Java中常用的设计模式之单例模式详解

package com.asurplus.common.singleton.style1;
import lombok.extern.slf4j.Slf4j;
import java.util.Objects;
@Slf4j
public class ResUtils {
    private volatile static ResUtils instance = null;
    /**
     * 私有的构造方法
     */
    private ResUtils() {
    }
    /**
     * 提供获取实例的方法
     *
     * @return
     */
    public static ResUtils getInstance() {
        // 为空才创建
        if (Objects.isNull(instance)) {
            // 避免并发操作时
            synchronized (ResUtils.class) {
                // 为空才创建
                if (Objects.isNull(instance)) {
                    // 创建新对象
                    instance = new ResUtils();
                    log.info("创建了对象");
                }
            }
        }
        return instance;
    }
}

package com.asurplus.common.singleton.style2;
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class ResUtils2 {
    /**
     * 静态内部类
     */
    private static class ResUtils2Holder {
        private static ResUtils2 instance = new ResUtils2();
    }
    /**
     * 提供获取实例的方法
     *
     * @return
     */
    public static ResUtils2 getInstance() {
        return ResUtils2Holder.instance;
    }
}

package com.asurplus.common.singleton;
import com.asurplus.common.singleton.style1.ResUtils;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
 * 单例模式
 */
public class TestMain {
    public static void main(String[] args) {
        // 创建线程池
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 100; i++) {
            executorService.execute(ResUtils::getInstance);
        }
        executorService.shutdown();
    }
}