Class ClassLoader

protected ClassLoader()
            throws SecurityException

Create a new ClassLoader with as parent the system classloader. There may be a security check for checkCreateClassLoader.

Throws:

SecurityException - if the security check fails

protected ClassLoader(ClassLoader parent)

Create a new ClassLoader with the specified parent. The parent will be consulted when a class or resource is requested through loadClass() or getResource(). Only when the parent classloader cannot provide the requested class or resource the findClass() or findResource() method of this classloader will be called. There may be a security check for checkCreateClassLoader.

Parameters:

parent - the classloader's parent, or null for the bootstrap classloader

Throws:

SecurityException - if the security check fails

Since:

1.2

public void clearAssertionStatus()

Resets the default assertion status of this classloader, its packages and classes, all to false. This allows overriding defaults inherited from the command line.

Since:

1.4

See Also:

setDefaultAssertionStatus(boolean), setClassAssertionStatus(String,boolean), setPackageAssertionStatus(String,boolean)

protected final Class defineClass(byte[] data,
                                     int offset,
                                     int len)
            throws ClassFormatError

Deprecated. use defineClass(String,byte[],int,int) instead

Helper to define a class using a string of bytes. This version is not secure.

Parameters:

data - the data representing the classfile, in classfile format

offset - the offset into the data where the classfile starts

len - the length of the classfile data in the array

Returns:

the class that was defined

Throws:

ClassFormatError - if data is not in proper classfile format

IndexOutOfBoundsException - if offset or len is negative, or offset + len exceeds data

protected final Class defineClass(String name,
                                     byte[] data,
                                     int offset,
                                     int len)
            throws ClassFormatError

Helper to define a class using a string of bytes without a ProtectionDomain. Subclasses should call this method from their findClass() implementation. The name should use '.' separators, and discard the trailing ".class". The default protection domain has the permissions of Policy.getPolicy().getPermissions(new CodeSource(null, null)).

Parameters:

name - the name to give the class, or null if unknown

data - the data representing the classfile, in classfile format

offset - the offset into the data where the classfile starts

len - the length of the classfile data in the array

Returns:

the class that was defined

Throws:

ClassFormatError - if data is not in proper classfile format

IndexOutOfBoundsException - if offset or len is negative, or offset + len exceeds data

SecurityException - if name starts with "java."

Since:

1.1

protected final Class defineClass(String name,
                                     byte[] data,
                                     int offset,
                                     int len,
                                     ProtectionDomain domain)
            throws ClassFormatError

Helper to define a class using a string of bytes. Subclasses should call this method from their findClass() implementation. If the domain is null, the default of Policy.getPolicy().getPermissions(new CodeSource(null, null)) is used. Once a class has been defined in a package, all further classes in that package must have the same set of certificates or a SecurityException is thrown.

Parameters:

name - the name to give the class. null if unknown

data - the data representing the classfile, in classfile format

offset - the offset into the data where the classfile starts

len - the length of the classfile data in the array

domain - the ProtectionDomain to give to the class, null for the default protection domain

Returns:

the class that was defined

Throws:

ClassFormatError - if data is not in proper classfile format

IndexOutOfBoundsException - if offset or len is negative, or offset + len exceeds data

SecurityException - if name starts with "java.", or if certificates do not match up

Since:

1.2

protected final Class defineClass(String name,
                                     ByteBuffer buf,
                                     ProtectionDomain domain)
            throws ClassFormatError

Helper to define a class using the contents of a byte buffer. If the domain is null, the default of Policy.getPolicy().getPermissions(new CodeSource(null, null)) is used. Once a class has been defined in a package, all further classes in that package must have the same set of certificates or a SecurityException is thrown.

Parameters:

name - the name to give the class. null if unknown

buf - a byte buffer containing bytes that form a class.

domain - the ProtectionDomain to give to the class, null for the default protection domain

Returns:

the class that was defined

Throws:

ClassFormatError - if data is not in proper classfile format

SecurityException - if name starts with "java.", or if certificates do not match up

Since:

1.5

protected Package definePackage(String name,
                                String specTitle,
                                String specVendor,
                                String specVersion,
                                String implTitle,
                                String implVendor,
                                String implVersion,
                                URL sealed)

Defines a new package and creates a Package object. The package should be defined before any class in the package is defined with defineClass(). The package should not yet be defined before in this classloader or in one of its parents (which means that getPackage() should return null). All parameters except the name of the package may be null.

Subclasses should call this method from their findClass() implementation before calling defineClass() on a Class in a not yet defined Package (which can be checked by calling getPackage()).

Parameters:

name - the name of the Package

specTitle - the name of the specification

specVendor - the name of the specification designer

specVersion - the version of this specification

implTitle - the name of the implementation

implVendor - the vendor that wrote this implementation

implVersion - the version of this implementation

sealed - if sealed the origin of the package classes

Returns:

the Package object for the specified package

Throws:

IllegalArgumentException - if the package name is null or it was already defined by this classloader or one of its parents

Since:

1.2

See Also:

Package

protected Class findClass(String name)
            throws ClassNotFoundException

Called for every class name that is needed but has not yet been defined by this classloader or one of its parents. It is called by loadClass() after both findLoadedClass() and parent.loadClass() couldn't provide the requested class.

