[Java] Make a unique list of objects

Problem
I am using do query to retrieve a List of Cam101wGridData data. The data contains user name and email address. 
User asks to remove duplicate email address from the data list, how to do it?

1	List<Cam101wGridData> result= doQuery(form, result);

How-To
Steps are as following:
Step1. Create a Cam101wEmailCsvBean and override equals and hashCode methods (using email attribute)

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package x.x.x.model; import java.io.Serializable; import lombok.AllArgsConstructor; import lombok.Data; import lombok.EqualsAndHashCode; import lombok.NoArgsConstructor; /** * Mail格式下載 bean (解決 Email 重複的資料) * * Any class definition may be annotated with @EqualsAndHashCode to let lombok generate * implementations of the equals(Object other) and hashCode() methods. By default, it'll use all * non-static, non-transient fields, but you can exclude more fields by naming them in the optional * exclude parameter to the annotation. Alternatively, you can specify exactly which fields you wish * to be used by naming them in the of parameter. */ @AllArgsConstructor @NoArgsConstructor @Data @EqualsAndHashCode(of = "email") public class Cam101wEmailCsvBean implements Serializable { private static final long serialVersionUID = 1L; /** * 會員姓名 */ private String userName; /** * E-Mail */ private String email; }

Step2. Convert from List<Cam101wGridData>  to List<Cam101wEmailCsvBean>:

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/** * 將 List<Cam101wGridData> 轉成 List<Cam101wEmailCsvBean>. * * @param result List<Cam101wGridData> * @return List<Cam101wEmailCsvBean> */ private List<Cam101wEmailCsvBean> convertToCam101wEmailCsvBean(List<Cam101wGridData> result) { List<Cam101wEmailCsvBean> emailCsvBeans = new ArrayList<>(); if (CollectionUtils.isNotEmpty(result)) { for (Cam101wGridData row : result) { Cam101wEmailCsvBean emailBean = new Cam101wEmailCsvBean(row.getUserName(), row.getEmail()); emailCsvBeans.add(emailBean); } } return emailCsvBeans; }

Step3. Convert List to Set (remove duplicate email), and convert Set to List 

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private List<Cam101wEmailCsvBean> getDistinctEmailCsvBean(List<Cam101wEmailCsvBean> emailCsvBeans) { List<Cam101wEmailCsvBean> distinctEmailCsvBeans = new ArrayList<>(); Set<Cam101wEmailCsvBean> emailCsvSet = new HashSet<>(emailCsvBeans); distinctEmailCsvBeans.addAll(emailCsvSet); return distinctEmailCsvBeans; }

Code snippet (Before and after)

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// before (with duplicate emails) List<Cam101wGridData> result= doQuery(form, result); // after (with distinct email) List<Cam101wGridData> result= doQuery(form, result); List<Cam101wEmailCsvBean> emailCsvBeans = convertToCam101wEmailCsvBean(result); List<Cam101wEmailCsvBean> distinctEmailCsvBeans = getDistinctEmailCsvBean(emailCsvBeans);

Reference
[1] https://projectlombok.org/features/EqualsAndHashCode.html    
[2] https://stackoverflow.com/questions/20126470/java-how-to-keep-unique-values-in-a-list-of-objects