享元模式指的是可以重复利用之前创建的对象。
比如，Long 的 valueOf
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| public static Long valueOf(long l) {
final int offset = 128;
if (l >= -128 && l <= 127) {
return LongCache.cache[(int)l + offset];
}
return new Long(l);
}
|
当 l 的值在 -128 到 127 之间的时候，会直接从缓存中返回，而不是创建新的。
案例 自定义连接池
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| package com.redisc;
import lombok.extern.slf4j.Slf4j;
import java.sql.*;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.*;
@Slf4j(topic = "c.Test")
public class Run {
public static void main(String[] args) throws InterruptedException {
Pool pool = new Pool(2);
for(int i = 0;i < 5;i++){
new Thread(() -> {
Connection connection = pool.borrow();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
pool.free(connection);
}).start();
}
}
}
@Slf4j(topic = "c.Pool")
class Pool {
// 连接池大小
private final int poolSize;
// 连接对象数组
private Connection[] connections;
// 连接状态数组 0 表示空闲 1 表示繁忙
private AtomicIntegerArray states;
//构造方法
public Pool(int poolSize) {
this.poolSize = poolSize;
this.connections = new Connection[poolSize];
this.states = new AtomicIntegerArray(new int[poolSize]);
for (int i = 0; i < poolSize; i++) {
connections[i] = new MockConnection();
}
}
// 连接
public Connection borrow() {
while (true) {
// 获取空闲连接
for (int i = 0; i < poolSize; i++) {
if (states.get(i) == 0) {
// 弄成线程安全的
if (states.compareAndSet(i, 0, 1)) {
log.debug("使用");
return connections[i];
}
}
}
// 如果没有空闲连接，当前线程进入等待
synchronized (this) {
try {
log.debug("等待");
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
// 归还链接
public void free(Connection connection) {
for (int i = 0; i < poolSize; i++) {
if (connections[i] == connection) {
log.debug("归还");
states.set(i, 0);
synchronized (this) {
log.debug("唤醒");
this.notifyAll();
}
break;
}
}
}
}
class MockConnection implements Connection {
...
}
|
输出
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| 21:05:21.246 [Thread-1] DEBUG c.Pool - 使用
21:05:21.246 [Thread-0] DEBUG c.Pool - 使用
21:05:21.246 [Thread-2] DEBUG c.Pool - 等待
21:05:21.250 [Thread-4] DEBUG c.Pool - 等待
21:05:21.250 [Thread-3] DEBUG c.Pool - 等待
21:05:22.250 [Thread-1] DEBUG c.Pool - 归还
21:05:22.250 [Thread-0] DEBUG c.Pool - 归还
21:05:22.250 [Thread-0] DEBUG c.Pool - 唤醒
21:05:22.250 [Thread-3] DEBUG c.Pool - 使用
21:05:22.250 [Thread-2] DEBUG c.Pool - 等待
21:05:22.250 [Thread-4] DEBUG c.Pool - 使用
21:05:22.250 [Thread-1] DEBUG c.Pool - 唤醒
21:05:22.250 [Thread-2] DEBUG c.Pool - 等待
21:05:23.253 [Thread-4] DEBUG c.Pool - 归还
21:05:23.253 [Thread-3] DEBUG c.Pool - 归还
21:05:23.253 [Thread-4] DEBUG c.Pool - 唤醒
21:05:23.253 [Thread-2] DEBUG c.Pool - 使用
21:05:23.253 [Thread-3] DEBUG c.Pool - 唤醒
21:05:24.258 [Thread-2] DEBUG c.Pool - 归还
21:05:24.258 [Thread-2] DEBUG c.Pool - 唤醒
|
