$ b

findOne 默认为默认值定义为通过一个ID（主键）来加载实体。所以它需要一个 long 或 Long （据我所知）。它采用给定参数（email）的名称，并且正在搜索具有该名称的ID并且根本不会相加。

如果您想通过搜索电子邮件或其他字段已由您定义，您需要使用以下语法：

示例1

搜索范例字段： email

存储库中的方法：
用户findByEmail（字符串电子邮件）

示例2

通过以下方式搜索的示例字段：用户名

存储库中的方法：
用户findByUsername（字符串用户名）

我希望这有助于！

I have searched many pages but didnt found the answer so i paste the whole code.I am testing the testclass and getting the error like "Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Failed to create query for method public abstract org.home.mysystem.entity.User org.home.mysystem.repository.UserRepository.findOne(java.lang.String)! No property findOne found for type User!". Please someone help me

Role.java

package org.home.mysystem.entity;

import java.util.List;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entity
public class Role {

    @Id
    private String name;
    @ManyToMany(mappedBy = "roles")
    private List<User> users;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    public Role(String name, List<User> users) {
        this.name = name;
        this.users = users;
    }

    public Role() {
    }

    public Role(String name) {
        this.name = name;
    }

}

Task.java

package org.home.mysystem.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;

import org.hibernate.validator.constraints.NotEmpty;

@Entity
public class Task {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @NotEmpty
    private String date;
    @NotEmpty
    private String startTime;
    @NotEmpty
    private String stopTime;
    @NotEmpty
    @Column(length=1000)
    private String description;
    @ManyToOne
    @JoinColumn(name="USER_EMAIL")
    private User user;

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getDate() {
        return date;
    }
    public void setDate(String date) {
        this.date = date;
    }
    public String getStartTime() {
        return startTime;
    }
    public void setStartTime(String startTime) {
        this.startTime = startTime;
    }
    public String getStopTime() {
        return stopTime;
    }
    public void setStopTime(String stopTime) {
        this.stopTime = stopTime;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    public Task(String date, String startTime, String stopTime, String description, User user) {
        this.date = date;
        this.startTime = startTime;
        this.stopTime = stopTime;
        this.description = description;
        this.user = user;
    }
    public Task(String date, String startTime, String stopTime, String description) {
        this.date = date;
        this.startTime = startTime;
        this.stopTime = stopTime;
        this.description = description;
    }
    public Task() {
    }



}

User.java

package org.home.mysystem.entity;

import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;
import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.Email;
import org.hibernate.validator.constraints.NotEmpty;

@Entity
public class User {

    @Id
    @Email
    @NotEmpty
    @Column(unique = true)
    private String email;
    @NotEmpty
    private String name;
    @Size(min = 4)
    private String password;
    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
    private List<Task> tasks;

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "USER_ROLES", joinColumns={
            @JoinColumn(name = "USER_EMAIL", referencedColumnName = "email") }, inverseJoinColumns = {
                    @JoinColumn(name = "ROLE_NAME", referencedColumnName = "name") })
    private List<Role> roles;

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public List<Task> gettasks() {
        return tasks;
    }

    public void settasks(List<Task> tasks) {
        this.tasks = tasks;
    }

    public List<Role> getRoles() {
        return roles;
    }

    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }

    public User(String email, String name, String password) {
        this.email = email;
        this.name = name;
        this.password = password;
    }

    public User() {

    }

}

RoleRepository.java

    package org.home.mysystem.repository;

    import org.home.mysystem.entity.Role;
    import org.springframework.data.jpa.repository.JpaRepository;

    public interface RoleRepository extends JpaRepository<Role, String> {

    }

TaskRepository.java

 public interface TaskRepository extends JpaRepository<Task, Long> {

        List<Task> findByUser(User user);

    }

UserRepository.java

package org.home.mysystem.repository;

import org.home.mysystem.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User,String> {

    User findOne(final String email);

}

TaskService.java

 package org.home.mysystem.service;

    import java.util.ArrayList;
    import java.util.List;

    import org.home.mysystem.entity.Role;
    import org.home.mysystem.entity.Task;
    import org.home.mysystem.entity.User;
    import org.home.mysystem.repository.TaskRepository;
    import org.home.mysystem.repository.UserRepository;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
    import org.springframework.stereotype.Service;



    @Service
    public class TaskService {

        @Autowired
        private TaskRepository taskRepository;

        public void addTask(Task task, User user) {
            task.setUser(user);
            taskRepository.save(task);
        }

        public List<Task>  findUserTask(User user){

            return taskRepository.findByUser(user);
        }
    }

UserService.java

import java.util.ArrayList;
import java.util.List;

import org.home.mysystem.entity.Role;
import org.home.mysystem.entity.User;
import org.home.mysystem.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.stereotype.Service;



@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public void createUser(User user) {
        BCryptPasswordEncoder encoder=new BCryptPasswordEncoder();
        user.setPassword(encoder.encode(user.getPassword()));
        Role userRole=new Role("USER");
        List<Role> roles=new ArrayList<>();
        roles.add(userRole);
        user.setRoles(roles);
        userRepository.save(user);
    }

    public void createAdmin(User user) {
        BCryptPasswordEncoder encoder=new BCryptPasswordEncoder();
        user.setPassword(encoder.encode(user.getPassword()));
        Role userRole=new Role("ADMIN");
        List<Role> roles=new ArrayList<>();
        roles.add(userRole);
        user.setRoles(roles);
        userRepository.save(user);
    }

    public User findOne(String email) {
        return userRepository.findOne(email);
    }
}

MyApplicationTest.java

package org.home.mysystem;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;

import java.util.List;

import org.home.mysystem.entity.Task;
import org.home.mysystem.entity.User;
import org.home.mysystem.service.TaskService;
import org.home.mysystem.service.UserService;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MySystemApplicationTests {

    @Autowired
    private UserService userService;

    @Autowired
    private TaskService taskService;

    @Before
    public void initDb() {
      {
          User newUser = new User("testUser@mail.com", "testUser", "123456");
          userService.createUser(newUser); 
      }
      {
          User newUser = new User("testAdmin@mail.com", "testAdmin", "123456");
          userService.createUser(newUser); 
      }

      Task userTask = new Task("03/01/2018", "00:11", "11:00", "You need to work today");
      User user = userService.findOne("testUser@mail.com");
      taskService.addTask(userTask, user);  

    }

    @Test
    public void testUser() {
        User user=userService.findOne("testUser@mail.com");
        assertNotNull(user);
        User admin=userService.findOne("testAdmin@mail.com");
        assertEquals(admin.getEmail(),"testAdmin@mail.com");
    }

    @Test
    public void testTask() {
        User user=userService.findOne("testUser@mail.com");
        List<Task> task=taskService.findUserTask(user);
        assertNotNull(task);
    }

    }

The issue is that Spring is expecting something else as you are giving it.

findOne is by default defined to take an ID (primary key) to load the entity by. So it expects a long or Long (as far as I know). It takes the name of the parameter given (email) and is searching for an ID with that name and that simply doesn't add up.

If you want to search by an email or other field that has been defined by you, you need to use the following syntax:

Example 1

Example field to search by: email

Method in repository: User findByEmail(String email)

Example 2

Example field to search by: username

Method in repository: User findByUsername(String username)

I hope this helps!