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);
});
}
}
