Java example source code file (ContextFinder.java)

This example Java source code file (ContextFinder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

bufferedreader, class, classloader, ioexception, jaxbcontext, jaxbexception, log, logging, map, meta\-inf\/services, net, properties, reflection, runtimeexception, security, string, trying, unable, url, util

The ContextFinder.java Java example source code

/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.xml.bind;

import java.util.Iterator;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.Map;
import java.util.Properties;
import java.util.StringTokenizer;
import java.util.logging.ConsoleHandler;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.security.AccessController;

import static javax.xml.bind.JAXBContext.JAXB_CONTEXT_FACTORY;


/**
 * This class is package private and therefore is not exposed as part of the
 * JAXB API.
 *
 * This code is designed to implement the JAXB 1.0 spec pluggability feature
 *
 * @author <ul>
Ryan Shoemaker, Sun Microsystems, Inc.
 * @see JAXBContext
 */
class ContextFinder {
    private static final Logger logger;
    static {
        logger = Logger.getLogger("javax.xml.bind");
        try {
            if (AccessController.doPrivileged(new GetPropertyAction("jaxb.debug")) != null) {
                // disconnect the logger from a bigger framework (if any)
                // and take the matters into our own hands
                logger.setUseParentHandlers(false);
                logger.setLevel(Level.ALL);
                ConsoleHandler handler = new ConsoleHandler();
                handler.setLevel(Level.ALL);
                logger.addHandler(handler);
            } else {
                // don't change the setting of this logger
                // to honor what other frameworks
                // have done on configurations.
            }
        } catch(Throwable t) {
            // just to be extra safe. in particular System.getProperty may throw
            // SecurityException.
        }
    }

    /**
     * If the {@link InvocationTargetException} wraps an exception that shouldn't be wrapped,
     * throw the wrapped exception.
     */
    private static void handleInvocationTargetException(InvocationTargetException x) throws JAXBException {
        Throwable t = x.getTargetException();
        if( t != null ) {
            if( t instanceof JAXBException )
                // one of our exceptions, just re-throw
                throw (JAXBException)t;
            if( t instanceof RuntimeException )
                // avoid wrapping exceptions unnecessarily
                throw (RuntimeException)t;
            if( t instanceof Error )
                throw (Error)t;
        }
    }


    /**
     * Determine if two types (JAXBContext in this case) will generate a ClassCastException.
     *
     * For example, (targetType)originalType
     *
     * @param originalType
     *          The Class object of the type being cast
     * @param targetType
     *          The Class object of the type that is being cast to
     * @return JAXBException to be thrown.
     */
    private static JAXBException handleClassCastException(Class originalType, Class targetType) {
        final URL targetTypeURL = which(targetType);

        return new JAXBException(Messages.format(Messages.ILLEGAL_CAST,
                // we don't care where the impl class is, we want to know where JAXBContext lives in the impl
                // class' ClassLoader
                getClassClassLoader(originalType).getResource("javax/xml/bind/JAXBContext.class"),
                targetTypeURL));
    }

    /**
     * Create an instance of a class using the specified ClassLoader
     */
    static JAXBContext newInstance( String contextPath,
                               String className,
                               ClassLoader classLoader,
                               Map properties )
        throws JAXBException {
        try {
            Class spFactory = safeLoadClass(className,classLoader);
            return newInstance(contextPath, spFactory, classLoader, properties);
        } catch (ClassNotFoundException x) {
            throw new JAXBException(
                Messages.format( Messages.PROVIDER_NOT_FOUND, className ),
                x);
        } catch (RuntimeException x) {
            // avoid wrapping RuntimeException to JAXBException,
            // because it indicates a bug in this code.
            throw x;
        } catch (Exception x) {
            // can't catch JAXBException because the method is hidden behind
            // reflection.  Root element collisions detected in the call to
            // createContext() are reported as JAXBExceptions - just re-throw it
            // some other type of exception - just wrap it
            throw new JAXBException(
                Messages.format( Messages.COULD_NOT_INSTANTIATE, className, x ),
                x);
        }
    }

    static JAXBContext newInstance( String contextPath,
                               Class spFactory,
                               ClassLoader classLoader,
                               Map properties )
        throws JAXBException
    {
        try {
            /*
             * javax.xml.bind.context.factory points to a class which has a
             * static method called 'createContext' that
             * returns a javax.xml.JAXBContext.
             */

