java.lang.SecurityException: Prohibited package name: java.com.xx

Using the idea to create a new project, and then build a program called "java" folder, when you start inside the main function, appear as an exception:

According exception information, navigate to java.lang.ClassLoader.preDefineClass investigation, find the following code fragment:

/* Determine protection domain, and check that: 
        - not define java.* class, 
        - signer of this class matches signers for the rest of the classes in package. 
*/  
    private ProtectionDomain preDefineClass(String name,  
    ProtectionDomain protectionDomain)  
    {  
    if (!checkName(name))  
        throw new NoClassDefFoundError("IllegalName: " + name);  
    if ((name != null) && [color=red]name.startsWith("java.")[/color]) {  
        throw new SecurityException("Prohibited package name: " +  
            name.substring(0, name.lastIndexOf('.')));  
    }  
    if (protectionDomain == null) {  
        protectionDomain = getDefaultDomain();  
    }  
  
    if (name != null)  
        checkCerts(name, protectionDomain.getCodeSource());  
  
    return protectionDomain;  
    }  
  
......  
  
// true if the name is null or has the potential to be a valid binary name  
    private boolean checkName(String name) {  
    if ((name == null) || (name.length() == 0))  
        return true;  
    if ((name.indexOf('/') != -1)  
        || (!VM.allowArraySyntax() && (name.charAt(0) == '[')))  
        return false;  
    return true;  
    }  

Firstly, it can be seen preDefineClass class names were checked and found to java as a package name, then throw a security exception: Do not use the package name!

This security exception is a Java class loading "parent delegation model" (see here ) caused. In the parent delegation model, by the parent class loader to load a class, the lower loader is not loaded. In this embodiment the top of the loader loads the java BootstrapClassLoader defined under the classpath. * Classes in the package, and the package can not be loaded java.research by the lower loader AppClassLoader BootstrapClassLoader. It is also protective measures java security mechanism for malicious code taken.