javax.el.FactoryFinder Maven / Gradle / Ivy
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package javax.el;
import java.lang.reflect.Constructor;
import java.io.InputStream;
import java.io.File;
import java.io.FileInputStream;
import java.util.Properties;
import java.io.BufferedReader;
import java.io.InputStreamReader;
class FactoryFinder {
/**
* Creates an instance of the specified class using the specified
* ClassLoader object.
*
* @exception ELException if the given class could not be found
* or could not be instantiated
*/
private static Object newInstance(String className,
ClassLoader classLoader,
Properties properties)
{
try {
Class spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
spiClass = classLoader.loadClass(className);
}
if (properties != null) {
Constructor constr = null;
try {
constr = spiClass.getConstructor(Properties.class);
} catch (Exception ex) {
}
if (constr != null) {
return constr.newInstance(properties);
}
}
return spiClass.newInstance();
} catch (ClassNotFoundException x) {
throw new ELException(
"Provider " + className + " not found", x);
} catch (Exception x) {
throw new ELException(
"Provider " + className + " could not be instantiated: " + x,
x);
}
}
/**
* Finds the implementation Class object for the given
* factory name, or if that fails, finds the 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.
*
* @return the Class object of the specified message factory;
* may not be null
*
* @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; null to indicate that
* there is no fallback class name
* @exception ELException if there is an error
*/
static Object find(String factoryId, String fallbackClassName,
Properties properties)
{
ClassLoader classLoader;
try {
classLoader = Thread.currentThread().getContextClassLoader();
} catch (Exception x) {
throw new ELException(x.toString(), x);
}
String serviceId = "META-INF/services/" + factoryId;
// try to find services in CLASSPATH
try {
InputStream is=null;
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, properties);
}
}
} catch( Exception ex ) {
}
// try to read from $java.home/lib/el.properties
try {
String javah=System.getProperty( "java.home" );
String configFile = javah + File.separator +
"lib" + File.separator + "el.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, properties);
}
} catch(Exception ex ) {
}
// Use the system property
try {
String systemProp =
System.getProperty( factoryId );
if( systemProp!=null) {
return newInstance(systemProp, classLoader, properties);
}
} catch (SecurityException se) {
}
if (fallbackClassName == null) {
throw new ELException(
"Provider for " + factoryId + " cannot be found", null);
}
return newInstance(fallbackClassName, classLoader, properties);
}
}