Spring boot JPA实现分页和枚举转换代码示例

1.实现分页

方法一：使用Pageable

使用Pageable作为入参传入Repository，返回值用Page<T>接收

UserRepository

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> { }

UserServiceImpl

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; ​ /** * 查询用户列表 */ @Override public Page<User> queryAll(Pageable pageable) { return userRepository.findAll(pageable); } ​ }

UserService

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 { /** * 查询用户列表 */ Page<User> queryAll(Pageable pageable); }

Controller

/** * 查询用户列表 */ @GetMapping('/userList') public Page<User> queryAll(){ //注意，前端页面的页面是从1开始，而JPA是从0开始 Pageable pageable = PageRequest.of(0,5); //查询用户列表 return userService.queryAll(pageable); }

方法二：以元模型概念为基础的Criteria 查询方法

UserRepository额外继承JpaSpecificationExecutor<>

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> { }

UserServiceImpl

/** * 查询用户列表 */ @Override public Page<User> queryAll(String name,String age,Pageable pageable) { Specification<User> specification = (Specification<User>)(root, query, criteriaBuilder) ->{ List<Predicate> list = new ArrayList<>(); // 第一个name为User实体对象中的字段，第二个name为参数 Predicate p1 = criteriaBuilder.equal(root.get('name'),name); list.add(p1); //if (!age.equals(null)) { // // 此处为查询serverName中含有age的数据 // Predicate p2 = criteriaBuilder.like(root.get('age'),'%'+age+'%' ); // list.add(p2); //} return criteriaBuilder.and(list.toArray(new Predicate[0])); }; return userRepository.findAll(specification,pageable); }

其它代码如方法一，不用动。

2.枚举转换

**方法一：实体类加@Enumerated注解

package com.kinglead.demo.enums;import com.fasterxml.jackson.annotation.JsonValue;public interface BaseEnum<K> { /** * 真正与数据库进行映射的值 * * @return */ K getCode(); /** * 显示的信息 * * @return */ @JsonValue //jackson返回报文response的设置 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 //无参构造函数 @AllArgsConstructor //所以参数构造函数 @Entity //声明为JPA实体 @Table(name = 't_user') //该标注与@Entity标注并列使用，用于指明数据库的表名 public class User implements Serializable { private static final long serialVersionUID = -21070736985722463L; ​ @Id //指明主键 @GeneratedValue(strategy= GenerationType.AUTO) private Long id; ​ @Column(name = 'name', columnDefinition = '姓名') //指明字段 private String name; ​ @Column(name = 'age', columnDefinition = '年龄') //指明字段 private Long age; ​ @Column(name = 'email', columnDefinition = '邮箱') //指明字段 private String email; ​ @Column(name = 'gender', columnDefinition = '性别') //指明字段 @Enumerated(EnumType.STRING) private GenderEnum gender; ​ }

方法二：使用jpa2.1规范里面的属性转换器

将方法一中实体对象User的gender成员变量上的注解@Enumerated(EnumType.STRING)去掉

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); } }

上面的转换器只是针对某一种枚举进行转换，如果写成通用的转换器呢，后续研究

源码地址：https://github.com/kinglead2012/myblog

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