JDK13Services.java 文件源码

/** Obtain the value of a default provider property.
    @param typeClass The type of the default provider property. This
    should be one of Receiver.class, Transmitter.class, Sequencer.class,
    Synthesizer.class, SourceDataLine.class, TargetDataLine.class,
    Clip.class or Port.class.
    @return The complete value of the property, if available.
    If the property is not set, null is returned.
 */
private static synchronized String getDefaultProvider(Class typeClass) {
    if (!SourceDataLine.class.equals(typeClass)
            && !TargetDataLine.class.equals(typeClass)
            && !Clip.class.equals(typeClass)
            && !Port.class.equals(typeClass)
            && !Receiver.class.equals(typeClass)
            && !Transmitter.class.equals(typeClass)
            && !Synthesizer.class.equals(typeClass)
            && !Sequencer.class.equals(typeClass)) {
        return null;
    }
    String name = typeClass.getName();
    String value = AccessController.doPrivileged(
            (PrivilegedAction<String>) () -> System.getProperty(name));
    if (value == null) {
        value = getProperties().getProperty(name);
    }
    if ("".equals(value)) {
        value = null;
    }
    return value;
}