs.stream().filter(item ->{
return idSet.contains(item.getAttrId());
}).map(item->{
SkuEsModel.Attrs attrs1 = new SkuEsModel.Attrs();
BeanUtils.copyProperties(item, attrs1);
return attrs1;
}).collect(Collectors.toList());五、集合混合处理
Stream在java中我们经常称为『流』，我们会用流去对集合进行一些流水线的操作，stream就像工厂一样，我们只需要把集合和命令还有一些参数灌输到流水线中去，最终加工成我们想要的结果。
原集合 —> 流 —> 各种操作(过滤、分组、统计) —> 终端操作Stream流的操作流程一般都是这样的，先将集合转为流，然后经过各种操作，比如过滤、筛选、分组、计算。最后的终端操作，就是转化成我们想要的数据，一般还是集合，有的时候我们想变成count计数，后面我们会一一举例
示例：
package com.base.labguage.java8;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class StreamMap {
private static class People{
private String name;
private Integer age;
private String address;
// 只给出构造方法，忽略get/set细节
public People(String name, Integer age, String address) {
this.name = name;
this.age = age;
this.address = address;
}
}
public static class PeoplePub{
private String name;
private Integer age;
// 只给出构造方法，忽略get/set细节
public PeoplePub(String name, Integer age) {
this.name = name;
this.age = age;
}
// 重写toString方法
public String toString(){
return "(" + this.name + "," + this.age + ")";
}
}
public static void main(String[] args) {
List<People> peoples = Arrays.asList(
new People("zs", 25, "cs"),
new People("ls", 28, "bj"),
new People("ww", 23, "nj")
);
// List -> String
List<String> names = peoples.stream().map(p -> p.getName()).collect(Collectors.toList());
// stream流实现英文字母转大写
List<String> upNames = names.stream().map(String::toUpperCase).collect(Collectors.toList());
// stream流实现数字乘倍数
List<Integer> ages = peoples.stream().map(p -> p.getAge() * 2).collect(Collectors.toList());
// list - > new List
List<PeoplePub> peoplePubs = peoples.stream().map(p -> {
return new PeoplePub(p.getName(), p.getAge());
}).collect(Collectors.toList());
System.out.println("to print upnames List : " + upNames);
System.out.println("to print ages List : " + ages);
System.out.println("to print new people List" + peoplePubs.toString());
}
}
项目实战代码：
gulimall-product/src/main/java/com/atguigu/gulimall/product/service/impl/CategoryServiceImpl.java
@Override
public Map<String, List<Catelog2Vo>> getCatalogJson() {
// 1、查出所有1级分类
List<CategoryEntity> level1Categorys = getLevel1Categorys();
// 2、封装数据
Map<String, List<Catelog2Vo>> parent_cid = level1Categorys.stream().collect(Collectors.toMap(k->k.getCatId().toString(),
v->{
// 每一个的一级分类，查到这个一级分类的二级分类
List<CategoryEntity> categoryEntities = baseMapper.selectList(new QueryWrapper<CategoryEntity>().eq("parent_cid", v.getCatId()));
// 封装上面的结果
List<Catelog2Vo> catelog2Vos = null;
if(categoryEntities != null){
catelog2Vos = categoryEntities.stream().map(l2 ->{
Catelog2Vo catelog2Vo = new Catelog2Vo(v.getCatId().toString(), null, l2.getCatId().toString(), l2.getName());
// 找二级分类的三级分类
List<CategoryEntity> level3Catelog = baseMapper.selectList(new QueryWrapper<CategoryEntity>().eq("parent_cid", l2.getCatId()));
if(level3Catelog != null){
List<Catelog2Vo.Catelog3Vo> catelog3vos = level3Catelog.stream().map(l3 ->{
// 封装成指定格式
Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo(l2.getCatId().toString(), l3.getCatId().toString(), l3.getName());
return catelog3Vo;
}).collect(Collectors.toList());
catelog2Vo.setCatalog3List(catelog3vos);
}
return catelog2Vo;
}).collect(Collectors.toList());
}
return catelog2Vos;
}));
return parent_cid;
}返回响应结果结构：
[
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "1",
"id": "1",
"name": "电子书"
},
{
"catalog2Id": "1",
"id": "2",
"name": "网络原创"
},
{
"catalog2Id": "1",
