Classpath resource reader

Keep in mind that this is just prototype code. I was just figuring out how I was going to do something. My intention is to throw this away, and then implement it for real.

There is a full code walkthrough at the end.

This prototype code for reading deeply nested classpath resources. If you wanted to read all files that started with foo and ended with .txt, under /foo/bar/resources/ everywhere on the classpath sort of thing.


 

package com.foo;

import java.io.File;
import java.io.FileReader;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URI;
import java.net.URL;
import java.util.Enumeration;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;

/**
 * Prototype resource reader.
 * This prototype is devoid of error checking.
 *
 * 
 * I have two prototype jar files that I have setup.
 * 
 *             
 *                  invoke
 *                  invoke
 *                  1.0-SNAPSHOT
 *              
 *
 *              
 *                   node
 *                   node
 *                   1.0-SNAPSHOT
 *              
 * 
* 
 * The jar files each have a file under /org/node/ called resource.txt.
 * 
 * This is just a prototype of what a handler would look like with classpath://
 * I also have a resource.foo.txt in my local resources for this project.
 */
public class ClasspathReader {

    public static void main(String[] args) throws Exception {

        String namespace = "resource";

        //someResource is classpath.
        String someResource = args.length > 0 ? args[0] :
                //"classpath:///org/node/resource.txt";   It works with files
                "classpath:///org/node/";                 //It also works with directories

        URI someResourceURI = URI.create(someResource);

        System.out.println("URI of resource = " + someResourceURI);

        someResource = someResourceURI.getPath();

        System.out.println("PATH of resource =" + someResource);

        boolean isDir = !someResource.endsWith(".txt");


        // Classpath resource can never really start with a starting slash.
        //   Logically they do, but in reality you have to strip it.
        //   This is a known behavior of classpath resources.
        //   It works with a slash unless the resource is in a jar file.
        //   Bottom line, by stripping it, it always works.

        if (someResource.startsWith("/")) {
            someResource = someResource.substring(1);
        }

        // Use the ClassLoader to lookup all resources that have this name.
        // Look for all resources that match the location we are looking for.
        Enumeration resources =  null;

        // Check the context classloader first. Always use this if available.
        try {
            resources =    Thread.currentThread().getContextClassLoader().getResources(someResource);
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        if (resources==null || !resources.hasMoreElements()) {
            resources = ClasspathReader.class.getClassLoader().getResources(someResource);
        }

        //Now iterate over the URLs of the resources from the classpath
        while (resources.hasMoreElements()) {
            URL resource = resources.nextElement();


            // if the resource is a file, it just means that we can use normal mechnism
            // to scan the directory.
 
            if (resource.getProtocol().equals("file")) {
                //if it is a file then we can handle it the normal way.
                handleFile(resource, namespace);
                continue;
            }

            System.out.println("Resource " + resource);
            //
            //  Split up the string that looks like this:
            //  jar:file:/Users/rick/.m2/repository/invoke/invoke/1.0-SNAPSHOT/invoke-1.0-SNAPSHOT.jar!/org/node/
            //  into
            //     this /Users/rick/.m2/repository/invoke/invoke/1.0-SNAPSHOT/invoke-1.0-SNAPSHOT.jar
            //   and this
            //          /org/node/
           
            String[] split = resource.toString().split(":");
            String[] split2 = split[2].split("!");
            String zipFileName = split2[0];
            String sresource = split2[1];

            System.out.printf("After split zip file name = %s," +
                    " \nresource in zip %s \n", zipFileName, sresource);


            // Open up the zip file. 
            ZipFile zipFile = new ZipFile(zipFileName);


            //  Iterate through the entries.  
            Enumeration entries = zipFile.entries();

            while (entries.hasMoreElements()) {
                ZipEntry entry = entries.nextElement();
                // If it is a directory, then skip it.
                if (entry.isDirectory()) {
                    continue;
                }

                String entryName = entry.getName();
                System.out.printf("zip entry name %s \n", entryName);

                // If it does not start with our someResource String
                // then it is not our resource so continue.
                if (!entryName.startsWith(someResource)) {
                    continue;
                }


                // the fileName part from the entry name.
                // where /foo/bar/foo/bee/bar.txt, bar.txt is the file
                //
                String fileName = entryName.substring(entryName.lastIndexOf("/") + 1);
                System.out.printf("fileName %s \n", fileName);

                // See if the file starts with our namespace and ends with our extension.
                if (fileName.startsWith(namespace) && fileName.endsWith(".txt")) {

                    // If you found the file, print out the contents of the file to System.out.
                    try (Reader reader = new InputStreamReader(zipFile.getInputStream(entry))) {
                        StringBuilder builder = new StringBuilder();
                        int ch = 0;
                        while ((ch = reader.read()) != -1) {
                            builder.append((char) ch);

                        }
                        System.out.printf("zip fileName = %s\n\n####\n contents of file %s\n###\n", entryName, builder);
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }
                }

