Struts example source code file (ReloadingClassLoader.java)

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

Java - Struts tags/keywords

classloader, classloader, exception, io, net, network, regex, reloading, reloadingclassloader, resourcestore, resourcestore, resourcestoreclassloader, resourcestoreclassloader, runtimeexception, unable, url, url, util, xworkexception

The Struts ReloadingClassLoader.java source code

/*
 * Copyright 2002-2006,2009 The Apache Software Foundation.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.opensymphony.xwork2.util.classloader;

import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;
import com.opensymphony.xwork2.util.classloader.FileResourceStore;
import com.opensymphony.xwork2.util.URLUtil;
import com.opensymphony.xwork2.XWorkException;

import java.io.InputStream;
import java.io.File;
import java.net.URL;
import java.net.URISyntaxException;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.Set;
import java.util.Collections;
import java.util.Collection;
import java.util.HashSet;

import org.apache.commons.lang.ObjectUtils;

/**
 * The ReloadingClassLoader uses a delegation mechanism to allow
 * classes to be reloaded. That means that loadClass calls may
 * return different results if the class was changed in the underlying
 * ResourceStore.
 * <p/>
 * class taken from Apache JCI
 */
public class ReloadingClassLoader extends ClassLoader {
    private static final Logger LOG = LoggerFactory.getLogger(ReloadingClassLoader.class);
    private final ClassLoader parent;
    private ResourceStore[] stores;
    private ClassLoader delegate;

    private Set<Pattern> acceptClasses = Collections.emptySet();

    public ReloadingClassLoader(final ClassLoader pParent) {
        super(pParent);
        parent = pParent;
        URL parentRoot = pParent.getResource("");
        URL root = URLUtil.normalizeToFileProtocol(parentRoot);
        root = (URL) ObjectUtils.defaultIfNull(root, parentRoot);
        try {
            if (root != null) {
                stores = new ResourceStore[]{new FileResourceStore(new File(root.toURI()))};
            } else {
                throw new XWorkException("Unable to start the reloadable class loader, consider setting 'struts.convention.classes.reload' to false");
            }
        } catch (URISyntaxException e) {
            throw new XWorkException("Unable to start the reloadable class loader, consider setting 'struts.convention.classes.reload' to false", e);
        } catch (RuntimeException e) {
            // see WW-3121
            // TODO: Fix this for a reloading mechanism to be marked as stable
            if (root != null)
                LOG.error("Exception while trying to build the ResourceStore for URL [#0]", e, root.toString());
            else
                LOG.error("Exception while trying to get root resource from class loader", e);
            LOG.error("Consider setting struts.convention.classes.reload=false");
            throw e;
        }

        delegate = new ResourceStoreClassLoader(parent, stores);
    }

    public boolean addResourceStore(final ResourceStore pStore) {
        try {
            final int n = stores.length;
            final ResourceStore[] newStores = new ResourceStore[n + 1];
            System.arraycopy(stores, 0, newStores, 1, n);
            newStores[0] = pStore;
            stores = newStores;
            delegate = new ResourceStoreClassLoader(parent, stores);
            return true;
        } catch (final RuntimeException e) {
            LOG.error("Could not add resource store", e);
        }
        return false;
    }

    public boolean removeResourceStore(final ResourceStore pStore) {

        final int n = stores.length;
        int i = 0;

        // FIXME: this should be improved with a Map
        // find the pStore and index position with var i
        while ((i < n) && (stores[i] != pStore)) {
            i++;
        }

        // pStore was not found
        if (i == n) {
            return false;
        }

        // if stores length > 1 then array copy old values, else create new empty store
        final ResourceStore[] newStores = new ResourceStore[n - 1];
        if (i > 0) {
            System.arraycopy(stores, 0, newStores, 0, i);
        }
        if (i < n - 1) {
            System.arraycopy(stores, i + 1, newStores, i, (n - i - 1));
        }

        stores = newStores;
        delegate = new ResourceStoreClassLoader(parent, stores);
        return true;
    }

    public void reload() {
        if (LOG.isTraceEnabled())
            LOG.trace("Reloading class loader");
        delegate = new ResourceStoreClassLoader(parent, stores);
    }

    public void clearAssertionStatus() {
        delegate.clearAssertionStatus();
    }

    public URL getResource(String name) {
        return delegate.getResource(name);
    }

    public InputStream getResourceAsStream(String name) {
        return delegate.getResourceAsStream(name);
    }

    public Class loadClass(String name) throws ClassNotFoundException {
        return isAccepted(name) ? delegate.loadClass(name) : parent.loadClass(name);
    }

    public void setClassAssertionStatus(String className, boolean enabled) {
        delegate.setClassAssertionStatus(className, enabled);
    }

    public void setDefaultAssertionStatus(boolean enabled) {
        delegate.setDefaultAssertionStatus(enabled);
    }

    public void setPackageAssertionStatus(String packageName, boolean enabled) {
        delegate.setPackageAssertionStatus(packageName, enabled);
    }

    public void setAccepClasses(Set<Pattern> acceptClasses) {
        this.acceptClasses = acceptClasses;
    }

    protected boolean isAccepted(String className) {
        if (!this.acceptClasses.isEmpty()) {
            for (Pattern pattern : acceptClasses) {
                Matcher matcher = pattern.matcher(className);
                if (matcher.matches()) {
                    return true;
                }
            }
            return false;
        } else
            return true;
    }
}