JDK之Enumeration

快来打我* 2022-03-21 10:49 149阅读 0赞

## 源码 ##

package java.util;
    
    /** * @author Lee Boynton * @since JDK1.0 */
    public interface Enumeration<E> { 
        boolean hasMoreElements();
        E nextElement();
    }

## Enumeration的遍历 ##

### Spring之ContextCleanupListener源码 ###

package org.springframework.web.context;
    
    import java.util.Enumeration;
    import javax.servlet.ServletContext;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    
    import org.springframework.beans.factory.DisposableBean;
    
    public class ContextCleanupListener implements ServletContextListener { 
    
    	private static final Log logger = LogFactory.getLog(ContextCleanupListener.class);
    
    
    	@Override
    	public void contextInitialized(ServletContextEvent event) { 
    	}
    
    	@Override
    	public void contextDestroyed(ServletContextEvent event) { 
    		cleanupAttributes(event.getServletContext());
    	}
    
    	static void cleanupAttributes(ServletContext sc) { 
    		Enumeration<String> attrNames = sc.getAttributeNames();
    		// 测试此枚举是否包含更多的元素
    		while (attrNames.hasMoreElements()) { 
    			// 如果此枚举对象至少还有一个可提供的元素，则返回此枚举的下一个元素。
    			String attrName = attrNames.nextElement();
    			if (attrName.startsWith("org.springframework.")) { 
    				Object attrValue = sc.getAttribute(attrName);
    				if (attrValue instanceof DisposableBean) { 
    					try { 
    						((DisposableBean) attrValue).destroy();
    					}
    					catch (Throwable ex) { 
    						logger.error("Couldn't invoke destroy method of attribute with name '" + attrName + "'", ex);
    					}
    				}
    			}
    		}
    	}
    
    }

### 相关源码 ###

*  org.apache.catalina.core.ApplicationContext.getAttributeNames()方法

@Override
    public Enumeration<String> getAttributeNames() { 
        Set<String> names = new HashSet<>();
        names.addAll(attributes.keySet());
        return Collections.enumeration(names);
    }

*  java.util.Collections.enumeration(Collection)方法

public static <T> Enumeration<T> enumeration(final Collection<T> c) { 
        return new Enumeration<T>() { 
            private final Iterator<T> i = c.iterator();
    
            public boolean hasMoreElements() { 
                return i.hasNext();
            }
    
            public T nextElement() { 
                return i.next();
            }
        };
    }