The default implementation throws a ClassNotFoundException. Subclasses should override this method. An implementation of this method in a subclass should get the class bytes of the class (if it can find them), if the package of the requested class doesn't exist it should define the package and finally it should call define the actual class. It does not have to resolve the class. It should look something like the following:

 // Get the bytes that describe the requested class
 byte[] classBytes = classLoaderSpecificWayToFindClassBytes(name);
 // Get the package name
 int lastDot = name.lastIndexOf('.');
 if (lastDot != -1)
   {
     String packageName = name.substring(0, lastDot);
     // Look if the package already exists
     if (getPackage(packageName) == null)
       {
         // define the package
         definePackage(packageName, ...);
       }
   }
 // Define and return the class
  return defineClass(name, classBytes, 0, classBytes.length);
 

loadClass() makes sure that the Class returned by findClass() will later be returned by findLoadedClass() when the same class name is requested.

Parameters:

name - class name to find (including the package name)

Returns:

the requested Class

Throws:

ClassNotFoundException - when the class can not be found

Since:

1.2

protected String findLibrary(String name)

Called by Runtime.loadLibrary() to get an absolute path to a (system specific) library that was requested by a class loaded by this classloader. The default implementation returns null. It should be implemented by subclasses when they have a way to find the absolute path to a library. If this method returns null the library is searched for in the default locations (the directories listed in the java.library.path system property).

Parameters:

name - the (system specific) name of the requested library

Returns:

the full pathname to the requested library, or null

Since:

1.2

See Also:

Runtime.loadLibrary(String)

protected final Class findLoadedClass(String name)

Helper to find an already-loaded class in this ClassLoader.

Parameters:

name - the name of the class to find

Returns:

the found Class, or null if it is not found

Since:

1.1

protected URL findResource(String name)

Called whenever a resource is needed that could not be provided by one of the parents of this classloader. It is called by getResource() after parent.getResource() couldn't provide the requested resource.

The default implementation always returns null. Subclasses should override this method when they can provide a way to return a URL to a named resource.

Parameters:

name - the name of the resource to be found

Returns:

a URL to the named resource or null when not found

Since:

1.2

protected Enumeration findResources(String name)
            throws IOException

Called whenever all locations of a named resource are needed. It is called by getResources() after it has called parent.getResources(). The results are combined by the getResources() method.

The default implementation always returns an empty Enumeration. Subclasses should override it when they can provide an Enumeration of URLs (possibly just one element) to the named resource. The first URL of the Enumeration should be the same as the one returned by findResource.

Parameters:

name - the name of the resource to be found

Returns:

a possibly empty Enumeration of URLs to the named resource

Throws:

IOException - if I/O errors occur in the process

Since:

1.2

protected final Class findSystemClass(String name)
            throws ClassNotFoundException

Helper to find a Class using the system classloader, possibly loading it. A subclass usually does not need to call this, if it correctly overrides findClass(String).

Parameters:

name - the name of the class to find

Returns:

the found class

Throws:

ClassNotFoundException - if the class cannot be found

protected Package getPackage(String name)

Returns the Package object for the requested package name. It returns null when the package is not defined by this classloader or one of its parents.

Parameters:

name - the package name to find

Returns:

the package, if defined

Since:

1.2

protected Package[] getPackages()

Returns all Package objects defined by this classloader and its parents.

Returns:

an array of all defined packages

Since:

1.2

public final ClassLoader getParent()

Returns the parent of this classloader. If the parent of this classloader is the bootstrap classloader then this method returns null. A security check may be performed on RuntimePermission("getClassLoader").

Returns:

the parent ClassLoader

Throws:

SecurityException - if the security check fails

Since:

1.2

public URL getResource(String name)

Get the URL to a resource using this classloader or one of its parents. First tries to get the resource by calling getResource() on the parent classloader. If the parent classloader returns null then it tries finding the resource by calling findResource() on this classloader. The resource name should be separated by '/' for path elements.

Subclasses should not override this method but should override findResource() which is called by this method.

Parameters:

name - the name of the resource relative to this classloader

Returns:

the URL to the resource or null when not found

public InputStream getResourceAsStream(String name)

Get a resource as stream using this classloader or one of its parents. First calls getResource() and if that returns a URL to the resource then it calls and returns the InputStream given by URL.openStream().

Subclasses should not override this method but should override findResource() which is called by this method.

