ClassLoader
abstract class ClassLoader
kotlin.Any | |
↳ | java.lang.ClassLoader |
A class loader is an object that is responsible for loading classes. The class ClassLoader
is an abstract class. Given the binary name of a class, a class loader should attempt to locate or generate data that constitutes a definition for the class. A typical strategy is to transform the name into a file name and then read a "class file" of that name from a file system.
Every Class
object contains a reference
to the ClassLoader
that defined it.
Class
objects for array classes are not created by class loaders, but are created automatically as required by the Java runtime. The class loader for an array class, as returned by java.lang.Class#getClassLoader()
is the same as the class loader for its element type; if the element type is a primitive type, then the array class has no class loader.
Applications implement subclasses of ClassLoader
in order to extend the manner in which the Java virtual machine dynamically loads classes.
Class loaders may typically be used by security managers to indicate security domains.
In addition to loading classes, a class loader is also responsible for locating resources. A resource is some data (a ".class
" file, configuration data, or an image for example) that is identified with an abstract '/'-separated path name. Resources are typically packaged with an application or library so that they can be located by code in the application or library. In some cases, the resources are included so that they can be located by other libraries.
The ClassLoader
class uses a delegation model to search for classes and resources. Each instance of ClassLoader
has an associated parent class loader. When requested to find a class or resource, a ClassLoader
instance will usually delegate the search for the class or resource to its parent class loader before attempting to find the class or resource itself.
Class loaders that support concurrent loading of classes are known as isRegisteredAsParallelCapable() parallel capable
class loaders and are required to register themselves at their class initialization time by invoking the registerAsParallelCapable ClassLoader.registerAsParallelCapable
method. Note that the ClassLoader
class is registered as parallel capable by default. However, its subclasses still need to register themselves if they are parallel capable. In environments in which the delegation model is not strictly hierarchical, class loaders need to be parallel capable, otherwise class loading can lead to deadlocks because the loader lock is held for the duration of the class loading process (see #loadClass methods).
Run-time Built-in Class Loaders
The Java run-time has the following built-in class loaders:- Bootstrap class loader. It is the virtual machine's built-in class loader, typically represented as
null
, and does not have a parent. - System class loader. It is also known as application class loader and is distinct from the platform class loader. The system class loader is typically used to define classes on the application class path, module path, and JDK-specific tools. The platform class loader is the parent or an ancestor of the system class loader, so the system class loader can load platform classes by delegating to its parent.
Normally, the Java virtual machine loads classes from the local file system in a platform-dependent manner. However, some classes may not originate from a file; they may originate from other sources, such as the network, or they could be constructed by an application. The method defineClass
converts an array of bytes into an instance of class Class
. Instances of this newly defined class can be created using Class.newInstance
.
The methods and constructors of objects created by a class loader may reference other classes. To determine the class(es) referred to, the Java virtual machine invokes the #loadClass method of the class loader that originally created the class.
For example, an application could create a network class loader to download class files from a server. Sample code might look like:
ClassLoader loader = new NetworkClassLoader(host, port); Object main = loader.loadClass("Main", true).newInstance(); . . .
The network class loader subclass must define the methods findClass
and loadClassData
to load a class from the network. Once it has downloaded the bytes that make up the class, it should use the method #defineClass to create a class instance. A sample implementation is:
class NetworkClassLoader extends ClassLoader { String host; int port; public Class findClass(String name) { byte[] b = loadClassData(name); return defineClass(name, b, 0, b.length); } private byte[] loadClassData(String name) { // load the class data from the connection . . . } }
Binary names
Any class name provided as a String
parameter to methods in ClassLoader
must be a binary name as defined by The Java Language Specification.
Examples of valid class names include:
"java.lang.String" "javax.swing.JSpinner$DefaultEditor" "java.security.KeyStore$Builder$FileBuilder$1" "java.net.URLClassLoader$3$1"
Any package name provided as a String
parameter to methods in ClassLoader
must be either the empty string (denoting an unnamed package) or a fully qualified name as defined by The Java Language Specification.
