如何在不修改 Web 的情况下向 Servlet 添加过滤器.xml

只需执行与容器相同的工作即可。即，重新发明责任链设计模式的轮子，就像servlet过滤器使用的盖子一样。

public class GodFilter implements Filter {

    private Map<Pattern, Filter> filters = new LinkedHashMap<Pattern, Filter>();

    @Override
    public void init(FilterConfig config) throws ServletException {
        Filter1 filter1 = new Filter1();
        filter1.init(config);
        filters.put(new Pattern("/foo/*"), filter1);

        Filter2 filter2 = new Filter2();
        filter2.init(config);
        filters.put(new Pattern("*.bar"), filter2);

        // ...
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
        HttpServletRequest hsr = (HttpServletRequest) request;
        String path = hsr.getRequestURI().substring(hsr.getContextPath().length());
        GodFilterChain godChain = new GodFilterChain(chain);

        for (Entry<Pattern, Filter> entry : filters.entrySet()) {
            if (entry.getKey().matches(path)) {
                godChain.addFilter(entry.getValue());
            }
        }

        godChain.doFilter(request, response);
    }

    @Override
    public void destroy() {
        for (Filter filter : filters.values()) {
            filter.destroy();
        }
    }

}

使用那些小的帮助器类（如有必要，可以将其设置为上述的嵌套类）：private staticGodFilter

public class Pattern {

    private int position;
    private String url;

    public Pattern(String url) {
        this.position = url.startsWith("*") ? 1
                      : url.endsWith("*") ? -1
                      : 0;
        this.url = url.replaceAll("/?\\*", "");
    }

    public boolean matches(String path) {
        return (position == -1) ? path.startsWith(url)
             : (position == 1) ? path.endsWith(url)
             : path.equals(url);
    }

}

和

public class GodFilterChain implements FilterChain {

    private FilterChain chain;
    private List<Filter> filters = new ArrayList<Filter>();
    private Iterator<Filter> iterator;

    public GodFilterChain(FilterChain chain) {
        this.chain = chain;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
        if (iterator == null) {
            iterator = filters.iterator();
        }

        if (iterator.hasNext()) {
            iterator.next().doFilter(request, response, this);
        } else {
            chain.doFilter(request, response);
        }
    }

    public void addFilter(Filter filter) {
        if (iterator != null) {
            throw new IllegalStateException();
        }

        filters.add(filter);
    }

}

如有必要，您还可以向 XML 配置文件提供所有可能的筛选器，以便最终获得更简单的配置。您可以使用反射在 中创建滤镜。init()GodFilter

哦，别介意，这就是容器已经在做的事情...web.xml

Servlet 3.0 具有定义过滤器的注释。不再需要在web.xml中声明它。@WebFilter

但不支持从筛选器加载筛选器。你可以自己实现它：它“只是”责任链模式，但你为什么要这样做呢？