问题

我有一个User类，两个JSP页面和一个控制器。我想要注册一个用户，将他们的详细信息存储在数据库（H2）中，并在注册后显示用户的名字。

这是我的```home.jsp```页面 -

```jsp
<form action="addUser">
    <label>Name: </label><input type="text" name="name"/>
    <label>Id: </label><input type="number" name="id"/>
    <input type="submit" />
</form>

这是我的控制器 -

package com.example.demo;

import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class HomeController {

    @Autowired
    UserRepo usrrepoobj;
    
    @RequestMapping("/")
    public String home() {
        return "home.jsp";
    }
    
    @RequestMapping("addUser")
    public ModelAndView addUser(@RequestParam int id, User usr) {
        usrrepoobj.save(usr);
        User obj = usrrepoobj.findById(id).orElse(null);
        ModelAndView mv = new ModelAndView();
        mv.addObject(obj);
        mv.setViewName("afterRegister.jsp");
        
        //甚至这个也不起作用
//        usrrepoobj.save(usr);
//        User obj = usr;
//        ModelAndView mv = new ModelAndView();
//        mv.addObject(obj);
//        mv.setViewName("afterRegister.jsp");
        //甚至这个也不起作用
        
        return mv;
    }
    
}

这是我的afterRegister.jsp页面 -

Registered as ${obj.name}

对象已添加到数据库。在显示数据时我做错了什么？

<details>
<summary>英文:</summary>

I have a User class, two JSP and one controller. I want to register a user, store their details in a database (H2) and display user&#39;s name after registration.

This is my ```home.jsp``` - 

<form action="addUser">
<label>Name: </label><input type="text" name="name"/>
<label>Id: </label><input type="number" name="id"/>
<input type="submit" />
</form>

This is my controller - 

package com.example.demo;

import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class HomeController {

@Autowired
UserRepo usrrepoobj;

@RequestMapping("/")
public String home()
{
	return "home.jsp";
}

@RequestMapping("addUser")
public ModelAndView addUser(@RequestParam int id, User usr)
{
	usrrepoobj.save(usr);
	User obj = usrrepoobj.findById(id).orElse(null);
	ModelAndView mv = new ModelAndView();
	mv.addObject(obj);
	mv.setViewName("afterRegister.jsp");
	
	//EVEN THIS DOESNT WORK

// usrrepoobj.save(usr);
// User obj = usr;
// ModelAndView mv = new ModelAndView();
// mv.addObject(obj);
// mv.setViewName("afterRegister.jsp");
//EVEN THIS DOESNT WORK

	return mv;
}

}

This is my ```afterRegister.jsp``` - 

Registered as ${obj.name}

The object gets added to the database. What am I doing wrong when it comes to displaying the data in the next JSP?

</details>


# 答案1
**得分**: 1

很可能你不知道已添加用户的ID，这就是为什么你的`findById`始终返回`null`的原因。只需从`save()`方法中返回用户即可。展示一下你的用户实体。

```java
@RequestMapping("addUser")
public String addUser(@RequestParam int id, User usr, Model model)
{
    User obj = usrrepoobj.save(usr);
    model.addAttribute("obj", obj);
    
    return "afterRegister.jsp";
}

请注意，代码部分没有被翻译。

@RequestMapping("addUser")
public String addUser(@RequestParam int id, User usr, Model model)
{
    User obj = usrrepoobj.save(usr);
    model.addAttribute("obj", obj);
    
    return "afterRegister.jsp";
}

答案2

得分: 0

在控制器中进行以下更改：

usrrepoobj.save(usr);
User obj = usrrepoobj.findById(id).orElse(null);
ModelAndView mv = new ModelAndView();
mv.addObject("object", obj); // 将此处更改
mv.setViewName("afterRegister.jsp");

在 afterRegister.jsp 文件中：

已注册为 ${object.name}

usrrepoobj.save(usr);
        User obj = usrrepoobj.findById(id).orElse(null);
        ModelAndView mv = new ModelAndView();
        mv.addObject("object",obj); //change this
        mv.setViewName("afterRegister.jsp");

Registered as ${object.name}