            Object context = null;

            // first check the method that takes Map as the third parameter.
            // this is added in 2.0.
            try {
                Method m = spFactory.getMethod("createContext",String.class,ClassLoader.class,Map.class);
                // any failure in invoking this method would be considered fatal
                context = m.invoke(null,contextPath,classLoader,properties);
            } catch (NoSuchMethodException e) {
                // it's not an error for the provider not to have this method.
            }

            if(context==null) {
                // try the old method that doesn't take properties. compatible with 1.0.
                // it is an error for an implementation not to have both forms of the createContext method.
                Method m = spFactory.getMethod("createContext",String.class,ClassLoader.class);
                // any failure in invoking this method would be considered fatal
                context = m.invoke(null,contextPath,classLoader);
            }

            if(!(context instanceof JAXBContext)) {
                // the cast would fail, so generate an exception with a nice message
                throw handleClassCastException(context.getClass(), JAXBContext.class);
            }
            return (JAXBContext)context;
        } catch (InvocationTargetException x) {
            handleInvocationTargetException(x);
            // for other exceptions, wrap the internal target exception
            // with a JAXBException
            Throwable e = x;
            if(x.getTargetException()!=null)
                e = x.getTargetException();

            throw new JAXBException( Messages.format( Messages.COULD_NOT_INSTANTIATE, spFactory, e ), e );
        } catch (RuntimeException x) {
            // avoid wrapping RuntimeException to JAXBException,
            // because it indicates a bug in this code.
            throw x;
        } catch (Exception x) {
            // can't catch JAXBException because the method is hidden behind
            // reflection.  Root element collisions detected in the call to
            // createContext() are reported as JAXBExceptions - just re-throw it
            // some other type of exception - just wrap it
            throw new JAXBException(
                Messages.format( Messages.COULD_NOT_INSTANTIATE, spFactory, x ),
                x);
        }
    }


    /**
     * Create an instance of a class using the thread context ClassLoader
     */
    static JAXBContext newInstance(
                              Class[] classes,
                              Map properties,
                              String className) throws JAXBException {
        ClassLoader cl = getContextClassLoader();
        Class spi;
        try {
            spi = safeLoadClass(className,cl);
        } catch (ClassNotFoundException e) {
            throw new JAXBException(e);
        }

        if(logger.isLoggable(Level.FINE)) {
            // extra check to avoid costly which operation if not logged
            logger.log(Level.FINE, "loaded {0} from {1}", new Object[]{className, which(spi)});
        }

        return newInstance(classes, properties, spi);
    }

    static JAXBContext newInstance(Class[] classes,
                                   Map properties,
                                   Class spFactory) throws JAXBException {
        Method m;
        try {
            m = spFactory.getMethod("createContext", Class[].class, Map.class);
        } catch (NoSuchMethodException e) {
            throw new JAXBException(e);
        }
        try {
            Object context = m.invoke(null, classes, properties);
            if(!(context instanceof JAXBContext)) {
                // the cast would fail, so generate an exception with a nice message
                throw handleClassCastException(context.getClass(), JAXBContext.class);
            }
            return (JAXBContext)context;
        } catch (IllegalAccessException e) {
            throw new JAXBException(e);
        } catch (InvocationTargetException e) {
            handleInvocationTargetException(e);

            Throwable x = e;
            if (e.getTargetException() != null)
                x = e.getTargetException();

            throw new JAXBException(x);
        }
    }

    static JAXBContext find(String factoryId, String contextPath, ClassLoader classLoader, Map properties ) throws JAXBException {

        // TODO: do we want/need another layer of searching in $java.home/lib/jaxb.properties like JAXP?

        final String jaxbContextFQCN = JAXBContext.class.getName();