"id": "3",
"name": "数字杂志"
},
{
"catalog2Id": "1",
"id": "4",
"name": "多媒体图书"
}
],
"id": "1",
"name": "电子书刊"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "2",
"id": "5",
"name": "音乐"
},
{
"catalog2Id": "2",
"id": "6",
"name": "影视"
},
{
"catalog2Id": "2",
"id": "7",
"name": "教育音像"
}
],
"id": "2",
"name": "音像"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "3",
"id": "8",
"name": "少儿"
},
{
"catalog2Id": "3",
"id": "9",
"name": "商务投资"
},
{
"catalog2Id": "3",
"id": "10",
"name": "英语学习与考试"
},
{
"catalog2Id": "3",
"id": "11",
"name": "文学"
},
{
"catalog2Id": "3",
"id": "12",
"name": "传记"
},
{
"catalog2Id": "3",
"id": "13",
"name": "励志"
}
],
"id": "3",
"name": "英文原版"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "4",
"id": "14",
"name": "小说"
},
{
"catalog2Id": "4",
"id": "15",
"name": "文学"
},
{
"catalog2Id": "4",
"id": "16",
"name": "青春文学"
},
{
"catalog2Id": "4",
"id": "17",
"name": "传记"
},
{
"catalog2Id": "4",
"id": "18",
"name": "艺术"
}
],
"id": "4",
"name": "文艺"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "5",
"id": "19",
"name": "少儿"
},
{
"catalog2Id": "5",
"id": "20",
"name": "0-2岁"
},
{
"catalog2Id": "5",
"id": "21",
"name": "3-6岁"
},
{
"catalog2Id": "5",
"id": "22",
"name": "7-10岁"
},
{
"catalog2Id": "5",
"id": "23",
"name": "11-14岁"
}
],
"id": "5",
"name": "少儿"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "6",
"id": "24",
"name": "历史"
},
{
"catalog2Id": "6",
"id": "25",
"name": "哲学"
},
{
"catalog2Id": "6",
"id": "26",
"name": "国学"
},
{
"catalog2Id": "6",
"id": "27",
"name": "政治/军事"
},
{
"catalog2Id": "6",
"id": "28",
"name": "法律"
},
{
"catalog2Id": "6",
"id": "29",
"name": "人文社科"
},
{
"catalog2Id": "6",
"id": "30",
"name": "心理学"
},
{
"catalog2Id": "6",
"id": "31",
"name": "文化"
},
{
"catalog2Id": "6",
"id": "32",
"name": "社会科学"
}
],
"id": "6",
"name": "人文社科"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "7",
"id": "33",
"name": "经济"
},
{
"catalog2Id": "7",
"id": "34",
"name": "金融与投资"
},
{
"catalog2Id": "7",
"id": "35",
"name": "管理"
},
{
"catalog2Id": "7",
"id": "36",
"name": "励志与成功"
}
],
"id": "7",
"name": "经管励志"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "8",
"id": "37",
"name": "生活"
},
{
"catalog2Id": "8",
"id": "38",
"name": "健身与保健"
},
{
"catalog2Id": "8",
"id": "39",
"name": "家庭与育儿"
},
{
"catalog2Id": "8",
"id": "40",
"name": "旅游"
},
{
"catalog2Id": "8",
"id": "41",
"name": "烹饪美食"
}
],
"id": "8",
"name": "生活"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "9",
"id": "42",
"name": "工业技术"
},
{
"catalog2Id": "9",
"id": "43",
"name": "科普读物"
},
{
"catalog2Id": "9",
"id": "44",
"name": "建筑"
},
{
"catalog2Id": "9",
"id": "45",
"name": "医学"
},
{
"catalog2Id": "9",
"id": "46",
"name": "科学与自然"
},
{
"catalog2Id": "9",
"id": "47",
"name": "计算机与互联网"
},
{
"catalog2Id": "9",
"id": "48",
"name": "电子通信"
}
],
"id": "9",
"name": "科技"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "10",
"id": "49",
"name": "中小学教辅"
},
{
"catalog2Id": "10",
"id": "50",
"name": "教育与考试"
},
{
"catalog2Id": "10",
"id": "51",
"name": "外语学习"
},
{
"catalog2Id": "10",
"id": "52",
"name": "大中专教材"
},
{
"catalog2Id": "10",
"id": "53",
"name": "字典词典"
}
],
"id": "10",
"name": "教育"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "11",
"id": "54",
"name": "艺术/设计/收藏"
},
{
"catalog2Id": "11",
"id": "55",
"name": "经济管理"
},
{
"catalog2Id": "11",
"id": "56",
"name": "文化/学术"
},
{
"catalog2Id": "11",
"id": "57",
"name": "少儿"
}
],
"id": "11",
"name": "港台图书"
},
{
"catalog1Id": "1",
