Spring Boot调用/users接口遇TemplateInputException错误求助

我是Spring Boot新手，已经实现通过POST方法将HTML页面的用户输入数据插入数据库，但调用GET请求http://localhost:8080/users读取并展示数据时，出现模板解析异常，网页显示500白标错误。

错误日志 #

2023-08-26 12:20:28.125 ERROR 15292 --- [nio-8080-exec-3] org.thymeleaf.TemplateEngine : [THYMELEAF][http-nio-8080-exec-3] Exception processing template "users": Error resolving template [users], template might not exist or might not be accessible by any of the configured Template Resolvers

org.thymeleaf.exceptions.TemplateInputException: Error resolving template [users], template might not exist or might not be accessible by any of the configured Template Resolvers

白标错误页面内容 #

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat Aug 26 12:20:28 IST 2023
There was an unexpected error (type=Internal Server Error, status=500).

相关代码 #

Controller代码 #

package com.forms.demo.htmlExample.controller;


import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;

import com.forms.demo.htmlExample.model.User;
import com.forms.demo.htmlExample.repo.UserRepository;
import com.forms.demo.htmlExample.service.UserService;

@Controller
public class IndexController {
    

    @Autowired
    private UserRepository repo;
    
    @Autowired
    private UserService service;
    
    @GetMapping("/")
    public String index() {
        
        return "index";
    }
    
    @GetMapping("/users")
    public List<User> getUsers() {
        return service.getUsers();
    }
    
    @PostMapping("/register")
    public String userRegistration(@ModelAttribute User user, Model model) {
        
        System.out.println(user.toString());
        
        System.out.println(user.getFname());
        System.out.println(user.getLname());
        System.out.println(user.getEmail());
        System.out.println(user.getGender());
        System.out.println(user.getDob());
        System.out.println(user.getGender());
        model.addAttribute("firstname", user.getFname());
        model.addAttribute("lastname", user.getLname());
        model.addAttribute("email", user.getEmail());
        
        repo.save(user);
        
        model.addAttribute("message", user.getEmail() + " inserted");
        
        return "welcome";
    }
}

Service类代码 #

package com.forms.demo.htmlExample.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.forms.demo.htmlExample.model.User;
import com.forms.demo.htmlExample.repo.UserRepository;

@Service
public class UserService {
    
    @Autowired
    private UserRepository userRepo;
    
    public List<User> getUsers() {
        return userRepo.findAll();
    }
    
}

Repository类代码 #

package com.forms.demo.htmlExample.repo;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.CrudRepository;

import com.forms.demo.htmlExample.model.User;

public interface UserRepository extends JpaRepository<User, Integer> {

}

Entity类代码 #

package com.forms.demo.htmlExample.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="user_data")
public class User {
    
    @Id
    @GeneratedValue
    private int id;
    private String fname;
    private String lname;
    private String email;
    private String passwd;
    private String dob;
    private String gender;

    public String getFname() {
        return fname;
    }
    
    public String getPasswd() {
        return passwd;
    }

    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }

    public void setFname(String fname) {
        this.fname = fname;
    }
    
    public String getLname() {
        return lname;
    }
    
    public void setLname(String lname) {
        this.lname = lname;
    }
    
    public String getEmail() {
        return email;
    }
    
    public void setEmail(String email) {
        this.email = email;
    }
    
    public String getDob() {
        return dob;
    }
    
    public void setDob(String dob) {
        this.dob = dob;
    }
    
    public String getGender() {
        return gender;
    }
    
    public void setGender(String gender) {
        this.gender = gender;
    }   
    
    @Override
    public String toString() {
        return "User [fname=" + fname + ", lname=" + lname + ", email=" + email + ", passwd=" + passwd + ", dob=" + dob
                + ", gender=" + gender + "]";
    }


}

问题原因及解决方法 #

核心问题 #

你的@Controller下的getUsers方法返回List<User>，但Spring Boot默认会尝试用Thymeleaf渲染名为users的模板页面，而你并没有创建对应的users.html模板，因此抛出模板未找到异常。

两种解决方向 #

方向1：返回REST JSON数据（API接口）

如果需求是提供REST API返回用户数据，可将该方法所在的Controller改为@RestController，或在getUsers方法上添加@ResponseBody注解：

// 方案一：改用@RestController
@RestController
public class IndexController {
    // ... 其他代码不变
    @GetMapping("/users")
    public List<User> getUsers() {
        return service.getUsers();
    }
}

// 方案二：添加@ResponseBody
@Controller
public class IndexController {
    // ... 其他代码不变
    @GetMapping("/users")
    @ResponseBody
    public List<User> getUsers() {
        return service.getUsers();
    }
}

修改后访问/users会直接返回JSON格式的用户列表，无需模板页面。

方向2：渲染Thymeleaf模板页面展示数据

如果需要在网页上展示用户数据，需完成以下两步：

1. 在src/main/resources/templates目录下创建users.html模板文件，示例如下：

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title>用户列表</title>
</head>
<body>
    <h1>用户列表</h1>
    <table>
        <tr>
            <th>ID</th>
            <th>姓名</th>
            <th>邮箱</th>
        </tr>
        <tr th:each="user : ${users}">
            <td th:text="${user.id}"></td>
            <td th:text="${user.fname + ' ' + user.lname}"></td>
            <td th:text="${user.email}"></td>
        </tr>
    </table>
</body>
</html>

2. 修改getUsers方法，将用户列表添加到Model中，并返回模板名称：

@GetMapping("/users")
public String getUsers(Model model) {
    List<User> users = service.getUsers();
    model.addAttribute("users", users);
    return "users";
}

修改后访问/users会渲染users.html页面并展示用户数据。

内容的提问来源于stack exchange，提问作者RDX