# 9.2.4　配置自定义的用户服务

假设我们需要认证的用户存储在非关系型数据库中，如 Mongo 或 Neo4j，在这种情况下，我们需要提供一个自定义的 UserDetailsService 接口实现。 UserDetailsService 接口非常简单：

```java
public interface UserDetailsService {
  UserDetails loadUserByUsername(String username) throws UsernameNotFoundException;
}
```

我们所需要做的就是实现 loadUserByUsername() 方法，根据给定的用户名来查找用户。loadUserByUsername() 方法会返回代表给定用户的 UserDetails 对象。如下的程序清单展现了一个 UserDetailsService 的实现，它会从给定的 SpitterRepository 实现中查找用户。

{% code title="程序清单 9.4　从 SpitterRepository 中查找 UserDetails 对象" %}

```java
package spittr.security;

import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.SimpleGrantAuthority;
import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;

import spittr.Spitter;
import spittr.data.SpitterRepository;

public class SpitterUserService(SpitterRepository spitterRepository) {
  
  private final SpitterRepository spitterRepository;
  
  public SpitterUserService(SpitterRepository spitterRepository){
    this.spitterRepository = spitterRepository;
  }
  
  @Override
  public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
    Spitter spitter = spitterRepository.findByUsername(username);
    if (spitter != null) {
      List<GrantedAuthority> authorities = new ArrayList<>();
      authorities.add(new SimpleGrantedAuthority("ROLE_SPITTER"));
    }
    
    return new User(
      spitter.getUsername(),
      spitter.getPassword(),
      authorities);
  }
  throw new UsernameNotFoundException(
    "User '" + username + "' not found.");
}
```

{% endcode %}

SpitterUserService 有意思的地方在于它并不知道用户数据存储在什么地方。设置进来的 SpitterRepository 能够从关系型数据库、文档数据库或图数据中查找 Spitter 对象，甚至可以伪造一个。SpitterUserService 不知道也不会关心底层所使用的数据存储。它只是获得 Spitter 对象，并使用它来创建 User 对象。（User 是 UserDetails 的具体实现。）

为了使用 SpitterUserService 来认证用户，我们可以通过 userDetailsService() 方法将其设置到安全配置中：

```java
@Autowired
SpitterRepository spitterRepository;

@Override
protected void configure(AuthenticationManagerBuilder auth) throws Exception {
  auth
    .userDetailsService(new SpitterUserService(spitterRepository));
}
```

userDetailsService() 方法（类似于 jdbcAuthentication()、ldapAuthentication() 以及 inMemoryAuthentication()）会配置一个用户存储。不过，这里所使用的不是 Spring 所提供的用户存储，而是使用 UserDetailsService 的实现。

另外一种值得考虑的方案就是修改 Spitter，让其实现 UserDetails。这样的话，loadUserByUsername() 就能直接返回 Spitter 对象了，而不必再将它的值复制到 User 对象中。


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://potoyang.gitbook.io/spring-in-action-v4/untitled-3/untitled-4/untitled.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.