java.lang.ClassFormatError: Incompatible magic value 1885430635 in class file

野性酷女 2021-12-14 11:13 556阅读 0赞

以下是报错源码

public class MyClassLoader extends ClassLoader {
        
    
        private File classPathFile;
    
        public MyClassLoader() {
        
            String path = MyClassLoader.class.getResource("").getPath();
            this.classPathFile = new File(path);
        }
    
        @Override
        protected Class<?> findClass(String name) throws ClassNotFoundException {
        
            String className = MyClassLoader.class.getPackage().getName() + "." + name;
            if (classPathFile != null) {
        
    	        //这里出现错误，classloader只能加载.class文件
                File classFile = new File(classPathFile, name.replace(".", "\\") + ".java");
                if (classFile.exists()) {
        
                    try (FileInputStream in = new FileInputStream(classFile);
                         ByteArrayOutputStream out = new ByteArrayOutputStream()) {
        
                        byte[] bytes = new byte[1024];
                        int len;
                        while ((len = in.read(bytes)) != -1) {
        
                            out.write(bytes, 0, len);
                        }
                        return defineClass(className, out.toByteArray(), 0, out.size());
                    } catch (IOException e) {
        
                        e.printStackTrace();
                    }
                }
            }
            return super.findClass(name);
        }
    }

在使用自定义classloader加载类时，由于粗心大意，出现了一点错误.  
`java.lang.ClassFormatError: Incompatible magic value 1885430635 in class file xxx`  
原因是**不能使用ClassLoader加载java源码文件，就是.java文件，只能加载.class文件**  
因此上面需要修改  
`File classFile = new File(classPathFile, name.replace(".", "\\") + ".class");`

关于如何动态创建类并加载到内存中可参考[这里][Link 1]

[Link 1]: https://stackoverflow.com/questions/21544446/how-do-you-dynamically-compile-and-load-external-java-classes