Reading a resource file from within jar

Rather than trying to address the resource as a File just ask the ClassLoader to return an InputStream for the resource instead via getResourceAsStream:

try (InputStream in = getClass().getResourceAsStream("/file.txt");
    BufferedReader reader = new BufferedReader(new InputStreamReader(in))) {
    // Use resource
}

As long as the file.txt resource is available on the classpath then this approach will work the same way regardless of whether the file.txt resource is in a classes/ directory or inside a jar.

The URI is not hierarchical occurs because the URI for a resource within a jar file is going to look something like this: file:/example.jar!/file.txt. You cannot read the entries within a jar (a zip file) like it was a plain old File.

This is explained well by the answers to:

• How do I read a resource file from a Java jar file?
• Java Jar file: use resource errors: URI is not hierarchical

In my case I finally made it with

import java.lang.Thread;
import java.io.BufferedReader;
import java.io.InputStreamReader;

final BufferedReader in = new BufferedReader(new InputStreamReader(
      Thread.currentThread().getContextClassLoader().getResourceAsStream("file.txt"))
); // no initial slash in file.txt

The problem is that certain third party libraries require file pathnames rather than input streams. Most of the answers don't address this issue.

In this case, one workaround is to copy the resource contents into a temporary file. The following example uses jUnit's TemporaryFolder.

    private List<String> decomposePath(String path){
        List<String> reversed = Lists.newArrayList();
        File currFile = new File(path);
        while(currFile != null){
            reversed.add(currFile.getName());
            currFile = currFile.getParentFile();
        }
        return Lists.reverse(reversed);
    }

    private String writeResourceToFile(String resourceName) throws IOException {
        ClassLoader loader = getClass().getClassLoader();
        InputStream configStream = loader.getResourceAsStream(resourceName);
        List<String> pathComponents = decomposePath(resourceName);
        folder.newFolder(pathComponents.subList(0, pathComponents.size() - 1).toArray(new String[0]));
        File tmpFile = folder.newFile(resourceName);
        Files.copy(configStream, tmpFile.toPath(), REPLACE_EXISTING);
        return tmpFile.getAbsolutePath();
    }

I have found a fix

BufferedReader br = new BufferedReader(new InputStreamReader(Main.class.getResourceAsStream(path)));

Replace "Main" with the java class you coded it in. replace "path" with the path within the jar file.

for example, if you put State1.txt in the package com.issac.state, then type the path as "/com/issac/state/State1" if you run Linux or Mac. If you run Windows then type the path as "\com\issac\state\State1". Don't add the .txt extension to the file unless the File not found exception occurs.

This code works both in Eclipse and in Exported Runnable JAR

private String writeResourceToFile(String resourceName) throws IOException {
    File outFile = new File(certPath + File.separator + resourceName);

    if (outFile.isFile())
        return outFile.getAbsolutePath();
    
    InputStream resourceStream = null;
    
    // Java: In caso di JAR dentro il JAR applicativo 
    URLClassLoader urlClassLoader = (URLClassLoader)Cypher.class.getClassLoader();
    URL url = urlClassLoader.findResource(resourceName);
    if (url != null) {
        URLConnection conn = url.openConnection();
        if (conn != null) {
            resourceStream = conn.getInputStream();
        }
    }
    
    if (resourceStream != null) {
        Files.copy(resourceStream, outFile.toPath(), StandardCopyOption.REPLACE_EXISTING);
        return outFile.getAbsolutePath();
    } else {
        System.out.println("Embedded Resource " + resourceName + " not found.");
    }
    
    return "";
}   

finally i solved errors:

String input_path = "resources\\file.txt";
        
        input_path = input_path.replace("\\", "/");  // doesn't work with back slash
        
        URL file_url = getClass().getClassLoader().getResource(input_path);
        String file_path = new URI(file_url.toString().replace(" ","%20")).getSchemeSpecificPart();
        InputStream file_inputStream = file_url.openStream();

You can use class loader which will read from classpath as ROOT path (without "/" in the beginning)

InputStream in = getClass().getClassLoader().getResourceAsStream("file.txt"); 
BufferedReader reader = new BufferedReader(new InputStreamReader(in));

For some reason classLoader.getResource() always returned null when I deployed the web application to WildFly 14. getting classLoader from getClass().getClassLoader() or Thread.currentThread().getContextClassLoader() returns null.

getClass().getClassLoader() API doc says,

"Returns the class loader for the class. Some implementations may use null to represent the bootstrap class loader. This method will return null in such implementations if this class was loaded by the bootstrap class loader."

may be if you are using WildFly and yours web application try this

request.getServletContext().getResource() returned the resource url. Here request is an object of ServletRequest.

Below code works with Spring boot(kotlin):

val authReader = InputStreamReader(javaClass.getResourceAsStream("/file1.json"))