Java: Context ClassLoader加载器机制及spring boot打包运行可能导致类已存在，但运行时加载找不到

  System.out.println("java.sql.Connection :==>  " + Connection.class.getClassLoader());
  System.out.println("java.sql.DriverManager :==>  " + DriverManager.class.getClassLoader());
  System.out.println("java.sql.Driver :==>  " + Driver.class.getClassLoader());
  System.out.println("com.mysql.cj.jdbc.ConnectionImpl :==>  " + com.mysql.cj.jdbc.ConnectionImpl.class.getClassLoader());

java.lang.Class#forName(java.lang.String, boolean, java.lang.ClassLoader)

java.lang.Thread#getContextClassLoader

java.sql.DriverManager#ensureDriversInitialized

 ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class);
                    Iterator<Driver> driversIterator = loadedDrivers.iterator();

                    /* Load these drivers, so that they can be instantiated.
                     * It may be the case that the driver class may not be there
                     * i.e. there may be a packaged driver with the service class
                     * as implementation of java.sql.Driver but the actual class
                     * may be missing. In that case a java.util.ServiceConfigurationError
                     * will be thrown at runtime by the VM trying to locate
                     * and load the service.
                     *
                     * Adding a try catch block to catch those runtime errors
                     * if driver not available in classpath but it's
                     * packaged as service and that service is there in classpath.
                     */
                    try {
                        while (driversIterator.hasNext()) {
                            driversIterator.next();
                        }
                    } catch (Throwable t) {
                        // Do nothing
                    }
                    return null;

public static <S> ServiceLoader<S> load(Class<S> service) {
        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        return new ServiceLoader<>(Reflection.getCallerClass(), service, cl);
    }

Thread.currentThread().getContextClassLoader();

java.lang.Class#forName(java.lang.String, boolean, java.lang.ClassLoader)

package com.example.demo;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.util.concurrent.*;

/**
 * @author 认知科技技术团队
 * 微信公众号：认知科技技术团队
 */
@Component
@Slf4j
public class ThreadPoolConfig {

    @PostConstruct
    void init() throws ExecutionException, InterruptedException {
        log.info("当前类加载器:{}", getClass().getClassLoader());
        log.info("启动类加载器:{}", Demo1Application.class.getClassLoader());
        log.info("{} ===> {}", "Thread.currentThread().getContextClassLoader", Thread.currentThread().getContextClassLoader());

        Thread thread = new Thread(
                () ->
                        log.info("Thread: {} ===> {}", "Thread.currentThread().getContextClassLoader",
                                Thread.currentThread().getContextClassLoader())
        );

        thread.start();
        thread.join();

        //CompletableFuture 默认线程池注意上下文类加载器
        CompletableFuture<Void> future = CompletableFuture.runAsync(
                () ->
                        log.info("CompletableFuture: {} ===> {}", "Thread.currentThread().getContextClassLoader",
                                Thread.currentThread().getContextClassLoader())
        );
        future.get();

    }

}

org.springframework.boot.loader.LaunchedURLClassLoader

java version "17.0.2" 2022-01-18 LTS
Java(TM) SE Runtime Environment (build 17.0.2+8-LTS-86)
Java HotSpot(TM) 64-Bit Server VM (build 17.0.2+8-LTS-86, mixed mode, sharing)

        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.7</version>