"catalog3List": [
{
"catalog2Id": "12",
"id": "58",
"name": "工具书"
},
{
"catalog2Id": "12",
"id": "59",
"name": "杂志/期刊"
},
{
"catalog2Id": "12",
"id": "60",
"name": "套装书"
}
],
"id": "12",
"name": "其他"
}
]六、使用IDEA抽取方法
有时候代码的一个方法中写了很多不同的业务，导致整个方法代码量很多，很难查看，这个时候就需要人工将部分逻辑抽出来，直接封装一个方法，然后在这个方法中调用即可，可以大大提高代码的可读性。以前笨办法是直接复制上边的代码到一个新方法中，现在可以使用IDEA功能直接抽取方法。
业务代码：
@Override
public Map<String, List<Catelog2Vo>> getCatalogJson() {
// 将数据库的多次查询变为一次
List<CategoryEntity> selectList = baseMapper.selectList(null);
// 1、查出所有1级分类
List<CategoryEntity> level1Categorys = getLevel1Categorys();
// 2、封装数据
Map<String, List<Catelog2Vo>> parent_cid = level1Categorys.stream().collect(Collectors.toMap(k->k.getCatId().toString(),
v->{
// 每一个的一级分类，查到这个一级分类的二级分类
List<CategoryEntity> categoryEntities = baseMapper.selectList(new QueryWrapper<CategoryEntity>().eq("parent_cid", v.getCatId()));
// 封装上面的结果
List<Catelog2Vo> catelog2Vos = null;
if(categoryEntities != null){
catelog2Vos = categoryEntities.stream().map(l2 ->{
Catelog2Vo catelog2Vo = new Catelog2Vo(v.getCatId().toString(), null, l2.getCatId().toString(), l2.getName());
// 找二级分类的三级分类
List<CategoryEntity> level3Catelog = baseMapper.selectList(new QueryWrapper<CategoryEntity>().eq("parent_cid", l2.getCatId()));
if(level3Catelog != null){
List<Catelog2Vo.Catelog3Vo> catelog3vos = level3Catelog.stream().map(l3 ->{
// 封装成指定格式
Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo(l2.getCatId().toString(), l3.getCatId().toString(), l3.getName());
return catelog3Vo;
}).collect(Collectors.toList());
catelog2Vo.setCatalog3List(catelog3vos);
}
return catelog2Vo;
}).collect(Collectors.toList());
}
return catelog2Vos;
}));
return parent_cid;
}
抽取方法步骤：
自动替换之后的方法：
@Override
public Map<String, List<Catelog2Vo>> getCatalogJson() {
// 将数据库的多次查询变为一次
List<CategoryEntity> selectList = baseMapper.selectList(null);
// 1、查出所有1级分类
List<CategoryEntity> level1Categorys = getLevel1Categorys();
// 2、封装数据
Map<String, List<Catelog2Vo>> parent_cid = level1Categorys.stream().collect(Collectors.toMap(k->k.getCatId().toString(),
v->{
// 每一个的一级分类，查到这个一级分类的二级分类
List<CategoryEntity> categoryEntities = getParent_cid(v);
// 封装上面的结果
List<Catelog2Vo> catelog2Vos = null;
if(categoryEntities != null){
catelog2Vos = categoryEntities.stream().map(l2 ->{
Catelog2Vo catelog2Vo = new Catelog2Vo(v.getCatId().toString(), null, l2.getCatId().toString(), l2.getName());
// 找二级分类的三级分类
List<CategoryEntity> level3Catelog = getParent_cid(l2);
if(level3Catelog != null){
List<Catelog2Vo.Catelog3Vo> catelog3vos = level3Catelog.stream().map(l3 ->{
// 封装成指定格式
Catelog2Vo.Catelog3Vo catelog3Vo = new Catelog2Vo.Catelog3Vo(l2.getCatId().toString(), l3.getCatId().toString(), l3.getName());
return catelog3Vo;
}).collect(Collectors.toList());
catelog2Vo.setCatalog3List(catelog3vos);
}
return catelog2Vo;
}).collect(Collectors.toList());
}
return catelog2Vos;
}));
return parent_cid;
}
private List<CategoryEntity> getParent_cid(CategoryEntity v) {
return baseMapper.selectList(new QueryWrapper<CategoryEntity>().eq("parent_cid", v.getCatId()));
}是不是很强大呢？减少了自己很多的工作量。
七、Mybatis-plus相关
查询条件语句够时间：
@Override
public List<SkuImagesEntity> getImagesBySkuId(Long skuId) {
// 构建查询条件
QueryWrapper<SkuImagesEntity> queryWrapper = new QueryWrapper<SkuImagesEntity>().eq("sku_id", skuId);
// 查询
List<SkuImagesEntity> imgs = this.baseMapper.selectList(queryWrapper);
return imgs;
}为者常成，行者常至
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