        // search context path for jaxb.properties first
        StringBuilder propFileName;
        StringTokenizer packages = new StringTokenizer( contextPath, ":" );
        String factoryClassName;

        if(!packages.hasMoreTokens())
            // no context is specified
            throw new JAXBException(Messages.format(Messages.NO_PACKAGE_IN_CONTEXTPATH));


        logger.fine("Searching jaxb.properties");

        while( packages.hasMoreTokens() ) {
            String packageName = packages.nextToken(":").replace('.','/');
            // com.acme.foo - > com/acme/foo/jaxb.properties
             propFileName = new StringBuilder().append(packageName).append("/jaxb.properties");

            Properties props = loadJAXBProperties( classLoader, propFileName.toString() );
            if (props != null) {
                if (props.containsKey(factoryId)) {
                    factoryClassName = props.getProperty(factoryId);
                    return newInstance( contextPath, factoryClassName, classLoader, properties );
                } else {
                    throw new JAXBException(Messages.format(Messages.MISSING_PROPERTY, packageName, factoryId));
                }
            }
        }

        logger.fine("Searching the system property");

        // search for a system property second (javax.xml.bind.JAXBContext)
        factoryClassName = AccessController.doPrivileged(new GetPropertyAction(JAXBContext.JAXB_CONTEXT_FACTORY));
        if(  factoryClassName != null ) {
            return newInstance( contextPath, factoryClassName, classLoader, properties );
        } else { // leave this here to assure compatibility
            factoryClassName = AccessController.doPrivileged(new GetPropertyAction(jaxbContextFQCN));
            if(  factoryClassName != null ) {
                return newInstance( contextPath, factoryClassName, classLoader, properties );
            }
        }

        // OSGi search
        Class jaxbContext = lookupJaxbContextUsingOsgiServiceLoader();
        if (jaxbContext != null) {
            logger.fine("OSGi environment detected");
            return newInstance(contextPath, jaxbContext, classLoader, properties);
        }

        logger.fine("Searching META-INF/services");
        // search META-INF services next
        BufferedReader r = null;
        try {
            final StringBuilder resource = new StringBuilder().append("META-INF/services/").append(jaxbContextFQCN);
            final InputStream resourceStream =
                    classLoader.getResourceAsStream(resource.toString());

            if (resourceStream != null) {
                r = new BufferedReader(new InputStreamReader(resourceStream, "UTF-8"));
                factoryClassName = r.readLine();
                if (factoryClassName != null) {
                    factoryClassName = factoryClassName.trim();
                }
                r.close();
                return newInstance(contextPath, factoryClassName, classLoader, properties);
            } else {
                logger.log(Level.FINE, "Unable to load:{0}", resource.toString());
            }
        } catch (UnsupportedEncodingException e) {
            // should never happen
            throw new JAXBException(e);
        } catch (IOException e) {
            throw new JAXBException(e);
        } finally {
            try {
                if (r != null) {
                    r.close();
                }
            } catch (IOException ex) {
                Logger.getLogger(ContextFinder.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

        // else no provider found
        logger.fine("Trying to create the platform default provider");
        return newInstance(contextPath, PLATFORM_DEFAULT_FACTORY_CLASS, classLoader, properties);
    }

    static JAXBContext find( Class[] classes, Map properties ) throws JAXBException {

        final String jaxbContextFQCN = JAXBContext.class.getName();
        String factoryClassName;

        // search for jaxb.properties in the class loader of each class first
        for (final Class c : classes) {
            // this classloader is used only to load jaxb.properties, so doing this should be safe.
            ClassLoader classLoader = getClassClassLoader(c);
            Package pkg = c.getPackage();
            if(pkg==null)
                continue;       // this is possible for primitives, arrays, and classes that are loaded by poorly implemented ClassLoaders
            String packageName = pkg.getName().replace('.', '/');

            // TODO: do we want to optimize away searching the same package?  org.Foo, org.Bar, com.Baz
            //       classes from the same package might come from different class loades, so it might be a bad idea

            // TODO: it's easier to look things up from the class
            // c.getResourceAsStream("jaxb.properties");