            }

        }


    }

    /** The file was on the file system not a zip file,
     * this is here for completeness for this example.
     * otherwise.
     * @param resource
     * @param namespace
     * @throws Exception
     */
    private static void handleFile(URL resource, String namespace) throws Exception {
        System.out.println("Handle this resource as a file " + resource);
        URI uri = resource.toURI();
        File file = new File(uri.getPath());


        if (file.isDirectory()) {
            for (File childFile : file.listFiles()) {
                if (childFile.isDirectory()) {
                    continue;
                }
                String fileName = childFile.getName();
                if (fileName.startsWith(namespace) && fileName.endsWith("txt")) {

                    try (FileReader reader = new FileReader(childFile)) {
                        StringBuilder builder = new StringBuilder();
                        int ch = 0;
                        while ((ch = reader.read()) != -1) {
                            builder.append((char) ch);

                        }
                        System.out.printf("fileName = %s\n\n####\n contents of file %s\n###\n", childFile, builder);
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }

                }

            }
        } else {
            String fileName = file.getName();
            if (fileName.startsWith(namespace) && fileName.endsWith("txt")) {

                try (FileReader reader = new FileReader(file)) {
                    StringBuilder builder = new StringBuilder();
                    int ch = 0;
                    while ((ch = reader.read()) != -1) {
                        builder.append((char) ch);

                    }
                    System.out.printf("fileName = %s\n\n####\n contents of file %s\n###\n", fileName, builder);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }

            }

        }
    }

}

Further thoughts....

You could get all of the resources (all jar files on classpath should work even one without classes):

    Enumeration<URL> resources = null;
    try {
        resources = Thread.currentThread().getContextClassLoader().getResources(someResource);
    } catch (Exception ex) {
         //no op      
    }
    if (resources == null || !resources.hasMoreElements()) {
        resources = ClasspathReader.class.getClassLoader().getResources(someResource);
    }

Then check to see if the current resource is a file. Files you can deal with direct as files. But your question was about jar files so I wont go there.

    while (resources.hasMoreElements()) {
        URL resource = resources.nextElement();


        if (resource.getProtocol().equals("file")) {
            //if it is a file then we can handle it the normal way.
            handleFile(resource, namespace);
            continue;
        }

At this point you should have only jar:file resources so... Split up the string that looks like this:

jar:file:/Users/rick/.m2/repository/invoke/invoke/1.0-SNAPSHOT/invoke-1.0-SNAPSHOT.jar!/org/node/

into this

/Users/rick/.m2/repository/invoke/invoke/1.0-SNAPSHOT/invoke-1.0-SNAPSHOT.jar

and this

/org/node/

Here is the code to do the above devoid of pesky error checking. :)

        String[] split = resource.toString().split(":");
        String[] split2 = split[2].split("!");
        String zipFileName = split2[0];
        String sresource = split2[1];

        System.out.printf("After split zip file name = %s," +
                " \nresource in zip %s \n", zipFileName, sresource);

Now we have the zip file name so we can read it:

        ZipFile zipFile = new ZipFile(zipFileName);

Now we can iterate through its entries:

        Enumeration<? extends ZipEntry> entries = zipFile.entries();

        while (entries.hasMoreElements()) {
            ZipEntry entry = entries.nextElement();

            /* If it is a directory, then skip it. */
            if (entry.isDirectory()) {
                continue;
            }

            String entryName = entry.getName();
            System.out.printf("zip entry name %s \n", entryName);

See if it starts with the resource we are looking for.

            if (!entryName.startsWith(someResource)) {
                continue;
            }

There were two tricks I did earlier to see if it was a directory

    boolean isDir = !someResource.endsWith(".txt");

This only works because I am looking for resources that ends with .txt and I assume if it does not end with .txt that it is an dir /foo/dir and /foo/dir/ both work.

The other trick was this:

    if (someResource.startsWith("/")) {
        someResource = someResource.substring(1);
    }

Classpath resource can never really start with a starting slash. Logically they do, but in reality you have to strip it. This is a known behavior of classpath resources. It works with a slash unless the resource is in a jar file. Bottom line, by stripping it, it always works.

We need to get the actual fileName of the darn thing. The fileName part from the entry name. where /foo/bar/foo/bee/bar.txt, and we want 'bar.txt' which is the fileName. Back inside of our while loop.

        while (entries.hasMoreElements()) {
            ZipEntry entry = entries.nextElement();
            ...
            String entryName = entry.getName(); //entry is zipEntry
            String fileName = entryName.substring(entryName.lastIndexOf("/") + 1);


            /** See if the file starts with our namespace and ends with our extension. */
            if (fileName.startsWith(namespace) && fileName.endsWith(".txt")) {

Next we see if these entry matches our criteria and if so read contents of the file to System.out.

          try (Reader reader = new InputStreamReader(zipFile.getInputStream(entry))) {
                    StringBuilder builder = new StringBuilder();
                    int ch = 0;
                    while ((ch = reader.read()) != -1) {
                        builder.append((char) ch);

                    }
                    System.out.printf("zip fileName = %s\n\n####\n contents of file %s\n###\n", 
                    entryName, builder);
                } catch (Exception ex) {
                    ex.printStackTrace();//it is an example/proto :)
                }
            }

You can see the full example here: Sleepless in Pleasanton.