Jvm: thread context classloader

One 、 When the context class loader is not actively set , The thread context class loader is the application class loader (AppClassLoader)

1. introduce MySQL package

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.30</version>
        </dependency>

2. test ThreadContextClassLoader

package cn.edu.tju;

import java.sql.Driver;
import java.util.Iterator;
import java.util.ServiceLoader;

public class ThreadContextClassLoaderTest {
    public static void main(String[] args) {
        ServiceLoader<Driver> serviceLoader=ServiceLoader.load(Driver.class);
        Iterator<Driver> iterator = serviceLoader.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next().getClass());
        }
    }
}

3. Operation output ：

4. Result analysis ： Because there are no settings ThreadContexClassLoader, So the main thread ThreadContextClassLoader by AppClassLoader, It can be loaded from the application's classpath MySQL Of the two Driver class .

5. Modify main class ：

package cn.edu.tju;

import java.sql.Driver;
import java.util.Iterator;
import java.util.ServiceLoader;

public class ThreadContextClassLoaderTest {
    public static void main(String[] args) {
        Thread.currentThread().setContextClassLoader(SpiTest.class.getClassLoader().getParent());
        
        ServiceLoader<Driver> serviceLoader=ServiceLoader.load(Driver.class);
        Iterator<Driver> iterator = serviceLoader.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next().getClass());
        }
    }
}

Change the context class loader of the thread to AppClassLoader Of parent namely ExtClassLoader, Will not be able to load... Under the classpath MySQL Of Driver class , therefore , The program runs without output