Referencing Environment Variables in web.xml

Question

I\'m pre-packaging a JSP web-app that relies on some file path settings found within web.xml. These settings are unknown at packaging time, because they reference a path the

Answer 1

If you're using Spring - you could pipe FilterConfig through ConfigurableBeanFactory.resolveEmbeddedValue to enable property placeholders interpolation support in web.xml.

Proxy class for make FilterConfig parameters resolvable.

public class ResolvableFilterConfig implements FilterConfig {

    private final FilterConfig source;
    private final ConfigurableBeanFactory resolver;

    public ResolvableFilterConfig(FilterConfig source, ConfigurableBeanFactory resolver) {
        this.source = source;
        this.resolver = resolver;
    }

    @Override
    public String getFilterName() {
        return source.getFilterName();
    }

    @Override
    public ServletContext getServletContext() {
        return source.getServletContext();
    }

    @Override
    public String getInitParameter(String name) {
        final String value = source.getInitParameter(name);
        return resolver.resolveEmbeddedValue(value);
    }

    @Override
    public Enumeration getInitParameterNames() {
        return source.getInitParameterNames();
    }
}

Filter implementation sample code

    @Override
    public void init(FilterConfig config) throws ServletException {
        // configure
        final ServletContext servletContext = config.getServletContext();
        final AbstractApplicationContext aac = (AbstractApplicationContext) getRequiredWebApplicationContext(servletContext);
        final ConfigurableBeanFactory beanFactory = aac.getBeanFactory();
        config = new ResolvableFilterConfig(config, beanFactory);
        // ... do the rest
    }