java 新手练习小项目

package com.chen.nio; import lombok.extern.slf4j.Slf4j; import org.junit.jupiter.api.Test; import java.nio.IntBuffer; import java.util.stream.IntStream; /** * Buffer 测试：Buffer类中比较重要的几个属性如下 * <ul> * <li>position-游标，读和写默认都是从0开始，最大值为 limit-1</li> * <li>limit-最大上限，写模式下默认是 capacity 的值，读模式下为缓冲区的数据量大小</li> * <li>capacity-容量，并不是字节数的大小，指的是写入的数据对象的数量</li> * </ul> * * @author chenzihan * @date 2022/02/23 */ @Slf4j public class BufferTest { /** * 创建 Buffer 必须使用静态方法 allocate，创建完成后默认是写状态，具体的 api 可以参见具体的 Buffer 子类 */ @Test public void allocate() { IntBuffer intBuffer = IntBuffer.allocate(10); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * 在 buffer 中放数据 */ @Test public void put() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * 翻转：从写模式转换为读模式。 */ @Test public void flip() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); intBuffer.flip(); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * 从缓冲区中读取数据，默认从 index 为 0 开始读取，可以自己指定 index 进行读取 */ @Test public void get() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); intBuffer.flip(); IntStream.rangeClosed(1, 2) .forEach(i -> { // 指定 index 读取不会改变 position 的值 int result = intBuffer.get(i); log.info("result = {}", result); log.info("position = {}", intBuffer.position()); }); IntStream.rangeClosed(1, 4) .forEach(i -> { // 不指定 index 的值，会改变 position 的值 int result = intBuffer.get(); log.info("result = {}", result); log.info("position = {}", intBuffer.position()); }); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * 倒带：读取完以后，调用 rewind 方法可以重置 position 和 mark 的状态，从头开始读取 */ @Test public void rewind() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); intBuffer.flip(); IntStream.rangeClosed(1, 2) .forEach(i -> intBuffer.get()); intBuffer.rewind(); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * mark & reset，这两个方法一般配套使用，mark 记录 position 某一刻的状态，后续改变后，可以调用 reset 方法还原到 mark 时的状态 */ @Test public void reset() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); intBuffer.flip(); IntStream.rangeClosed(0, 4) .forEach(i -> { if (i == 2) { intBuffer.mark(); } int result = intBuffer.get(); log.info("result = {}", result); }); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); intBuffer.reset(); log.info("position = {}", intBuffer.position()); log.info("limit = {}", intBuffer.limit()); log.info("capacity = {}", intBuffer.capacity()); } /** * 清空缓冲区：会将 buffer 重置到初始的写状态，即 position = 0;limit = capacity;mark = -1; * 但是 clear 不会清空 buffer 的数组，所以通过 get(index) 还是可以获取固定位置下的元素 */ @Test public void clear() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(1, 5) .forEach(intBuffer::put); intBuffer.flip(); intBuffer.clear(); intBuffer.compact(); IntStream.rangeClosed(0, 4) .forEach(i -> { int result = intBuffer.get(i); log.info("result = {}", result); }); } /** * 压缩 buffer，具体规则参见 IntBuffer.compact 的注释 */ @Test public void compact() { IntBuffer intBuffer = IntBuffer.allocate(10); IntStream.rangeClosed(0, 4) .forEach(intBuffer::put); intBuffer.flip(); intBuffer.compact(); IntStream.rangeClosed(0, 9) .forEach(i -> { int result = intBuffer.get(i); log.info("result = {}", result); }); } }