java - Spring - 如何在局部 View 中访问对象

Question

我正在使用 Spring Boot 和 Fremarker 作为模板引擎创建一个简单的博客应用程序。所以基本上我有作者和帖子。我有一个 navbar.tfl，它是局部 View 。因此，当我在此部分 View 中选择“作者”下拉列表时，我想列出所有作者的姓名，并包含一个链接以显示他们的所有帖子。

<nav class="navbar navbar-default">
  <div class="container-fluid">
    <div class="navbar-header">
      <a class="navbar-brand" href="/">FSM IT</a>
    </div>
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
      <ul class="nav navbar-nav">
        <li><a href="/">Home</a></li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Posts <span class="caret"></span></a>
          <ul class="dropdown-menu">
            <li><a href="/post/list">List</a></li>
          </ul>
        </li>
        <li class="dropdown">
          <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Authors <span class="caret"></span></a>
          <ul class="dropdown-menu">

            <!-- GET ALL AUTHORS HERE. HOW? -->

          </ul>
        </li>
      </ul>
      <p class="navbar-text navbar-right">Signed in as <a href="#" class="navbar-link">Guest User</a></p>
    </div>
  </div>
</nav>

问题是导航栏是一个局部 View ，所以它被所有 View 共享。我知道我们可以在 Controller 中执行类似 model.addAttribute("authors", authorRepository.findAll()) 之类的操作以将其传递给 View ，但由于导航栏是部分的，因此我必须在所有 Controller 中执行此操作。

在我看来，在 Ruby on Rails 中我会做这样的事情:

<% Author.all.each do |author| %>

然后在我的导航栏部分 View 中读取所有作者的姓名。

但是对于 Spring，我不知道该怎么做。

你能帮我吗？

这是我的作者库(它扩展了 CrudRepository，所以我有一个作者的 findAll 方法):

package com.example.repository;

import com.example.domain.Author;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface AuthorRepository extends CrudRepository<Author, Long> {

}

作者域:

package com.example.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import java.util.List;

@Entity
public class Author {

  @Id
  @GeneratedValue
  private Long id;
  private String firstName;
  private String lastName;
  private String email;

  // Posts
  @OneToMany(mappedBy = "author")
  private List<Post> posts;

  private Author() {}

  public Author(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }

  public Long getId() {
    return id;
  }

  public void setId(Long id) {
    this.id = id;
  }

  public String getFirstName() {
    return firstName;
  }

  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }

  public String getLastName() {
    return lastName;
  }

  public void setLastName(String lastName) {
    this.lastName = lastName;
  }

  public String getEmail() {
    return email;
  }

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

  @Override
  public String toString() {
    return "Author{" +
            "id=" + id +
            ", firstName='" + firstName + '\'' +
            ", lastName='" + lastName + '\'' +
            '}';
  }
}

Answer 1

您可以使用 @ModelAttribute Controller 中的注释:

@ModelAttribute methods are used to populate the model with commonly needed attributes for example to fill a drop-down with states or with pet types, or to retrieve a command object like Account in order to use it to represent the data on an HTML form.

@ModelAttribute("authors")
public Iterable<Author> getAuthors(){
    return authorRepository.findAll();
}

这会将 authors 模型属性添加到您的 Spring MVC 模型中。如果您将它放在您的 Controller 中，您将在您的模板中自动使用此属性。

如果您需要在许多 Controller 上使用此模型属性，请查看此处所述的 @ControllerAdvice 注释:

@ModelAttribute methods can also be defined in an @ControllerAdvice-annotated class and such methods apply to many controllers. See the the section called “Advising controllers with @ControllerAdvice and @RestControllerAdvice” section for more details.