不能对JPaspecificationExecutor存储库使用findAll（规范，可分页）方法？

Question

无法对JpaSpecificationExecutor存储库使用findAll（规范，分页）方法。我将存储库接口设置为：

package com.task.task.repository;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.stereotype.Repository;

import com.task.task.domain.Employee;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long>, JpaSpecificationExecutor<Employee> {
}

每当我调用EmployeeRepository.findall（规范，分页）时；抛出此错误：

    "error": "Internal Server Error",
    "exception": "org.springframework.beans.BeanInstantiationException",
    "message": "Failed to instantiate [org.springframework.data.jpa.domain.Specifications]: No default constructor found;
nested exception is java.lang.NoSuchMethodException: org.springframework.data.jpa.domain.Specifications.<init>()",
    "path": "/api/task/employee"

这是StackTrace：

2018-01-17 14:41:29.816 ERROR 12132 --- [nio-8080-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.data.jpa.domain.Specifications]: No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.data.jpa.domain.Specifications.<init>()] with root cause

java.lang.NoSuchMethodException: org.springframework.data.jpa.domain.Specifications.<init>()
        at java.lang.Class.getConstructor0(Class.java:3082) ~[na:1.8.0_144]
        at java.lang.Class.getDeclaredConstructor(Class.java:2178) ~[na:1.8.0_144]
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:102) ~[spring-beans-4.3.13.RELEASE.jar:4.3.13.RELEASE]

完整代码：https://github.com/sanketkd/specificationexecutor

@Entity
@Table(name = "emp111")
public class Employee {

  @Id
  @Column(name = "employee_id")
  private Long employeeId;

  @Column(name = "ename", length = 20)
  private String ename;

  @Column(name = "hire_date")
  private Date hireDate;

  @Column(name = "salary")
  private Long salary;

  @Column(name = "skills", length = 30)
  private String skills;

// getters setters

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specifications;
import org.springframework.stereotype.Service;

import com.task.task.domain.Employee;
import com.task.task.repository.EmployeeRepository;

@Service
public class EmployeeService {

  private final EmployeeRepository employeeRepository;

  @Autowired
  public EmployeeService(EmployeeRepository employeeRepository) {
    this.employeeRepository = employeeRepository;
  }

  public Employee getEmployee(Long employeeId) {
    return employeeRepository.findOne(employeeId);
  }

  public Page<Employee> getEmployees(Specifications<Employee> specifications, Pageable pageable) {
    return employeeRepository.findAll(specifications, pageable);
  }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.domain.Specifications;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import com.task.task.domain.Employee;
import com.task.task.service.EmployeeService;

@RestController
@RequestMapping("api/task/employee")
public class EmployeeController {

  private final EmployeeService employeeService;

  @Autowired
  public EmployeeController(EmployeeService employeeService) {
    this.employeeService = employeeService;
  }

  @RequestMapping(method = RequestMethod.GET, path = "/{employeeId:[0-9]\\d*}")
  public Employee getEmployee(@PathVariable Long employeeId) {
    return this.employeeService.getEmployee(employeeId);
  }

  @RequestMapping(method = RequestMethod.GET)
  public Page<Employee> getEmployees(Specifications<Employee> specifications, Pageable pageable) {
    return this.employeeService.getEmployees(specifications, pageable);
  }
}

存储库：

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.stereotype.Repository;

import com.task.task.domain.Employee;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Long>, JpaSpecificationExecutor<Employee> {
}

Answer 1

您得到的异常与存储库无关，这是因为您在控制器中映射了specification 。这是不可能的，因为Spring不知道如何将传入的请求“解析”到specification 。它将尝试通过调用默认构造函数来构造规范，但是由于没有默认构造函数，它将抛出一个异常。

您需要使用适当的请求体（或参数），并在控制器或服务中创建规范而不是将其映射到控制器中。

使用Spring Boot2.x.x，您可以通过以下方式完成：

@RequestMapping(method = RequestMethod.GET)
public Page<Employee> getEmployees(
        // Just plain parameters
        @RequestParam String name,
        @RequestParam int page,
        @ResuestParam int limit) {
    // Creating the specification
    Specification<Employee> spec = Specification.where(EmployeeSpecs.employeeName(name));
    // Creating the Pageable as well
    Pageable pageable = PageRequest.of(page, limit);
    return this.employeeService.getEmployees(specifications, pageable);
}

使用Spring Boot1.x.x，specification.where()称为specifications.where()。此外，PageRequest.of(..)静态方法不存在，您应该使用New PageRequest(..)构造函数。