javax.ws.rs.ext.FactoryFinder Maven / Gradle / Ivy
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package javax.ws.rs.ext;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Factory finder utility class.
*
* @author Paul Sandoz
* @author Marc Hadley
* @since 1.0
*/
final class FactoryFinder {
private static final Logger LOGGER = Logger.getLogger(FactoryFinder.class.getName());
private FactoryFinder() {
// prevents instantiation
}
static ClassLoader getContextClassLoader() {
return AccessController.doPrivileged(
new PrivilegedAction() {
@Override
public ClassLoader run() {
ClassLoader cl = null;
try {
cl = Thread.currentThread().getContextClassLoader();
} catch (SecurityException ex) {
LOGGER.log(
Level.WARNING,
"Unable to get context classloader instance.",
ex);
}
return cl;
}
});
}
/**
* Creates an instance of the specified class using the specified
* {@code ClassLoader} object.
*
* @param className name of the class to be instantiated.
* @param classLoader class loader to be used.
* @return instance of the specified class.
* @throws ClassNotFoundException if the given class could not be found
* or could not be instantiated.
*/
private static Object newInstance(final String className,
final ClassLoader classLoader) throws ClassNotFoundException {
try {
Class spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
try {
spiClass = Class.forName(className, false, classLoader);
} catch (ClassNotFoundException ex) {
LOGGER.log(
Level.FINE,
"Unable to load provider class " + className
+ " using custom classloader " + classLoader.getClass().getName()
+ " trying again with current classloader.",
ex);
spiClass = Class.forName(className);
}
}
return spiClass.newInstance();
} catch (ClassNotFoundException x) {
throw x;
} catch (Exception x) {
throw new ClassNotFoundException("Provider " + className + " could not be instantiated: " + x, x);
}
}
/**
* Finds the implementation {@code Class} object for the given
* factory name, or if that fails, finds the {@code Class} object
* for the given fallback class name. The arguments supplied MUST be
* used in order. If using the first argument is successful, the second
* one will not be used.
*
* This method is package private so that this code can be shared.
*
*
* @param factoryId the name of the factory to find, which is
* a system property.
* @param fallbackClassName the implementation class name, which is
* to be used only if nothing else.
* is found; {@code null} to indicate that
* there is no fallback class name.
* @return the {@code Class} object of the specified message factory;
* may not be {@code null}.
* @throws ClassNotFoundException if there is an error.
*/
static Object find(final String factoryId, final String fallbackClassName) throws ClassNotFoundException {
ClassLoader classLoader = getContextClassLoader();
String serviceId = "META-INF/services/" + factoryId;
// try to find services in CLASSPATH
try {
InputStream is;
if (classLoader == null) {
is = ClassLoader.getSystemResourceAsStream(serviceId);
} else {
is = classLoader.getResourceAsStream(serviceId);
}
if (is != null) {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));
String factoryClassName = rd.readLine();
rd.close();
if (factoryClassName != null && !"".equals(factoryClassName)) {
return newInstance(factoryClassName, classLoader);
}
}
} catch (Exception ex) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId + " from " + serviceId, ex);
}
// try to read from $java.home/lib/jaxrs.properties
try {
String javah = System.getProperty("java.home");
String configFile = javah + File.separator
+ "lib" + File.separator + "jaxrs.properties";
File f = new File(configFile);
if (f.exists()) {
Properties props = new Properties();
props.load(new FileInputStream(f));
String factoryClassName = props.getProperty(factoryId);
return newInstance(factoryClassName, classLoader);
}
} catch (Exception ex) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId
+ " from $java.home/lib/jaxrs.properties", ex);
}
// Use the system property
try {
String systemProp = System.getProperty(factoryId);
if (systemProp != null) {
return newInstance(systemProp, classLoader);
}
} catch (SecurityException se) {
LOGGER.log(Level.FINER, "Failed to load service " + factoryId
+ " from a system property", se);
}
if (fallbackClassName == null) {
throw new ClassNotFoundException(
"Provider for " + factoryId + " cannot be found", null);
}
return newInstance(fallbackClassName, classLoader);
}
}