java - WebApplicationInitializer container.addFilter() 返回 null

Question

我正在创建一个基于 REST 的 Web 应用程序，以 AngularJS 作为前端，以 REST 为基础的后端(使用 Spring 4 )。我遵循此处找到的基于代码的配置方法:WebApplicationInitializer

当我在服务器上运行该项目时，我在该行中得到一个空值:

FilterRegistration.Dynamic filter =  container.addFilter("prerender", seoFilter);

我错过了什么？我对使用注释从头开始创建网络应用程序有点陌生。

这是有问题的类:

public class MyWebAppInitializer implements WebApplicationInitializer {

@Override
public void onStartup(ServletContext container) throws ServletException {

XmlWebApplicationContext appContext = new XmlWebApplicationContext();
appContext.setConfigLocation("classpath:MyContext.xml");

ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(appContext));
dispatcher.setLoadOnStartup(1);
dispatcher.addMapping("/api/*");

com.github.greengerong.PreRenderSEOFilter seoFilter = new com.github.greengerong.PreRenderSEOFilter();
FilterRegistration.Dynamic filter =  container.addFilter("prerender", seoFilter);
filter.setInitParameter("prerenderToken", "123456789123456789");
filter.addMappingForUrlPatterns(null , true, "/*");

ServletRegistration.Dynamic initSysConfiguration
        = container.addServlet("initSysConfiguration", new InitSystemConfigurations());
initSysConfiguration.setLoadOnStartup(1);
initSysConfiguration.addMapping("/InitSystemConfigurations");

}

这一行给我空

com.github.greengerong.PreRenderSEOFilter seoFilter = new com.github.greengerong.PreRenderSEOFilter();

我尝试过，但结果相同

FilterRegistration.Dynamic filter1 =  container.addFilter("prerender",  com.github.greengerong.PreRenderSEOFilter.class);

Answer 1

当方法 addFilter 返回 null 时，意味着该名称已经存在 a filter registered。

Returns:
a FilterRegistration object that may be used to further configure the given filter, or null if this ServletContext already contains a complete FilterRegistration for a filter with the given filterName or if the same filter instance has already been registered with this or another ServletContext in the same container

确保您没有已注册此过滤器的 web.ml。

另一个技巧是不要自己实现WebApplicationInitializer，而是扩展AbstractDispatcherServletInitializer并实现所需的方法。

public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

    @Override
    public void onStartup(ServletContext container) throws ServletException {
        super.onStartup(container);

        com.github.greengerong.PreRenderSEOFilter seoFilter = new com.github.greengerong.PreRenderSEOFilter();
        FilterRegistration.Dynamic filter =  container.addFilter("prerender", seoFilter);
        filter.setInitParameter("prerenderToken", "123456789123456789");
        filter.addMappingForUrlPatterns(null , true, "/*");

        ServletRegistration.Dynamic initSysConfiguration
                = container.addServlet("initSysConfiguration", new InitSystemConfigurations());
        initSysConfiguration.setLoadOnStartup(1);
        initSysConfiguration.addMapping("/InitSystemConfigurations");

    }

    protected WebApplicationContext createServletApplicationContext() {
        XmlWebApplicationContext appContext = new XmlWebApplicationContext();
        appContext.setConfigLocation("classpath:MyContext.xml");
        return appContext;
    }

    protected String[] getServletMappings() {
        return new String[] {"/api/*"};
    }

}