            // build the resource name and use the property loader code
            String resourceName = packageName+"/jaxb.properties";
            logger.log(Level.FINE, "Trying to locate {0}", resourceName);
            Properties props = loadJAXBProperties(classLoader, resourceName);
            if (props == null) {
                logger.fine("  not found");
            } else {
                logger.fine("  found");
                if (props.containsKey(JAXB_CONTEXT_FACTORY)) {
                    // trim() seems redundant, but adding to satisfy customer complaint
                    factoryClassName = props.getProperty(JAXB_CONTEXT_FACTORY).trim();
                    return newInstance(classes, properties, factoryClassName);
                } else {
                    throw new JAXBException(Messages.format(Messages.MISSING_PROPERTY, packageName, JAXB_CONTEXT_FACTORY));
                }
            }
        }

        // search for a system property second (javax.xml.bind.JAXBContext)
        logger.log(Level.FINE, "Checking system property {0}", JAXBContext.JAXB_CONTEXT_FACTORY);
        factoryClassName = AccessController.doPrivileged(new GetPropertyAction(JAXBContext.JAXB_CONTEXT_FACTORY));
        if (factoryClassName != null) {
            logger.log(Level.FINE, "  found {0}", factoryClassName);
            return newInstance( classes, properties, factoryClassName );
        } else { // leave it here for compatibility reasons
            logger.fine("  not found");
            logger.log(Level.FINE, "Checking system property {0}", jaxbContextFQCN);
            factoryClassName = AccessController.doPrivileged(new GetPropertyAction(jaxbContextFQCN));
            if (factoryClassName != null) {
                logger.log(Level.FINE, "  found {0}", factoryClassName);
                return newInstance( classes, properties, factoryClassName );
            } else {
                logger.fine("  not found");
            }
        }

        // OSGi search
        Class jaxbContext = lookupJaxbContextUsingOsgiServiceLoader();
        if (jaxbContext != null) {
            logger.fine("OSGi environment detected");
            return newInstance(classes, properties, jaxbContext);
        }

        // search META-INF services next
        logger.fine("Checking META-INF/services");
        BufferedReader r = null;
        try {
            final String resource = new StringBuilder("META-INF/services/").append(jaxbContextFQCN).toString();
            ClassLoader classLoader = getContextClassLoader();
            URL resourceURL;
            if(classLoader==null)
                resourceURL = ClassLoader.getSystemResource(resource);
            else
                resourceURL = classLoader.getResource(resource);

            if (resourceURL != null) {
                logger.log(Level.FINE, "Reading {0}", resourceURL);
                r = new BufferedReader(new InputStreamReader(resourceURL.openStream(), "UTF-8"));
                factoryClassName = r.readLine();
                if (factoryClassName != null) {
                    factoryClassName = factoryClassName.trim();
                }
                return newInstance(classes, properties, factoryClassName);
            } else {
                logger.log(Level.FINE, "Unable to find: {0}", resource);
            }
        } catch (UnsupportedEncodingException e) {
            // should never happen
            throw new JAXBException(e);
        } catch (IOException e) {
            throw new JAXBException(e);
        } finally {
            if (r != null) {
                try {
                    r.close();
                } catch (IOException ex) {
                    logger.log(Level.FINE, "Unable to close stream", ex);
                }
            }
        }

        // else no provider found
        logger.fine("Trying to create the platform default provider");
        return newInstance(classes, properties, PLATFORM_DEFAULT_FACTORY_CLASS);
    }

    private static Class lookupJaxbContextUsingOsgiServiceLoader() {
        try {
            // Use reflection to avoid having any dependency on ServiceLoader class
            Class target = Class.forName("com.sun.org.glassfish.hk2.osgiresourcelocator.ServiceLoader");
            Method m = target.getMethod("lookupProviderClasses", Class.class);
            Iterator iter = ((Iterable) m.invoke(null, JAXBContext.class)).iterator();
            return iter.hasNext() ? (Class)iter.next() : null;
        } catch(Exception e) {
            logger.log(Level.FINE, "Unable to find from OSGi: javax.xml.bind.JAXBContext");
            return null;
        }
    }

    private static Properties loadJAXBProperties( ClassLoader classLoader,
                                                  String propFileName )
        throws JAXBException {

