使用JPA实现分页和模糊查询

1、首先创建DAO层接口，实现JpaRepository和JpaSpecificationExecutor两个接口

• JpaRepository<SysOperLog, Integer> 泛型参数分别是：要查询的实体（Entity），实体的主键类型
• JpaSpecificationExecutor<SysOperLog> 泛型参数：要查的实体

@Repository
public interface SysOperLogRepository extends JpaRepository<SysOperLog, Integer>, JpaSpecificationExecutor<SysOperLog> {

}

2、Service层进行查询操作

分页模糊查询三步骤：

• 创建查询条件对象
• 创建分页对象
• 进行查询操作

/**
     * 分页查找SysOperLog
     *
     * @param query    查询条件
     * @param pagenum  页码
     * @param pageSize 每页显示的数据
     * @return
     */
	public Page<SysOperLog> pageQueryListLikeOperDesc(String query, Integer pageNo, Integer pageSize) {
		// 查询条件存在这个对象中
		Specification<SysOperLog> specification = new Specification<SysOperLog>() {
			// 重新Specification的toPredicate方法
			public Predicate toPredicate(Root<SysOperLog> root, CriteriaQuery<?> criteriaQuery,
					CriteriaBuilder criteriaBuilder) {
				// 我要模糊查询的字段是adminName
				Path operDesc = root.get("operDesc");
				// criteriaBuilder.like模糊查询，第一个参数是上一行的返回值，第二个参数是like('%xxx%')中，xxx的值
				Predicate predicate = criteriaBuilder.like(operDesc, "%" + query + "%");
				return predicate;
			}
		};
		//排序
		Sort sort = Sort.by(Sort.Direction.DESC, "id");
		// 分页条件存在这个对象中
		PageRequest pageRequest = PageRequest.of(pageNo - 1, pageSize, sort);
		// 进行查询操作，第一个参数是查询条件对象，第二个参数是分页对象
		Page<SysOperLog> page = sysOperLogRepository.findAll(specification, pageRequest);
		// 返回的数据都封装在了Page<SysOperLog>对象中
		return page;
	}

如果要获得Page对象中的数据，可以直接使用page.getContent();方法

List<SysOperLog> sysOperLogList = page.getContent();

Page对象中封装的数据（下面data中就是page对象的数据）

{
	"success": true,
	"code": 200,
	"message": "OK",
	"data": {
		"content": [{
			"id": 47,
			"operModule": "角色管理",
			"operMethod": "com.laoxu.java.authman.controller.SysRoleController.saveMenu",
			"operType": "修改",
			"operDesc": "分配权限",
			"reqMethod": "POST",
			"operParam": "{roleId:15}\n{menuIds:[1, 3, 10, 11, 4, 14, 8, 9]}\n",
			"operIp": "0:0:0:0:0:0:0:1",
			"operUri": "/authman/sysRole/saveMenu",
			"operUser": "admin",
			"createTime": "2021-04-14 00:31:56"
		}, {
			"id": 46,
			"operModule": "角色管理",
			"operMethod": "com.laoxu.java.authman.controller.SysRoleController.saveMenu",
			"operType": "修改",
			"operDesc": "分配权限",
			"reqMethod": "POST",
			"operParam": "{roleId:15}\n{menuIds:[1, 3, 10, 11, 8, 9]}\n",
			"operIp": "0:0:0:0:0:0:0:1",
			"operUri": "/authman/sysRole/saveMenu",
			"operUser": "admin",
			"createTime": "2021-04-14 00:31:14"
		}, {
			"id": 28,
			"operModule": "部门管理",
			"operMethod": "com.laoxu.java.authman.controller.SysDeptController.remove",
			"operType": "删除",
			"operDesc": "删除部门",
			"reqMethod": "POST",
			"operParam": "{id:19}\n",
			"operIp": "0:0:0:0:0:0:0:1",
			"operUri": "/authman/sysDept/remove",
			"operUser": "admin",
			"createTime": "2021-04-13 23:50:08"
		}],
		"pageable": {
			"sort": {
				"empty": false,
				"sorted": true,
				"unsorted": false
			},
			"offset": 0,
			"pageSize": 20,
			"pageNumber": 0,
			"paged": true,
			"unpaged": false
		},
		"totalElements": 47,
		"totalPages": 3,
		"last": false,
		"number": 0,
		"size": 20,
		"sort": {
			"empty": false,
			"sorted": true,
			"unsorted": false
		},
		"numberOfElements": 20,
		"first": true,
		"empty": false
	}
}