Parameters:

name - the name of the resource relative to this classloader

Returns:

an InputStream to the resource, or null

Since:

1.1

public Enumeration getResources(String name)
            throws IOException

Returns an Enumeration of all resources with a given name that can be found by this classloader and its parents. Certain classloaders (such as the URLClassLoader when given multiple jar files) can have multiple resources with the same name that come from multiple locations. It can also occur that a parent classloader offers a resource with a certain name and the child classloader also offers a resource with that same name. getResource() only offers the first resource (of the parent) with a given name. This method lists all resources with the same name. The name should use '/' as path separators.

The Enumeration is created by first calling getResources() on the parent classloader and then calling findResources() on this classloader.

Parameters:

name - the resource name

Returns:

an enumaration of all resources found

Throws:

IOException - if I/O errors occur in the process

Since:

1.2

public static ClassLoader getSystemClassLoader()

Returns the system classloader. The system classloader (also called the application classloader) is the classloader that is used to load the application classes on the classpath (given by the system property java.class.path. This is set as the context class loader for a thread. The system property java.system.class.loader, if defined, is taken to be the name of the class to use as the system class loader, which must have a public constructor which takes a ClassLoader as a parent. The parent class loader passed in the constructor is the default system class loader.

Note that this is different from the bootstrap classloader that actually loads all the real "system" classes (the bootstrap classloader is the parent of the returned system classloader).

A security check will be performed for RuntimePermission("getClassLoader") if the calling class is not a parent of the system class loader.

Returns:

the system class loader

Throws:

SecurityException - if the security check fails

IllegalStateException - if this is called recursively

Since:

1.2

public static final URL getSystemResource(String name)

Get the URL to a resource using the system classloader.

Parameters:

name - the name of the resource relative to the system classloader

Returns:

the URL to the resource

Since:

1.1

public static final InputStream getSystemResourceAsStream(String name)

Get a resource using the system classloader.

Parameters:

name - the name of the resource relative to the system classloader

Returns:

an input stream for the resource, or null

Since:

1.1

public static Enumeration getSystemResources(String name)
            throws IOException

Get an Enumeration of URLs to resources with a given name using the the system classloader. The enumeration firsts lists the resources with the given name that can be found by the bootstrap classloader followed by the resources with the given name that can be found on the classpath.

Parameters:

name - the name of the resource relative to the system classloader

Returns:

an Enumeration of URLs to the resources

Throws:

IOException - if I/O errors occur in the process

Since:

1.2

public Class loadClass(String name)
            throws ClassNotFoundException

Load a class using this ClassLoader or its parent, without resolving it. Calls loadClass(name, false).

Subclasses should not override this method but should override findClass() which is called by this method.

Parameters:

name - the name of the class relative to this ClassLoader

Returns:

the loaded class

Throws:

ClassNotFoundException - if the class cannot be found

protected Class loadClass(String name,
                             boolean resolve)
            throws ClassNotFoundException

Load a class using this ClassLoader or its parent, possibly resolving it as well using resolveClass(). It first tries to find out if the class has already been loaded through this classloader by calling findLoadedClass(). Then it calls loadClass() on the parent classloader (or when there is no parent it uses the VM bootclassloader). If the class is still not loaded it tries to create a new class by calling findClass(). Finally when resolve is true it also calls resolveClass() on the newly loaded class.

Subclasses should not override this method but should override findClass() which is called by this method.

Parameters:

name - the fully qualified name of the class to load

resolve - whether or not to resolve the class

Returns:

the loaded class

Throws:

ClassNotFoundException - if the class cannot be found

protected final void resolveClass(Class c)

Links the class, if that has not already been done. Linking basically resolves all references to other classes made by this class.

Parameters:

c - the class to resolve

Throws:

NullPointerException - if c is null

public void setClassAssertionStatus(String name,
                                    boolean enabled)

Set the default assertion status for a class. This only affects the status of top-level classes, any other string is harmless.

Parameters:

name - the class to affect

enabled - true to set the default to enabled

Throws:

NullPointerException - if name is null

Since:

1.4

See Also:

setDefaultAssertionStatus(boolean), setPackageAssertionStatus(String,boolean), clearAssertionStatus()

public void setDefaultAssertionStatus(boolean enabled)

Set the default assertion status for classes loaded by this classloader, used unless overridden by a package or class request.

Parameters:

enabled - true to set the default to enabled

Since:

1.4

See Also:

setClassAssertionStatus(String,boolean), setPackageAssertionStatus(String,boolean), clearAssertionStatus()

public void setPackageAssertionStatus(String name,
                                      boolean enabled)

Set the default assertion status for packages, used unless overridden by a class request. This default also covers subpackages, unless they are also specified. The unnamed package should use null for the name.

Parameters:

name - the package (and subpackages) to affect

enabled - true to set the default to enabled

Since:

1.4

See Also:

setDefaultAssertionStatus(boolean), setClassAssertionStatus(String,boolean), clearAssertionStatus()

protected final void setSigners(Class c,
                                Object[] signers)

Helper to set the signers of a class. This should be called after defining the class.

Parameters:

c - the Class to set signers of

signers - the signers to set

Since:

1.1