Reference:Java.lang.ClassLoader

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java.lang
public abstract class java.lang.ClassLoader

java.lang.Object
java.lang.ClassLoader


A ClassLoader is used for loading classes.

[edit] VM Implementors Note

This class must be implemented by the VM. The documented methods and natives must be implemented to support other provided class implementations in this package.
[edit] Known Direct Subclasses
SecureClassLoader
[edit] Known Indirect Subclasses

URLClassLoader

See Also

[edit] Summary

[edit] Protected Constructors

          ClassLoader ()
Constructs a new instance of this class with the system class loader as its parent.
          ClassLoader (ClassLoader parentLoader)
Constructs a new instance of this class with the given class loader as its parent.

[edit] Public Methods

        void  clearAssertionStatus ()
Clears the default, package and class assertion status of a classloader
    final    ClassLoader   getParent ()
Returns the specified ClassLoader's parent.
        URL   getResource (String resName)
Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.
        InputStream   getResourceAsStream (String resName)
Answers a stream on a resource found by looking up resName using the class loader's resource lookup algorithm.
        Enumeration   getResources (String resName)
Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.
      static  ClassLoader   getSystemClassLoader ()
Returns the system class loader.
      static  URL   getSystemResource (String resName)
Answers an URL specifying a resource which can be found by looking up resName using the system class loader's resource lookup algorithm.
      static  InputStream   getSystemResourceAsStream (String resName)
Answers a stream on a resource found by looking up resName using the system class loader's resource lookup algorithm.
      static  Enumeration   getSystemResources (String resName)
Answers an Enumeration of URLs containing all resources which can be found by looking up resName using the system class loader's resource lookup algorithm.
        Class   loadClass (String className)
Invoked by the Virtual Machine when resolving class references.
        void  setClassAssertionStatus (String cname, boolean enable)
Sets the assertion status of a class.
        void  setDefaultAssertionStatus (boolean enable)
Sets the default assertion status of a classloader
        void  setPackageAssertionStatus (String pname, boolean enable)
Sets the assertion status of a package.

[edit] Protected Methods

    final    Class   defineClass (byte[] classRep, int offset, int length)
This method is deprecated. Use defineClass(String, byte[], int, int)
    final    Class   defineClass (String name, ByteBuffer b, ProtectionDomain protectionDomain)

Defines a new class for the name, bytecodes in the byte buffer and the protection domain.

    final    Class   defineClass (String className, byte[] classRep, int offset, int length, ProtectionDomain protectionDomain)
Constructs a new class from an array of bytes containing a class definition in class file format and assigns the new class to the specified protection domain.
    final    Class   defineClass (String className, byte[] classRep, int offset, int length)
Constructs a new class from an array of bytes containing a class definition in class file format.
        Package   definePackage (String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase)
Define a new Package using the specified information.
        Class   findClass (String className)
Overridden by subclasses, by default throws ClassNotFoundException.
        String   findLibrary (String libName)
Answers the absolute path of the file containing the library associated with the given name, or null.
    final    Class   findLoadedClass (String className)
Attempts to find and return a class which has already been loaded by the virtual machine.
        URL   findResource (String resName)
Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.
        Enumeration   findResources (String resName)
Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.
    final    Class   findSystemClass (String className)
Attempts to load a class using the system class loader.
        Package   getPackage (String name)
Attempt to locate the requested package.
        Package[ ]  getPackages ()
Return all the packages known to this class loader.
        Class   loadClass (String className, boolean resolve)
Loads the class with the specified name, optionally linking the class after load.
    final    void  )">resolveClass (Class clazz)
Forces a class to be linked (initialized).
    final    void  , java.lang.Object[])">setSigners (Class c, Object[ ] signers)
Sets the signers of a class.

[edit] Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

[edit] Details

[edit] Protected Constructors

[edit] protected ClassLoader()

Constructs a new instance of this class with the system class loader as its parent.

Throws

SecurityException if a security manager exists and it does not allow the creation of new ClassLoaders.

