Java实现List中的数据分类（使用JDK1.8的List的stream()方法进行优化）

蔚落 2023-06-06 03:45 24阅读 0赞

##### 背景 #####

1.  JDK1.8实现List中的数据分类。
2.  在JDK1.8之前是没有提供这样的API的，实现过程如下：[JDK1.8之前实现List中的数据分类][JDK1.8_List]或者[使用guava实现List分类数据][guava_List]

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##### 过程 #####

1.  场景：需要把考生按照考生所属机构进行分类处理。已知考生在一个List容器中，并且考生有所属机构。
2.  Candidate类

public class Candidate {
        private String orgId;//我的目的是以这个orgId分类
        private String orgName;
        private String candidateId;
    
        public Candidate(){
    
        }
    
        public Candidate(String orgId, String candidateId, String orgName) {
            super();
            this.candidateId = candidateId;
            this.orgId = orgId;
            this.orgName = orgName;
        }
    
    
        public String getCandidateId() {
            return candidateId;
        }
    
        public void setCandidateId(String candidateId) {
            this.candidateId = candidateId;
        }
    
        public String getOrgId() {
            return orgId;
        }
    
        public void setOrgId(String orgId) {
            this.orgId = orgId;
        }
    
        public String getOrgName() {
            return orgName;
        }
    
        public void setOrgName(String orgName) {
            this.orgName = orgName;
    
        }
    }

1.  CandidateOrg类

public class CandidateOrg {
        private String orgId;
        private String orgName;
    
        public CandidateOrg() {
    
        }
    
        public CandidateOrg(String orgId, String orgName) {
            super();
            this.orgId = orgId;
            this.orgName = orgName;
        }
    
        public String getOrgId() {
            return orgId;
        }
    
        public void setOrgId(String orgId) {
            this.orgId = orgId;
        }
    
        public String getOrgName() {
            return orgName;
        }
    
        public void setOrgName(String orgName) {
            this.orgName = orgName;
        }
    }

1.  测试类

public class ClassificationTest {
        public static void main(String[] args) {
            List<Candidate> list = new ArrayList<Candidate>();
            list.add(new Candidate("1","1","机构一"));//机构id,考生id，机构名称。
            list.add(new Candidate("1","2","机构一"));
            list.add(new Candidate("2","3","机构二"));
            list.add(new Candidate("2","4","机构二"));
            list.add(new Candidate("3","5","机构三"));
            list.add(new Candidate("3","6","机构三"));
            list.add(new Candidate("4","7","机构四"));
            list.add(new Candidate("4","8","机构四"));
    
            Map<String, List<Candidate>> map = list.stream().collect(Collectors.groupingBy(
                    Candidate::getOrgId));
    
        }
    }

1.  结果（内存快照）  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L291dHNhbmRpbmc_size_16_color_FFFFFF_t_70]

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##### 小结 #####

1.  在JDK1.8之前确实没有找到一个好的实现方式。

[JDK1.8_List]: https://blog.csdn.net/outsanding/article/details/79460541
[guava_List]: https://blog.csdn.net/outsanding/article/details/102470402
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L291dHNhbmRpbmc_size_16_color_FFFFFF_t_70]: /images/20230601/fb3a769978a14115ae93be29fb0dfd18.png