来看Buffer组。 Buffer BlockingBuffer BoundedFifoBuffer PriorityBuffer UnboundedFifoBuffer BufferUtils Buffer是定义在org.apache.commons.collections包下面的接口,用于表示按一定顺序除去成员对象的collection如队列等。具体的实现类在org.apache.commons.collections.buffer包下可以找到。 BufferUtils提供很多静态/工具方法装饰现有的Buffer实例,如将其装饰成BlockingBuffer、执行类型检查的TypedBuffer、或者不可改变的UnmodifiableBuffer等等。 最简单直接的Buffer实现类是UnboundedFifoBuffer,提供先进先出的大小可变的队列。而BoundedFifoBuffer则是对其大小进行了限制,是固定大小的先进先出队列。BlockingBuffer要在多线程的环境中才能体现出它的价值,尤其是当我们需要实现某种流水线时这个BlockingBuffer很有用:每个流水线上的组件从上游的BlockingBuffer获取数据,处理后放到下一个BlockingBuffer中依次传递。BlockingBuffer的核心特色通俗点说就是如果你向它要东西,而它暂时还没有的话,你可以一直等待直至拿到为止。PriorityBuffer则提供比一般的先进先出Buffer更强的控制力:我们可以自定义Comparator给它,告诉它怎么判定它的成员的先后顺序,优先级最高的最先走。 为了方便和清晰的需要,我在这里只举一个BoundedFifoBuffer,包装成TypedBuffer,看看在具体的代码中通常如何使用Buffer:(还是沿用上次的Book类) package sean.study.commons.collections; import java.util.Iterator; import org.apache.commons.collections.Buffer; import org.apache.commons.collections.BufferUtils; import org.apache.commons.collections.buffer.BoundedFifoBuffer; import org.apache.commons.lang.StringUtils; public class BufferUsage { public static void main(String[] args) { demoBufferUsage(); } public static void demoBufferUsage() { System.out.println(StringUtils.center(" demoBagUsage ", 40, "=")); // data setup Book book1 = new Book("Refactoring Workbook", "7-5083-2208-8", 29.8); Book book2 = new Book("J2EE Design Patterns", "7-5083-3099-4", 45); Book book3 = new Book("Agile Software Development", "7-5083-1503-0", 59); Book book4 = new Book("Professional JSP", "7-5053-8005-2", 100); // create a Buffer Buffer buffer = BufferUtils.typedBuffer(new BoundedFifoBuffer(3), Book.class); buffer.add(book1); buffer.add(book2); buffer.add(book3); Book removed = (Book) buffer.remove(); System.out.println("Removed:"); System.out.println(removed); buffer.add(book4); // get items in buffer for (int i = 0; i < 3; i++) { System.out.println(buffer.get()); buffer.remove(); } System.out.println(StringUtils.repeat("=", 40)); } } 以下是运行结果: ============= demoBagUsage ============= Removed: sean.study.commons.collections.Book@e09713[ name=Refactoring Workbook ISBN=7-5083-2208-8 retailPrice=29.8 ] Remaining: sean.study.commons.collections.Book@e09713[ name=J2EE Design Patterns ISBN=7-5083-3099-4 retailPrice=45.0 ] sean.study.commons.collections.Book@47b480[ name=Agile Software Development ISBN=7-5083-1503-0 retailPrice=59.0 ] sean.study.commons.collections.Book@19b49e6[ name=Professional JSP ISBN=7-5053-8005-2 retailPrice=100.0 ] ======================================== |
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来自: moonboat > 《Jakarta Commons》