java基础--JDK SPI概述

package org.xrq.test.spi;

public interface SpiService {

    public void hello();
    
}

package org.xrq.test.spi;

public class SpiServiceA implements SpiService {

    public void hello() {
        System.out.println("SpiServiceA.Hello");
    }
    
}

package org.xrq.test.spi;

public class SpiServiceB implements SpiService {

    @Override
    public void hello() {
        System.out.println("SpiServiceB.hello");
    }
    
}

public class SpiTest {

    @Test
    public void testSpi() {
        ServiceLoader<SpiService> serviceLoader = ServiceLoader.load(SpiService.class);
        
        Iterator<SpiService> iterator = serviceLoader.iterator();
        while (iterator.hasNext()) {
            SpiService spiService = iterator.next();
            
            spiService.hello();
        }
    }
    
}

public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    //
    // Register ourselves with the DriverManager
    //
    static {
        try {
            java.sql.DriverManager.registerDriver(new Driver());
        } catch (SQLException E) {
            throw new RuntimeException("Can't register driver!");
        }
    }

    /**
     * Construct a new driver and register it with DriverManager
     * 
     * @throws SQLException
     *             if a database error occurs.
     */
    public Driver() throws SQLException {
        // Required for Class.forName().newInstance()
    }
}

public static synchronized void registerDriver(java.sql.Driver driver, DriverAction da)
      throws SQLException {

    /* Register the driver if it has not already been added to our list */
    if(driver != null) {
        registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
    } else {
        // This is for compatibility with the original DriverManager
        throw new NullPointerException();
    }

    println("registerDriver: " + driver);

}

/**
 * Load the initial JDBC drivers by checking the System property
 * jdbc.properties and then use the {@code ServiceLoader} mechanism
 */
static {
    loadInitialDrivers();
    println("JDBC DriverManager initialized");
}

AccessController.doPrivileged(new PrivilegedAction<Void>() {
    public Void run() {

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

        /* 
         * 节约篇幅，注释省略
         */
        try{
            while(driversIterator.hasNext()) {
               driversIterator.next();
            }
        } catch(Throwable t) {
        // Do nothing
        }
        return null;
    }
});

private S nextService() {
    if (!hasNextService())
        throw new NoSuchElementException();
    String cn = nextName;
    nextName = null;
    Class<?> c = null;
    try {
        c = Class.forName(cn, false, loader);
    } catch (ClassNotFoundException x) {
        fail(service,
             "Provider " + cn + " not found");
   }
    if (!service.isAssignableFrom(c)) {
       fail(service,
             "Provider " + cn  + " not a subtype");
    }
    try {
        S p = service.cast(c.newInstance());
        providers.put(cn, p);
        return p;
    } catch (Throwable x) {
        fail(service,
             "Provider " + cn + " could not be instantiated",
            x);
    }
    throw new Error();          // This cannot happen
}