等价于Jar中的this.getClass（）。getClassLoader（）。getResource（“。”）。toURI（）

Question

I'm trying to achieve a way to obtain the base path of the current classloader when runnning from within a jar.

I mean programatically, I already know it should have the shape of "jarPath+jarFile.jar!/"

Unlike file system's call, getResource(".") or .getResource("/") do not work from inside the jar.

Ideally it should be an abstract solution for any file provider, so something like:

Path BASE_PATH = Paths.get(...getResource("").toURI())

which could return the correct root path for both jars and file system so I can use relative urls to my resources without having to do any conditional statements and url manual string parsing/build.

Answer 1

You should be able to find out the path of the jar and or target folder containing you class or any resource by using this code:

package com.stackoverflow.test;

import java.net.URL;
import java.nio.file.Paths;

public class ClassPathUtils {

  public static String getBasePath(String jarPath) {
    String path = getJarPathFromClass(jarPath);
    if (path == null) {
      return null;
    }

    if (path.startsWith("jar:")) {
      path = path.substring("jar:".length());
    }
    if (path.startsWith("file:")) {
      path = path.substring("file:".length());
    }
    if (path.endsWith(jarPath)) {
      path = path.substring(0, path.length()-jarPath.length());
    }

    return path;
  }
  public static String getBasePath(Class clazz) {
    return getBasePath(classNameDotClass(clazz));
  }
  private static String classNameDotClass(Class clazz) {
    return clazz.getName().replaceAll("\\.", "/") + ".class";
  }
  private static String getJarPathFromClass(String resource) {
    final URL url = ClassPathUtils.class.getClassLoader().getResource(resource);
    return url == null ? null : url.toString();
  }
  public static void main(String[] args) {
    //System.out.println(Paths.get(ClassPathUtils.getBasePath("."))); // doesn't work in a jar
    System.out.println(Paths.get(ClassPathUtils.getBasePath(ClassPathUtils.class)));

    System.out.println(Paths.get(ClassPathUtils.getBasePath("fonts/atcitadelscript.ttf"))); // any classpath resource

    System.out.println(Paths.get(ClassPathUtils.getBasePath(String.class))); // actually finds rt.jar

  }
}

If you run this code from your IDE, or from maven, it will give you the paths to target/classes for your own resources , or the path to a jar for other resources (Eg String.class). If you call it from a jar, it will always tell you the path of the jar file.

run from IDE:

/home/alexander/projects/stackoverflow/stuff/target/classes
/home/alexander/projects/stackoverflow/stuff/target/classes
/usr/lib/jvm/java-7-openjdk-amd64/jre/lib/rt.jar!`

run from JAR:

/home/alexander/projects/stackoverflow/stuff/target/test-stuff-0.1-SNAPSHOT.jar!
/home/alexander/projects/stackoverflow/stuff/target/test-stuff-0.1-SNAPSHOT.jar!
/usr/lib/jvm/java-7-openjdk-amd64/jre/lib/rt.jar!

Is that what you're looking for?