Eclipse Tomcat Plugin / Tickets / #17 DevLoader does not work on Tomcat 8.5.4

My solution:
package org.apache.catalina.loader;

import java.io.File;
import java.io.FileFilter;
import java.io.FileReader;
import java.io.IOException;
import java.io.LineNumberReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.StringTokenizer;

import javax.servlet.ServletContext;

import org.apache.catalina.Globals;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.util.ServerInfo;

public class DevLoader extends WebappLoader {

private static final String webClassPathFile = ".#webclasspath";
private static final String tomcatPluginFile = ".tomcatplugin";

public DevLoader() {
    super();        
}       
public DevLoader(ClassLoader parent) {
    super(parent);
}

/**

 * @see org.apache.catalina.Lifecycle#start()
 */
@Override
public void startInternal() throws LifecycleException {
    log("Starting DevLoader modified by Space008 (2016.09.09) for Tomcat 8.5: " + ServerInfo.getServerInfo());
    super.startInternal();

    ClassLoader cl = super.getClassLoader();
    if (!(cl instanceof WebappClassLoaderBase)) {
        logError("Unable to install WebappClassLoaderBase, received ClassLoader was " + cl.getClass() + "!");
        return;
    }
    WebappClassLoaderBase devCl = (WebappClassLoaderBase) cl;

    List<String> webClassPathEntries = readWebClassPathEntries();
    StringBuilder classpath   = new StringBuilder();
    for (Iterator<String> it = webClassPathEntries.iterator(); it.hasNext();) {
        String entry = it.next();
        File f = new File(entry);
        if (f.exists()) {
            if (f.isDirectory() && !entry.endsWith("/")) {
                f = new File(entry + "/");
            }
            try {
                URL url = f.toURL(); // f.toURI().toURL(); should be used since Java 8
                devCl.addURL(url);
                classpath.append(f.toString()).append(File.pathSeparatorChar);
                log("added to classpath: " + url.toString());
            } catch (MalformedURLException e) {
                logError(entry + " invalid (MalformedURL)");
            }
        } else {
            logError(entry + " does not exist !");
        }
    }

    String cp = (String)getServletContext().getAttribute(Globals.CLASS_PATH_ATTR);
    StringTokenizer tokenizer = new StringTokenizer(cp, File.pathSeparatorChar + "");
    while(tokenizer.hasMoreTokens()) {
        String token = tokenizer.nextToken();
        // only on windows 
        if (token.charAt(0)=='/' && token.charAt(2)==':') {
            token = token.substring(1);
        }
        classpath.append(token).append(File.pathSeparatorChar);
    }
    getServletContext().setAttribute(Globals.CLASS_PATH_ATTR, classpath.toString());
    log("class path for our application class loader = " + classpath);
}

protected void log(String msg) {
    System.out.println("[DevLoader] " + msg);
}
protected void logError(String msg) {
    System.err.println("[DevLoader] Error: " + msg);
}

protected List<String> readWebClassPathEntries() {
    List<String> rc = null;

    File prjDir = getProjectRootDir();
    if (prjDir == null) {
        return new ArrayList<>();
    }
    log("projectdir=" + prjDir.getAbsolutePath());

    rc = loadWebClassPathFile(prjDir);

    if (rc == null) rc = new ArrayList<String>(); // should not happen !
    return rc;
}

protected File getProjectRootDir() {
    File rootDir = getWebappDir();
    FileFilter filter = new FileFilter() {
        @Override
        public boolean accept(File file) {
            return (file.getName().equalsIgnoreCase(webClassPathFile) ||
                    file.getName().equalsIgnoreCase(tomcatPluginFile));
        }
    };
    while(rootDir != null) {
        File[] files = rootDir.listFiles(filter);
        if (files != null && files.length >= 1) {
            return files[0].getParentFile();
        }
        rootDir = rootDir.getParentFile();
    }
    return null;
}

protected List<String> loadWebClassPathFile(File prjDir) {
    File cpFile = new File(prjDir, webClassPathFile);
    if (cpFile.exists()) {          
        try (FileReader reader = new FileReader(cpFile); LineNumberReader lr = new LineNumberReader(reader)) {
            List<String> rc = new ArrayList<>();
            String line;
            while((line = lr.readLine()) != null) {
                line = line.replace('\\', '/');
                rc.add(line);
            }
            return rc;
        } catch(IOException ioEx) {
            return null;
        }           
    } else {
        return null;
    }
}

protected ServletContext getServletContext() {
    return getContext().getServletContext();
}

protected File getWebappDir() {     
    File webAppDir = new File(getServletContext().getRealPath("/"));
    return webAppDir;
}

}

I did the same patch before seeing the version above... Looks like I searched the wrong place!

Anyway, the problem comes from Tomcat 8.5.x (8.5.5 in my case) using a ParallelWebappClassLoader instead of a WebappClassLoader. However, both classes extend WebappClassLoaderBase, which defines the addURL() method required later in the startInternal() method.

By the way, while doing my own patch (which is similar to the one above including some Java 7 code optimization — looks like Georg Nepp and I had the same ideas), I configured the project to use Maven and I tricked my pom.xml file into generating a JAR identical in structure to the original, including the DevLoader.java source file. It you are interested in using Maven to facilitate dependency and build management, please tell me and I will provide you with my Maven project structure.

DevLoader does not work on Tomcat 8.5.4

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#17 DevLoader does not work on Tomcat 8.5.4

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