ResourceTest.java

package hollywood.framework;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.util.FileCopyUtils;
import org.springframework.util.SystemPropertyUtils;

import java.io.InputStreamReader;

import static java.lang.System.out;

@SpringBootTest
class ResourceTest {

    @Test
    void resources(@Autowired ResourceLoader resourceLoader, @Autowired ResourcePatternResolver resourcePatternResolver) throws Exception {
        log(resourceLoader.getResource(SystemPropertyUtils.resolvePlaceholders("file://${HOME}/Desktop/test.txt")));
        log(resourceLoader.getResource("classpath:/my/test.txt"));
        log(resourceLoader.getResource("https://start.spring.io"));
        var resources = resourcePatternResolver.getResources(
                ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + "application.properties");
        for (var r : resources)
            out.println(r.getURI());
        Assertions.assertTrue(resources.length > 0, "there should be at least one file of this name");
    }

    private static String truncate(String text) {
        var max = 20;
        return (text.length() > max) ? text.substring(0, max) + "..." : text;
    }

    private static void log(Resource resource) {

        try (var in = new InputStreamReader(resource.getInputStream())) {
            Assertions.assertTrue(resource.exists(), "the resource with the url [" + resource.getURI() + "] must exist");
            var string = FileCopyUtils.copyToString(in).trim();
            out.println("read: [" + truncate(string) + "] from [" + resource.getURI() + "]");
        }//
        catch (Throwable t) {
            out.println("got an error! " + t.getMessage());  // don't care ..
        }
    }
}