ResourceUtils.java

package sample;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.regex.Pattern;

public class ResourceUtils {
    private static String path(String path) {
        return path.replace('\\', '/'); // convert to UNIX path
    }

    public static List<String> findResources(String pattern) {
        return findResources(Pattern.compile(pattern));
    }

    public static List<String> findResources(Pattern pattern) {
        List<String> list = new ArrayList<String>();
        Enumeration<URL> urls = null;
        try {
            urls = ResourceUtils.class.getClassLoader().getResources("");
        } catch (IOException e) {
            return list;
        }

        while (urls.hasMoreElements()) {
            findResourcesRecursive(list, urls.nextElement().getPath(), pattern);
        }
        return list;
    }

    private static void findResourcesRecursive(List<String> list, String path, Pattern pattern) {
        File file = new File(path);
        if (file.isDirectory()) {
            for (File file2: file.listFiles()) {
                findResourcesRecursive(list, file2.getPath(), pattern);
            }
        }
        else {
            if (pattern.matcher(file.getName()).find()) {
                list.add(ResourceUtils.path(path));
            }
        }
    }

    public static String getResourcePath(String path) {
        URL url = ResourceUtils.class.getClass().getResource(path);
        return ResourceUtils.path(url.getPath());
    }
}

ResourceUtilsTest.java

package sample;

import org.junit.Test;

import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.List;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.CoreMatchers.nullValue;
import static org.junit.Assert.*;

public class ResourceUtilsTest {
    @Test
    public void testGetResources() throws Exception {
        Enumeration<URL> urls;

        urls = this.getClass().getClassLoader().getResources("");
        assertThat(urls.hasMoreElements(), is(true));
        assertThat(urls.nextElement().toString(), is("file:/C:/workspace/poi/build/classes/test/"));
        assertThat(urls.nextElement().toString(), is("file:/C:/workspace/poi/build/classes/main/"));
        assertThat(urls.nextElement().toString(), is("file:/C:/workspace/poi/build/resources/test/"));
        assertThat(urls.nextElement().toString(), is("file:/C:/workspace/poi/build/resources/main/"));
        assertThat(urls.hasMoreElements(), is(false));

        urls = this.getClass().getClassLoader().getResources("foobar");

        assertThat(urls.hasMoreElements(), is(false));

        urls = this.getClass().getClassLoader().getResources("sample.xlsx");

        assertThat(urls.hasMoreElements(), is(true));
    }

    @Test
    public void testClassGetResources() throws Exception {
        URL url;
        url = this.getClass().getResource("/");
        assertThat(url.toString(), is("file:/C:/workspace/poi/build/classes/test/"));

        url = this.getClass().getResource("sample.xlsx");

        assertThat(url, is(nullValue()));

        url = this.getClass().getResource("/sample.xlsx");
        assertThat(url.toString(), is("file:/C:/workspace/poi/build/resources/test/sample.xlsx"));
    }

    @Test
    public void testClassLoaderGetResources() throws Exception {
        URL url;
        url = this.getClass().getClassLoader().getResource("/");
        assertThat(url, is(nullValue()));

        url = this.getClass().getClassLoader().getResource("sample.xlsx");

        assertThat(url.toString(), is("file:/C:/workspace/poi/build/resources/test/sample.xlsx"));

        url = this.getClass().getResource("/sample.xlsx");
        assertThat(url.toString(), is("file:/C:/workspace/poi/build/resources/test/sample.xlsx"));
    }

    @Test
    public void testFindResources() throws Exception {
        List<String> list = ResourceUtils.findResources("sample.*\\.xlsx");
        assertThat(list.size(), is(3));
        assertThat(list.get(0), is("C:/workspace/poi/build/resources/test/sample.xlsx"));
        assertThat(list.get(1), is("C:/workspace/poi/build/resources/test/sampleRow.xlsx"));
        assertThat(list.get(2), is("C:/workspace/poi/build/resources/main/sample2.xlsx"));
    }
}