责任链设计模式

责任链的应用场景

• Servlet API 中的 Filter 过滤器
• MVC 框架中的拦截器
• . . .

简单使用责任链模式拆分 Servlet API 中的过滤器

模拟 Servlet 中的 Request 对象

/**
 * @desc <b>模拟 Servlet 中的 Request 对象</b>
 * 
 * @author jiang ru yi
 */
public class HttpServletRequest {

    private String requestContext;
    private Map<String, Object> requestParam = new HashMap<>();

    public String getRequestContext() {
        return requestContext;
    }

    public void setRequestContext(String requestContext) {
        this.requestContext = requestContext;
    }

    public void setRequestParam(Map<String, Object> requestParam) {
        this.requestParam = requestParam;
    }
    
    public Object setAttribute(String key, Object value) {
        return requestParam.put(key, value);
    }
    
    public Object getAttribute(String key) {
        return requestParam.get(key);
    }
    
    public Object removeAttribute(String key) {
        return requestParam.remove(key);
    }
    
}

模拟 Servlet 中的 Response 对象

/**
 * @desc <b>模拟 Servlet 中的 Response 对象</b>
 * 
 * @author jiang ru yi
 */
public class HttpServletResponse {

    private String responseContext;

    public String getResponseContext() {
        return responseContext;
    }

    public void setResponseContext(String responseContext) {
        this.responseContext = responseContext;
    }

}

过滤器抽象层

/**
 * @desc <b>公用的过滤器抽象层</b>
 * 
 * @author jiang ru yi
 */
public abstract class HttpFilter {
    
    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain);

}

过滤器调度

/**
 * @desc <b>过滤器的调度器</b>
 * 
 * @author jiang ru yi
 */
public class FilterChain {

    private List<HttpFilter> filters = new ArrayList<>();
    private int currFilter;

    public boolean addFilter(HttpFilter filter) {
        return filters.add(filter);
    }
    
    public boolean removeFilter(HttpFilter filter) {
        return filters.remove(filter);
    }
    
    public void doFilter(HttpServletRequest request, HttpServletResponse response) {
        if (currFilter++ == filters.size()) return;
        
        filters.get(currFilter - 1).doFilter(request, response, this);
    }

}

Junit 测试

public static void main(String[] args) {
    HttpServletRequest request = new HttpServletRequest();
    request.setRequestContext("<EvE>, Y(OvO)Y");
    request.setAttribute("user", "administrator");

    HttpServletResponse response = new HttpServletResponse();

    FilterChain chain = new FilterChain();
    chain.addFilter(new CharacterSetFilter());
    chain.addFilter(new PowerFilter());

    chain.doFilter(request, response);

    System.out.println(request.getRequestContext());
}

抽象层子类 : 字符过滤器

/**
 * @desc <b>过滤请求中的危险符号( < > )</b>
 * 
 * @author jiang ru yi
 */
public class CharacterSetFilter extends HttpFilter {

    @Override
    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {
        String context = request.getRequestContext();
        String result = context.replaceAll("<", "&le;").replaceAll(">", "&lt;");
        request.setRequestContext(result);
        chain.doFilter(request, response);
    }

}

抽象层子类 : 校验用户是否登录

/**
 * @desc <b>过滤用户是否登录</b>
 * 
 * @author jiang ru yi
 */
public class PowerFilter extends HttpFilter {

    @Override
    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {
        Object attribute = request.getAttribute("user");
        if (null != attribute) {
            chain.doFilter(request, response);
        } else {
            throw new RuntimeException("user not login");
        }
    }

}