        Properties props = null;

        try {
            URL url;
            if(classLoader==null)
                url = ClassLoader.getSystemResource(propFileName);
            else
                url = classLoader.getResource( propFileName );

            if( url != null ) {
                logger.log(Level.FINE, "loading props from {0}", url);
                props = new Properties();
                InputStream is = url.openStream();
                props.load( is );
                is.close();
            }
        } catch( IOException ioe ) {
            logger.log(Level.FINE,"Unable to load "+propFileName,ioe);
            throw new JAXBException( ioe.toString(), ioe );
        }

        return props;
    }


    /**
     * Search the given ClassLoader for an instance of the specified class and
     * return a string representation of the URL that points to the resource.
     *
     * @param clazz
     *          The class to search for
     * @param loader
     *          The ClassLoader to search.  If this parameter is null, then the
     *          system class loader will be searched
     * @return
     *          the URL for the class or null if it wasn't found
     */
    static URL which(Class clazz, ClassLoader loader) {

        String classnameAsResource = clazz.getName().replace('.', '/') + ".class";

        if(loader == null) {
            loader = getSystemClassLoader();
        }

        return loader.getResource(classnameAsResource);
    }

    /**
     * Get the URL for the Class from it's ClassLoader.
     *
     * Convenience method for {@link #which(Class, ClassLoader)}.
     *
     * Equivalent to calling: which(clazz, clazz.getClassLoader())
     *
     * @param clazz
     *          The class to search for
     * @return
     *          the URL for the class or null if it wasn't found
     */
    static URL which(Class clazz) {
        return which(clazz, getClassClassLoader(clazz));
    }

    /**
     * When JAXB is in J2SE, rt.jar has to have a JAXB implementation.
     * However, rt.jar cannot have META-INF/services/javax.xml.bind.JAXBContext
     * because if it has, it will take precedence over any file that applications have
     * in their jar files.
     *
     * <p>
     * When the user bundles his own JAXB implementation, we'd like to use it, and we
     * want the platform default to be used only when there's no other JAXB provider.
     *
     * <p>
     * For this reason, we have to hard-code the class name into the API.
     */
    private static final String PLATFORM_DEFAULT_FACTORY_CLASS = "com.sun.xml.internal.bind.v2.ContextFactory";

    /**
     * Loads the class, provided that the calling thread has an access to the class being loaded.
     */
    private static Class safeLoadClass(String className, ClassLoader classLoader) throws ClassNotFoundException {
       logger.log(Level.FINE, "Trying to load {0}", className);
       try {
          // make sure that the current thread has an access to the package of the given name.
          SecurityManager s = System.getSecurityManager();
          if (s != null) {
              int i = className.lastIndexOf('.');
              if (i != -1) {
                  s.checkPackageAccess(className.substring(0,i));
              }
          }

          if (classLoader == null) {
              return Class.forName(className);
          } else {
              return classLoader.loadClass(className);
          }
       } catch (SecurityException se) {
           // anyone can access the platform default factory class without permission
           if (PLATFORM_DEFAULT_FACTORY_CLASS.equals(className)) {
              return Class.forName(className);
           }
           throw se;
       }
    }

    private static ClassLoader getContextClassLoader() {
        if (System.getSecurityManager() == null) {
            return Thread.currentThread().getContextClassLoader();
        } else {
            return (ClassLoader) java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedAction() {
                        public java.lang.Object run() {
                            return Thread.currentThread().getContextClassLoader();
                        }
                    });
        }
    }

    private static ClassLoader getClassClassLoader(final Class c) {
        if (System.getSecurityManager() == null) {
            return c.getClassLoader();
        } else {
            return (ClassLoader) java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedAction() {
                        public java.lang.Object run() {
                            return c.getClassLoader();
                        }
                    });
        }
    }

    private static ClassLoader getSystemClassLoader() {
        if (System.getSecurityManager() == null) {
            return ClassLoader.getSystemClassLoader();
        } else {
            return (ClassLoader) java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedAction() {
                        public java.lang.Object run() {
                            return ClassLoader.getSystemClassLoader();
                        }
                    });
        }
    }

}