从jar加载类时截断的类文件异常

Question

I am trying to read class, stored in my jar file.

When I do like this

private void registerClasses(Path jar, List<String> classNames) throws IOException {
    JarFile jarFile = new JarFile(jar.toFile());
    Enumeration<JarEntry> e = jarFile.entries();
    while (e.hasMoreElements()) {
        JarEntry je = e.nextElement();
        if (je.isDirectory() || !je.getName().endsWith(".class")) {
            continue;
        }

        String className = je.getName().substring(0, je.getName().length() - 6).replace('/', '.');
        if (classNames.contains(className)) {
            LOGGER.info("Found class in jar [{}].", className);
            InputStream stream = new JarInputStream(jarFile.getInputStream(je));
            byte[] classBytes = IOUtils.toByteArray(stream); // empty array
            Class<?> clz = this.defineClass(className, classBytes, 0, classBytes.length);
            LOGGER.info("Defined class: [{}].", clz.getClass());
        }
    }
}

I get java.lang.ClassFormatError: Truncated class file and byteArray appears to be empty.

What is the problem?

Answer 1

I remember running into that problem in the past and remembered the solution for that. I create input stream like this.

InputStream stream = new JarInputStream(jarFile.getInputStream(je));

But there is no need to create new JarInputStream as getInputStream already returns InputStream . So I changed to this

InputStream stream = jarFile.getInputStream(je);

And it started to work.