浅述 Spring / SpringMVC 框架中用到的哪些设计模式（下）

// 定义一个事件,继承自ApplicationEvent并且写相应的构造函数
public class DemoEvent extends ApplicationEvent {
    private static final long serialVersionUID = 1L;
    private String message;
    public DemoEvent(Object source,String message){
        super(source);
        this.message = message;
    }
    public String getMessage() {
         return message;
    }
}
// 定义一个事件监听者,实现ApplicationListener接口，重写 onApplicationEvent() 方法；
@Component
public class DemoListener implements ApplicationListener<DemoEvent>{
    //使用onApplicationEvent接收消息
    @Override
    public void onApplicationEvent(DemoEvent event) {
        String msg = event.getMessage();
        System.out.println("接收到的信息是："+msg);
    }
}
// 发布事件，可以通过ApplicationEventPublisher  的 publishEvent() 方法发布消息。
@Component
public class DemoPublisher {
    @Autowired
    ApplicationContext applicationContext;
    public void publish(String message){
        //发布事件
        applicationContext.publishEvent(new DemoEvent(this, message));
    }
}
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# 对象适配器
public class MethodBeforeAdviceInterceptor implements MethodInterceptor, BeforeAdvice, Serializable {
    private final MethodBeforeAdvice advice;
    public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
        Assert.notNull(advice, "Advice must not be null");
        this.advice = advice;
    }
    public Object invoke(MethodInvocation mi) throws Throwable {
        this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
        return mi.proceed();
    }
}
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# 对象适配器
public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {
    private final AfterReturningAdvice advice;
    public AfterReturningAdviceInterceptor(AfterReturningAdvice advice) {
        Assert.notNull(advice, "Advice must not be null");
        this.advice = advice;
    }
    public Object invoke(MethodInvocation mi) throws Throwable {
        Object retVal = mi.proceed();
        this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
        return retVal;
    }
}
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public interface FilterChain {
    /**
     * Causes the next filter in the chain to be invoked, or if the calling
     * filter is the last filter in the chain, causes the resource at the end of
     * the chain to be invoked.
     *
     * @param request
     *            the request to pass along the chain.
     * @param response
     *            the response to pass along the chain.
     */
    public void doFilter(ServletRequest request, ServletResponse response)
            throws IOException, ServletException;
}
/**
 * Implementation of <code>javax.servlet.FilterChain</code> used to manage
 * the execution of a set of filters for a particular request.  When the
 * set of defined filters has all been executed, the next call to
 * <code>doFilter()</code> will execute the servlet's <code>service()</code>
 * method itself.
 */
public final class ApplicationFilterChain implements FilterChain {
    private ApplicationFilterConfig[] filters = new ApplicationFilterConfig[0];
    @Override
    public void doFilter(ServletRequest request, ServletResponse response)
        throws IOException, ServletException {
        if( Globals.IS_SECURITY_ENABLED ) {
            final ServletRequest req = request;
            final ServletResponse res = response;
            try {
                java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedExceptionAction<Void>() {
                        @Override
                        public Void run()
                            throws ServletException, IOException {
                            internalDoFilter(req,res);
                            return null;
                        }
                    }
                );
            } catch( PrivilegedActionException pe) {
                ...
            }
        } else {
            internalDoFilter(request,response);
        }
    }
    private void internalDoFilter(ServletRequest request,
                                  ServletResponse response)
        throws IOException, ServletException {
        // Call the next filter if there is one
        if (pos < n) {
            ApplicationFilterConfig filterConfig = filters[pos++];
            Filter filter = filterConfig.getFilter();
            if (request.isAsyncSupported() && "false".equalsIgnoreCase(
                    filterConfig.getFilterDef().getAsyncSupported())) {
                request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
            }
            if( Globals.IS_SECURITY_ENABLED ) {
                final ServletRequest req = request;
                final ServletResponse res = response;
                Principal principal =
                    ((HttpServletRequest) req).getUserPrincipal();
                Object[] args = new Object[]{req, res, this};
                SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
            } else {
                filter.doFilter(request, response, this);
            }
            return;
        }
        ...
    }
    /**
     * Add a filter to the set of filters that will be executed in this chain.
     *
     * @param filterConfig The FilterConfig for the servlet to be executed
     */
    void addFilter(ApplicationFilterConfig filterConfig) {
        // Prevent the same filter being added multiple times
        for(ApplicationFilterConfig filter:filters)
            if(filter==filterConfig)
                return;
        if (n == filters.length) {
            ApplicationFilterConfig[] newFilters =
                new ApplicationFilterConfig[n + INCREMENT];
            System.arraycopy(filters, 0, newFilters, 0, n);
            filters = newFilters;
        }
        filters[n++] = filterConfig;
    }
}
public interface Filter {
    /**
     *
     * @param filterConfig The configuration information associated with the
     *                     filter instance being initialised
     *
     * @throws ServletException if the initialisation fails
     */
    public default void init(FilterConfig filterConfig) throws ServletException {}
    /**
     *
     * @param request  The request to process
     * @param response The response associated with the request
     * @param chain    Provides access to the next filter in the chain for this
     *                 filter to pass the request and response to for further
     *                 processing
     *
     */
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException;
    public default void destroy() {}
}
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