Java web 过滤器使用@Value属性为null

问题：Java web 过滤器使用@Value属性为null

现象：

application.yaml配置文件如下：

app.system.id=20191010
app.service.secretkey=123456
过滤器配置

@WebFilter(urlPatterns = "/api/*", filterName = "SSOConfig")
public class SSOConfig implements Filter {

	 @Value("${app.system.id}")
 	 private String systemId;
	 @Value("${app.service.secretkey}")
 	 private String secretKey;
     @Override
     public void init(FilterConfig filterConfig) throws ServletException {

     }
	 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
		//本地开发阶段是可以获取到值得
		System.out.println(systemId);
		System.out.println(secretKey);
        filterChain.doFilter(request, response); 
     }
     @Override
     public void destroy() {

     }
}

分析：Javaweb项目启动时，加载顺序导致的。

在web.xml中各个元素的执行顺序：

context-param–>listener–>filter–>servlet

而拦截器是在Spring MVC中配置的，如果从整个项目中看，一个servlet请求的执行过程就变成了这样：

context-param–>listener–>filter–>servlet–>interceptor(指的是拦截器)->spring

因此注入的值为null，使用@Autowired注入bean的话，也是注入不了，值也为null。

思路：

将要注入的数据从filter分离，当服务启动完毕后,过滤方法中再调用。

解决：

可以使用static变量，然后再为变量赋值的方法实现。

@Component
public class SSOUtil {

    public static String systemId;
    public static String secretKey;

    @Value("${app.system.id}")
    public void setSystemId(String systemId) {
        SSOUtil.systemId=systemId;
    }

    @Value("${app.service.secretkey}")
    public void setSecretKey(String secretKey) {
        SSOUtil.secretKey=secretKey;
    }
    public static String getApp() {
        return systemId+":"+secretKey;
    }
}

@WebFilter(urlPatterns = "/api/*", filterName = "SSOConfig")
public class SSOConfig implements Filter {
     @Override
     public void init(FilterConfig filterConfig) throws ServletException {

     }
	 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
		System.out.println(SSOUtil.getApp());
        filterChain.doFilter(request, response); 
     }
     @Override
     public void destroy() {

     }
}