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要隨時切換一組端點，我們可以使用 Filter。 通過使用 endpoint.regex 模式匹配請求的端點，我們可以允許成功匹配或返回 503 HTTP 響應狀態碼，用於不成功的匹配。

因此，讓我們通過擴展 OncePerRequestFilter 來 定義 DynamicEndpointFilter 類：

public class DynamicEndpointFilter extends OncePerRequestFilter {
    private Environment environment;

    // ...
}

進一步，我們需要通過覆蓋 doFilterInternal()方法來添加模式匹配的邏輯：

@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, 
  FilterChain filterChain) throws ServletException, IOException {
    String path = request.getRequestURI();
    String regex = this.environment.getProperty("endpoint.regex");
    Pattern pattern = Pattern.compile(regex);
    Matcher matcher = pattern.matcher(path);
    boolean matches = matcher.matches();

    if (!matches) {
        response.sendError(HttpStatus.SERVICE_UNAVAILABLE.value(), "Service is unavailable");
    } else {
        filterChain.doFilter(request,response);
    }
}

我們必須注意到 <em>endpoint.regex</em> 屬性的初始值為“.*”，這允許所有請求通過此 Filter。

3. 使用環境屬性切換

本節將學習如何通過從 extra.properties 文件中獲取環境屬性來執行熱重載。

3.1. 重新加載配置

為此，我們首先定義一個使用 FileChangedReloadingStrategy 的 Bean，用於 PropertiesConfiguration：

@Bean
@ConditionalOnProperty(name = "dynamic.endpoint.config.location", matchIfMissing = false)
public PropertiesConfiguration propertiesConfiguration(
  @Value("${dynamic.endpoint.config.location}") String path,
  @Value("${spring.properties.refreshDelay}") long refreshDelay) throws Exception {
    String filePath = path.substring("file:".length());
    PropertiesConfiguration configuration = new PropertiesConfiguration(
      new File(filePath).getCanonicalPath());
    FileChangedReloadingStrategy fileChangedReloadingStrategy = new FileChangedReloadingStrategy();
    fileChangedReloadingStrategy.setRefreshDelay(refreshDelay);
    configuration.setReloadingStrategy(fileChangedReloadingStrategy);
    return configuration;
}

需要注意的是，這些屬性的來源是通過 dynamic.endpoint.config.location 屬性在 application.properties 文件中確定的。此外，重新加載發生在 1 秒的延遲後，這是由 spring.properties.refreshDelay 屬性定義的。

接下來，我們需要在運行時讀取特定於端點的屬性。因此，讓我們定義 EnvironmentConfigBean，並使用屬性獲取器：

@Component
public class EnvironmentConfigBean {

    private final Environment environment;

    public EnvironmentConfigBean(@Autowired Environment environment) {
        this.environment = environment;
    }

    public String getEndpointRegex() {
        return environment.getProperty("endpoint.regex");
    }

    public boolean isFooEndpointEnabled() {
        return Boolean.parseBoolean(environment.getProperty("endpoint.foo"));
    }

    public Environment getEnvironment() {
        return environment;
    }
}

接下來，讓我們創建一個 FilterRegistrationBean 來註冊 DynamicEndpointFilter：

@Bean
@ConditionalOnBean(EnvironmentConfigBean.class)
public FilterRegistrationBean<DynamicEndpointFilter> dynamicEndpointFilterFilterRegistrationBean(
  EnvironmentConfigBean environmentConfigBean) {
    FilterRegistrationBean<DynamicEndpointFilter> registrationBean = new FilterRegistrationBean<>();
    registrationBean.setFilter(new DynamicEndpointFilter(environmentConfigBean.getEnvironment()));
    registrationBean.addUrlPatterns("*");
    return registrationBean;
}

3.2. 驗證

首先，讓我們運行應用程序並訪問 bar1</em/> 或 bar2</em/> API：

$ curl -iXGET http://localhost:9090/bar1
HTTP/1.1 200 
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 4
Date: Sat, 12 Nov 2022 12:46:32 GMT

bar1

endpoint.regex=.*/foo

$ curl -iXGET http://localhost:9090/bar1
HTTP/1.1 503 
Content-Type: application/json
Transfer-Encoding: chunked
Date: Sat, 12 Nov 2022 12:56:12 GMT
Connection: close

{"timestamp":1668257772354,"status":503,"error":"Service Unavailable","message":"Service is unavailable","path":"/springbootapp/bar1"}

$ curl -iXGET http://localhost:9090/foo
HTTP/1.1 200 
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 3
Date: Sat, 12 Nov 2022 12:57:39 GMT

foo

@Component
@RefreshScope
public class EndpointRefreshConfigBean {

    private boolean foo;
    private String regex;

    public EndpointRefreshConfigBean(@Value("${endpoint.foo}") boolean foo, 
      @Value("${endpoint.regex}") String regex) {
        this.foo = foo;
        this.regex = regex;
    }
    // getters and setters
}

@GetMapping("/foo")
public ResponseEntity<String> fooHandler() {
    if (endpointRefreshConfigBean.isFoo()) {
        return ResponseEntity.status(200).body("foo");
    } else {
        return ResponseEntity.status(503).body("endpoint is unavailable");
    }
}

$ curl -isXGET http://localhost:9090/foo
HTTP/1.1 200
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 3
Date: Sat, 12 Nov 2022 15:28:52 GMT

foo

endpoint.foo=false

$ curl -Is --request POST 'http://localhost:8081/actuator/refresh'
HTTP/1.1 200
Content-Type: application/vnd.spring-boot.actuator.v3+json
Transfer-Encoding: chunked
Date: Sat, 12 Nov 2022 15:34:24 GMT

$ curl -isXGET http://localhost:9090/springbootapp/foo
HTTP/1.1 503
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 23
Date: Sat, 12 Nov 2022 15:35:26 GMT
Connection: close

endpoint is unavailable