[edit] protected ClassLoader(ClassLoader parentLoader)

Constructs a new instance of this class with the given class loader as its parent.

Parameters

parentLoader The ClassLoader to use as the new class loaders parent.

Throws

SecurityException if a security manager exists and it does not allow the creation of new ClassLoaders.
NullPointerException if the parent is null.

[edit] Public Methods

[edit] public void clearAssertionStatus()

Clears the default, package and class assertion status of a classloader

[edit] public final ClassLoader getParent()

Returns the specified ClassLoader's parent.

Returns

  • The class or null.

Throws

SecurityException if a security manager exists and it does not allow the parent loader to be retrieved.

[edit] public URL getResource(String resName)

Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm. The default behavior is just to return null.

Parameters

resName String the name of the resource to find.

Returns

  • The location of the resource.

See Also

[edit] public InputStream getResourceAsStream(String resName)

Answers a stream on a resource found by looking up resName using the class loader's resource lookup algorithm. The default behavior is just to return null.

Parameters

resName String the name of the resource to find.

Returns

  • A stream on the resource or null.

See Also

[edit] public Enumeration getResources(String resName)

Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm. The default behavior is just to return an empty Enumeration.

Parameters

resName String the name of the resource to find.

Returns

  • The location of the resources.

Throws

IOException

[edit] public static ClassLoader getSystemClassLoader()

Returns the system class loader. This is the parent for new ClassLoader instances, and is typically the class loader used to start the application. If a security manager is present, and the caller's class loader is not null and the caller's class loader is not the same as or an ancestor of the system class loader, then this method calls the security manager's checkPermission method with a RuntimePermission("getClassLoader") permission to ensure it's ok to access the system class loader. If not, a SecurityException will be thrown.

Returns

  • The system classLoader.

Throws

SecurityException if a security manager exists and it does not allow access to the system class loader.

[edit] public static URL getSystemResource(String resName)

Answers an URL specifying a resource which can be found by looking up resName using the system class loader's resource lookup algorithm.

Parameters

resName The name of the resource to find.

Returns

  • A URL specifying a system resource or null.

See Also

[edit] public static InputStream getSystemResourceAsStream(String resName)

Answers a stream on a resource found by looking up resName using the system class loader's resource lookup algorithm. Basically, the contents of the java.class.path are searched in order, looking for a path which matches the specified resource.

Parameters

resName The name of the resource to find.

Returns

  • A stream on the resource or null.

See Also

[edit] public static Enumeration getSystemResources(String resName)

Answers an Enumeration of URLs containing all resources which can be found by looking up resName using the system class loader's resource lookup algorithm.

Parameters

resName String the name of the resource to find.

Returns

  • An Enumeration of URLs containing the system resources

Throws

IOException

[edit] public Class loadClass(String className)

Invoked by the Virtual Machine when resolving class references. Equivalent to loadClass(className, false);

Parameters

className The name of the class to search for.

Returns

  • The Class object.

Throws

ClassNotFoundException if the class could not be found.

[edit] public void setClassAssertionStatus(String cname, boolean enable)

Sets the assertion status of a class.

Parameters

cname Class name
enable Enable or disable assertion

[edit] public void setDefaultAssertionStatus(boolean enable)

Sets the default assertion status of a classloader

Parameters

enable Enable or disable assertion

[edit] public void setPackageAssertionStatus(String pname, boolean enable)

Sets the assertion status of a package.

Parameters

pname Package name
enable Enable or disable assertion

[edit] Protected Methods

[edit] protected final Class defineClass(byte[] classRep, int offset, int length)

This method is deprecated. Use defineClass(String, byte[], int, int)Constructs a new class from an array of bytes containing a class definition in class file format.

Parameters

classRep A memory image of a class file.
offset The offset into the classRep.
length The length of the class file.

Throws

ClassFormatError

[edit] protected final Class defineClass(String name, ByteBuffer b, ProtectionDomain protectionDomain)

Defines a new class for the name, bytecodes in the byte buffer and the protection domain.

