package com.kinglead.demo.dao;
 ​
 import com.kinglead.demo.entity.User;
 import org.springframework.data.jpa.repository.JpaRepository;
 ​
 public interface UserRepository extends JpaRepository<User, Long> {
 }

package com.kinglead.demo.service.impl;
 ​
 import com.kinglead.demo.dao.UserRepository;
 import com.kinglead.demo.entity.User;
 import com.kinglead.demo.service.UserService;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Service;
 ​
 import javax.annotation.Resource;
 ​
 @Service
 public class UserServiceImpl implements UserService {
 ​
   @Resource
   private UserRepository userRepository;
 ​
   /**
   * 查詢用戶列表
   */
   @Override
   public Page<User> queryAll(Pageable pageable) {
     return userRepository.findAll(pageable);
   }
 ​
 }

package com.kinglead.demo.service;
 ​
 import com.kinglead.demo.entity.User;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 ​
 import java.util.List;
 import java.util.Map;
 ​
 public interface UserService {
   /**
   * 查詢用戶列表
   */
   Page<User> queryAll(Pageable pageable);
 }

/**
 * 查詢用戶列表
 */
 @GetMapping("/userList")
 public Page<User> queryAll(){
   //注意，前端頁面的頁面是從1開始，而JPA是從0開始
   Pageable pageable = PageRequest.of(0,5);
   //查詢用戶列表
   return userService.queryAll(pageable);
 }

package com.kinglead.demo.dao;
 ​
 import com.kinglead.demo.entity.User;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
 ​
 public interface UserRepository extends JpaRepository<User, Long>, JpaSpecificationExecutor<User> {
 }

/**
   * 查詢用戶列表
   */
   @Override
   public Page<User> queryAll(String name,String age,Pageable pageable) {
       Specification<User> specification = (Specification<User>)(root, query, criteriaBuilder) ->{
         List<Predicate> list = new ArrayList<>();
         // 第一個name為User實體對象中的字段，第二個name為參數(shù)
         Predicate p1 = criteriaBuilder.equal(root.get("name"),name);
         list.add(p1);
 //        if (!age.equals(null)) {
 //          // 此處為查詢serverName中含有age的數(shù)據(jù)
 //          Predicate p2 = criteriaBuilder.like(root.get("age"),"%"+age+"%" );
 //          list.add(p2);
 //        }
         return criteriaBuilder.and(list.toArray(new Predicate[0]));
       };
       return userRepository.findAll(specification,pageable);
   }

package com.kinglead.demo.enums;

import com.fasterxml.jackson.annotation.JsonValue;

public interface BaseEnum<K> {

  /**
   * 真正與數(shù)據(jù)庫進行映射的值
   *
   * @return
   */
  K getCode();

  /**
   * 顯示的信息
   *
   * @return
   */
  @JsonValue //jackson返回報文response的設置
  String getDisplayName();
}

package com.kinglead.demo.enums;
 ​
 public enum GenderEnum implements BaseEnum<String> {
 ​
   MALE("MALE","男"),
   FEMALE("FEMALE","女");
 ​
 ​
   private final String code;
   private final String displayName;
 ​
   GenderEnum(String code, String displayName) {
     this.code = code;
     this.displayName = displayName;
   }
 ​
   @Override
   public String getCode() {
     return code;
   }
 ​
   @Override
   public String getDisplayName() {
     return displayName;
   }}

package com.kinglead.demo.entity;
 ​
 import com.kinglead.demo.enums.GenderEnum;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NoArgsConstructor;
 ​
 import javax.persistence.*;
 import java.io.Serializable;
 ​
 @Data //添加getter、setter方法
 @NoArgsConstructor  //無參構造函數(shù)
 @AllArgsConstructor //所以參數(shù)構造函數(shù)
 @Entity //聲明為JPA實體
 @Table(name = "t_user") //該標注與@Entity標注并列使用，用于指明數(shù)據(jù)庫的表名
 public class User implements Serializable {
   private static final long serialVersionUID = -21070736985722463L;
 ​
   @Id //指明主鍵
   @GeneratedValue(strategy= GenerationType.AUTO)
   private Long id;
 ​
   @Column(name = "name", columnDefinition = "姓名") //指明字段
   private String name;
 ​
   @Column(name = "age", columnDefinition = "年齡") //指明字段
   private Long age;
 ​
   @Column(name = "email", columnDefinition = "郵箱") //指明字段
   private String email;
 ​
   @Column(name = "gender", columnDefinition = "性別") //指明字段
   @Enumerated(EnumType.STRING)
   private GenderEnum gender;
 ​
 }

package com.kinglead.demo.config;
 ​
 import com.kinglead.demo.enums.GenderEnum;
 ​
 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;
 ​
 @Converter(autoApply = true)
 public class ColorConverter implements AttributeConverter<GenderEnum,String> {
 ​
   @Override
   public String convertToDatabaseColumn(GenderEnum attribute) {
     return attribute.getCode();
   }
 ​
   @Override
   public GenderEnum convertToEntityAttribute(String dbData) {
     return GenderEnum.valueOf(dbData);
   }
 }