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FactoryFinder.javaAPI DocJava SE 6 API10930Tue Jun 10 00:27:12 BST 2008javax.xml.transform

FactoryFinder

public class FactoryFinder extends Object

Implements pluggable Datatypes.

This class is duplicated for each JAXP subpackage so keep it in sync. It is package private for secure class loading.

author
Santiago.PericasGeertsen@sun.com

Fields Summary
private static boolean
debug
Internal debug flag.
static Properties
cacheProps
Cache for properties in java.home/lib/jaxp.properties
static boolean
firstTime
Flag indicating if properties from java.home/lib/jaxp.properties have been cached.
static SecuritySupport
ss
Security support class use to check access control before getting certain system resources.
Constructors Summary
Methods Summary
private static voiddPrint(java.lang.String msg)


    // Define system property "jaxp.debug" to get output
     
        // Use try/catch block to support applets, which throws
        // SecurityException out of this code.
        try {
            String val = ss.getSystemProperty("jaxp.debug");
            // Allow simply setting the prop to turn on debug
            debug = val != null && !"false".equals(val);
        } 
        catch (SecurityException se) {
            debug = false;
        }
    
        if (debug) {
            System.err.println("JAXP: " + msg);
        }
static java.lang.Objectfind(java.lang.String factoryId, java.lang.String fallbackClassName)
Finds the implementation Class object in the specified order. Main entry point.

return
Class object of factory, never null
param
factoryId Name of the factory to find, same as a property name
param
fallbackClassName Implementation class name, if nothing else is found. Use null to mean no fallback. Package private so this code can be shared.

        
        dPrint("find factoryId =" + factoryId);
        
        // Use the system property first
        try {
            String systemProp = ss.getSystemProperty(factoryId);
            if (systemProp != null) {                
                dPrint("found system property, value=" + systemProp);
                return newInstance(systemProp, null, true);
            }
        } 
        catch (SecurityException se) {
            if (debug) se.printStackTrace();
        }

        // try to read from $java.home/lib/jaxp.properties
        try {
            String factoryClassName = null;
            if (firstTime) {
                synchronized (cacheProps) {
                    if (firstTime) {
                        String configFile = ss.getSystemProperty("java.home") + File.separator +
                            "lib" + File.separator + "jaxp.properties";
                        File f = new File(configFile);
                        firstTime = false;
                        if (ss.doesFileExist(f)) {
                            dPrint("Read properties file "+f);
                            cacheProps.load(ss.getFileInputStream(f));
                        }
                    }
                }
            }
            factoryClassName = cacheProps.getProperty(factoryId);            

            if (factoryClassName != null) {
                dPrint("found in $java.home/jaxp.properties, value=" + factoryClassName);
                return newInstance(factoryClassName, null, true);
            }
        } 
        catch (Exception ex) {
            if (debug) ex.printStackTrace();
        }

        // Try Jar Service Provider Mechanism
        Object provider = findJarServiceProvider(factoryId);
        if (provider != null) {
            return provider;
        }
        if (fallbackClassName == null) {
            throw new ConfigurationError(
                "Provider for " + factoryId + " cannot be found", null);
        }

        dPrint("loaded from fallback value: " + fallbackClassName);
        return newInstance(fallbackClassName, null, true);
private static java.lang.ObjectfindJarServiceProvider(java.lang.String factoryId)

        String serviceId = "META-INF/services/" + factoryId;
        InputStream is = null;
        
        // First try the Context ClassLoader
        ClassLoader cl = ss.getContextClassLoader();
        if (cl != null) {
            is = ss.getResourceAsStream(cl, serviceId);
            
            // If no provider found then try the current ClassLoader
            if (is == null) {
                cl = FactoryFinder.class.getClassLoader();                
                is = ss.getResourceAsStream(cl, serviceId);
            }
        } else {
            // No Context ClassLoader, try the current ClassLoader
            cl = FactoryFinder.class.getClassLoader();
            is = ss.getResourceAsStream(cl, serviceId);
        }
        
        if (is == null) {
            // No provider found
            return null;
        }
        
        if (debug) {    // Extra check to avoid computing cl strings
            dPrint("found jar resource=" + serviceId + " using ClassLoader: " + cl);
        }
        
        BufferedReader rd;
        try {
            rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));
        } 
        catch (java.io.UnsupportedEncodingException e) {
            rd = new BufferedReader(new InputStreamReader(is));
        }
        
        String factoryClassName = null;
        try {
            // XXX Does not handle all possible input as specified by the
            // Jar Service Provider specification
            factoryClassName = rd.readLine();
            rd.close();
        } catch (IOException x) {
            // No provider found
            return null;
        }
        
        if (factoryClassName != null && !"".equals(factoryClassName)) {
            dPrint("found in resource, value=" + factoryClassName);
            
            // Note: here we do not want to fall back to the current
            // ClassLoader because we want to avoid the case where the
            // resource file was found using one ClassLoader and the
            // provider class was instantiated using a different one.
            return newInstance(factoryClassName, cl, false);
        }
        
        // No provider found
        return null;
private static java.lang.ClassgetProviderClass(java.lang.String className, java.lang.ClassLoader cl, boolean doFallback)
Attempt to load a class using the class loader supplied. If that fails and fall back is enabled, the current (i.e. bootstrap) class loader is tried. If the class loader supplied is null, first try using the context class loader followed by the current (i.e. bootstrap) class loader.

        try {
            if (cl == null) {
                cl = ss.getContextClassLoader();
                if (cl == null) {
                    throw new ClassNotFoundException();
                }
                else {
                    return cl.loadClass(className);
                }
            } 
            else {
                return cl.loadClass(className);
            }
        }
        catch (ClassNotFoundException e1) {
            if (doFallback) {
                // Use current class loader - should always be bootstrap CL
                return Class.forName(className, true, FactoryFinder.class.getClassLoader());
            } 
            else {
                throw e1;
            }
        }
static java.lang.ObjectnewInstance(java.lang.String className, java.lang.ClassLoader cl, boolean doFallback)
Create an instance of a class. Delegates to method getProviderClass() in order to load the class.

param
className Name of the concrete class corresponding to the service provider
param
cl ClassLoader to use to load the class, null means to use the bootstrap ClassLoader
param
doFallback True if the current ClassLoader should be tried as a fallback if the class is not found using cl

        try {
            Class providerClass = getProviderClass(className, cl, doFallback);                        
            Object instance = providerClass.newInstance();
            if (debug) {    // Extra check to avoid computing cl strings
                dPrint("created new instance of " + providerClass +
                       " using ClassLoader: " + cl);
            }
            return instance;
        } 
        catch (ClassNotFoundException x) {
            throw new ConfigurationError(
                "Provider " + className + " not found", x);
        } 
        catch (Exception x) {
            throw new ConfigurationError(
                "Provider " + className + " could not be instantiated: " + x,
                x);
        }