Parameters

name The name of the class to define.
b The byte buffer containing the bytecodes of the new class.
protectionDomain The protection domain this class belongs to.

Returns

  • The defined class.

Throws

ClassFormatError if an invalid class file is defined.

[edit] protected final Class defineClass(String className, byte[] classRep, int offset, int length, ProtectionDomain protectionDomain)

Constructs a new class from an array of bytes containing a class definition in class file format and assigns the new class to the specified protection domain.

Parameters

className The name of the new class.
classRep A memory image of a class file.
offset The offset into the classRep.
length The length of the class file.
protectionDomain The protection domain this class should belongs to.

Throws

ClassFormatError

[edit] protected final Class defineClass(String className, byte[] classRep, int offset, int length)

Constructs a new class from an array of bytes containing a class definition in class file format.

Parameters

className The name of the new class
classRep A memory image of a class file
offset The offset into the classRep
length The length of the class file

Throws

ClassFormatError

[edit] protected Package definePackage(String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase)

Define a new Package using the specified information.

Parameters

name The name of the package
specTitle The title of the specification for the Package
specVersion The version of the specification for the Package
specVendor The vendor of the specification for the Package
implTitle The implementation title of the Package
implVersion The implementation version of the Package
implVendor The specification vendor of the Package
sealBase If sealBase is null, the package is left unsealed. Otherwise, the the package is sealed using this URL.

Returns

  • The Package created

Throws

IllegalArgumentException if the Package already exists

[edit] protected Class findClass(String className)

Overridden by subclasses, by default throws ClassNotFoundException. This method is called by loadClass() after the parent ClassLoader has failed to find a loaded class of the same name.

Parameters

className The name of the class to search for.

Returns

  • The class or null.

Throws

ClassNotFoundException if the class cannot be found.

[edit] protected String findLibrary(String libName)

Answers the absolute path of the file containing the library associated with the given name, or null. If null is answered, the system searches the directories specified by the system property "java.library.path".

Parameters

libName The name of the library to find.

Returns

  • The library file name or null.

[edit] protected final Class findLoadedClass(String className)

Attempts to find and return a class which has already been loaded by the virtual machine. Note that the class may not have been linked and the caller should call resolveClass() on the result if necessary.

Parameters

className The name of the class to search for.

Returns

  • The class or null.

[edit] protected URL findResource(String resName)

Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm. The default behavior is just to return null. This should be implemented by a ClassLoader.

Parameters

resName The name of the resource to find.

Returns

  • The location of the resource.

[edit] protected Enumeration findResources(String resName)

Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm. The default behavior is just to return an empty Enumeration.

Parameters

resName The name of the resource to find.

Returns

  • The locations of the resources.

Throws

IOException when an error occurs

[edit] protected final Class findSystemClass(String className)

Attempts to load a class using the system class loader. Note that the class has already been been linked.

Parameters

className The name of the class to search for.

Returns

  • The class which was loaded.

Throws

ClassNotFoundException if the class cannot be found.

[edit] protected Package getPackage(String name)

Attempt to locate the requested package. If no package information can be located, null is returned.

Parameters

name The name of the package to find

Returns

  • The package requested, or null

[edit] protected Package[ ]getPackages()

Return all the packages known to this class loader.

Returns

  • All the packages known to this classloader

[edit] protected Class loadClass(String className, boolean resolve)

Loads the class with the specified name, optionally linking the class after load. Steps are: 1) Call findLoadedClass(className) to determine if class is loaded 2) Call loadClass(className, resolveClass) on the parent loader. 3) Call findClass(className) to find the class

Parameters

className The name of the class to search for.
resolve Indicates if class should be resolved after loading.

Returns

  • The Class object.

Throws

ClassNotFoundException if the class could not be found.

[edit] protected final void resolveClass(Class clazz)

Forces a class to be linked (initialized). If the class has already been linked this operation has no effect.

Parameters

clazz The Class to link.

Throws

NullPointerException if clazz is null.

See Also

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

Sets the signers of a class.

Parameters

c The Class object
signers The signers for the class

[edit] References

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