什麼是攔截過濾器模式?
攔截過濾器模式(Intercepting Filter Pattern)用于對應用程式的請求或響應做一些預處理/後處理。定義過濾器,并在把請求傳給實際目标應用程式之前應用在請求上。過濾器可以做認證/授權/記錄日志,或者跟蹤請求,然後把請求傳給相應的處理程式。以下是這種設計模式的實體。
過濾器(Filter) - 過濾器在請求處理程式執行請求之前或之後,執行某些任務。
過濾器鍊(Filter Chain) - 過濾器鍊帶有多個過濾器,并在 Target 上按照定義的順序執行這些過濾器。
Target - Target 對象是請求處理程式。
過濾管理器(Filter Manager) - 過濾管理器管理過濾器和過濾器鍊。
用戶端(Client) - Client 是向 Target 對象發送請求的對象。
如何實作?
public interface Filter {
public void execute(String request);
}
public class DebugFilter implements Filter {
public void execute(String request){
System.out.println("request log: " + request);
}
}
public class AuthenticationFilter implements Filter {
public void execute(String request){
System.out.println("Authenticating request: " + request);
}
}
public class FilterChain {
private List<Filter> filters = new ArrayList<Filter>();
private Target target;
public void addFilter(Filter filter){
filters.add(filter);
}
public void execute(String request){
for (Filter filter : filters) {
filter.execute(request);
}
target.execute(request);
}
public void setTarget(Target target){
this.target = target;
}
}
public class FilterManager {
FilterChain filterChain;
public FilterManager(Target target){
filterChain = new FilterChain();
filterChain.setTarget(target);
}
public void setFilter(Filter filter){
filterChain.addFilter(filter);
}
public void filterRequest(String request){
filterChain.execute(request);
}
}
public class Target {
public void execute(String request){
System.out.println("Executing request: " + request);
}
}
public class Client {
FilterManager filterManager;
public void setFilterManager(FilterManager filterManager){
this.filterManager = filterManager;
}
public void sendRequest(String request){
filterManager.filterRequest(request);
}
}
public class InterceptingFilterDemo {
public static void main(String[] args) {
FilterManager filterManager = new FilterManager(new Target());
filterManager.setFilter(new AuthenticationFilter());
filterManager.setFilter(new DebugFilter());
Client client = new Client();
client.setFilterManager(filterManager);
client.sendRequest("HOME");
}
}