Summary
Protected constructors | |
---|---|
ClassLoader(parent: ClassLoader!) Creates a new class loader using the specified parent class loader for delegation. |
|
Creates a new class loader using the |
Public methods | |
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open Unit |
Sets the default assertion status for this class loader to |
ClassLoader! |
Returns the parent class loader for delegation. |
open URL! |
getResource(name: String!) Finds the resource with the given name. |
open InputStream! |
getResourceAsStream(name: String!) Returns an input stream for reading the specified resource. |
open Enumeration<URL!>! |
getResources(name: String!) Finds all the resources with the given name. |
open static ClassLoader! |
Returns the system class loader. |
open static URL! |
getSystemResource(name: String!) Find a resource of the specified name from the search path used to load classes. |
open static InputStream! |
getSystemResourceAsStream(name: String!) Open for reading, a resource of the specified name from the search path used to load classes. |
open static Enumeration<URL!>! |
getSystemResources(name: String!) Finds all resources of the specified name from the search path used to load classes. |
open Class<*>! |
Loads the class with the specified binary name. |
open Unit |
setClassAssertionStatus(className: String!, enabled: Boolean) Sets the desired assertion status for the named top-level class in this class loader and any nested classes contained therein. |
open Unit |
setDefaultAssertionStatus(enabled: Boolean) Sets the default assertion status for this class loader. |
open Unit |
setPackageAssertionStatus(packageName: String!, enabled: Boolean) Sets the package default assertion status for the named package. |
Protected methods | |
---|---|
Class<*>! |
defineClass(b: ByteArray!, off: Int, len: Int) Converts an array of bytes into an instance of class |
Class<*>! |
defineClass(name: String!, b: ByteArray!, off: Int, len: Int) Converts an array of bytes into an instance of class |
Class<*>! |
defineClass(name: String!, b: ByteArray!, off: Int, len: Int, protectionDomain: ProtectionDomain!) Converts an array of bytes into an instance of class |
Class<*>! |
defineClass(name: String!, b: ByteBuffer!, protectionDomain: ProtectionDomain!) Converts a |
open Package! |
definePackage(name: String!, specTitle: String!, specVersion: String!, specVendor: String!, implTitle: String!, implVersion: String!, implVendor: String!, sealBase: URL!) Defines a package by name in this |
open Class<*>! |
Finds the class with the specified binary name. |
open String! |
findLibrary(libname: String!) Returns the absolute path name of a native library. |
Class<*>! |
findLoadedClass(name: String!) Returns the class with the given binary name if this loader has been recorded by the Java virtual machine as an initiating loader of a class with that binary name. |
open URL! |
findResource(name: String!) Finds the resource with the given name. |
open Enumeration<URL!>! |
findResources(name: String!) Returns an enumeration of |
Class<*>! |
findSystemClass(name: String!) Finds a class with the specified binary name, loading it if necessary. |
open Package! |
getPackage(name: String!) Finds a package by name in this class loader and its ancestors. |
open Array<Package!>! |
Returns all of the |
open Class<*>! |
Loads the class with the specified binary name. |
open static Boolean |
Registers the caller as |
Unit |
resolveClass(c: Class<*>!) Links the specified class. |
Unit |
setSigners(c: Class<*>!, signers: Array<Any!>!) Sets the signers of a class. |
Protected constructors
ClassLoader
protected ClassLoader(parent: ClassLoader!)
Creates a new class loader using the specified parent class loader for delegation.
If there is a security manager, its checkCreateClassLoader
method is invoked. This may result in a security exception.
Parameters | |
---|---|
parent |
ClassLoader!: The parent class loader |
Exceptions | |
---|---|
java.lang.SecurityException |
If a security manager exists and its checkCreateClassLoader method doesn't allow creation of a new class loader. |
ClassLoader
protected ClassLoader()
Creates a new class loader using the ClassLoader
returned by the method getSystemClassLoader()
as the parent class loader.
If there is a security manager, its checkCreateClassLoader
method is invoked. This may result in a security exception.
Exceptions | |
---|---|
java.lang.SecurityException |
If a security manager exists and its checkCreateClassLoader method doesn't allow creation of a new class loader. |
Public methods
clearAssertionStatus
open fun clearAssertionStatus(): Unit
Sets the default assertion status for this class loader to false
and discards any package defaults or class assertion status settings associated with the class loader. This method is provided so that class loaders can be made to ignore any command line or persistent assertion status settings and "start with a clean slate." Android-note: AssertionStatuses are unsupported. This method is a no-op.
getParent
fun getParent(): ClassLoader!
Returns the parent class loader for delegation. Some implementations may use null
to represent the bootstrap class loader. This method will return null
in such implementations if this class loader's parent is the bootstrap class loader.
Return | |
---|---|
ClassLoader! |
The parent ClassLoader |
Exceptions | |
---|---|
java.lang.SecurityException |
If a security manager is present, and the caller's class loader is not null and is not an ancestor of this class loader, and the caller does not have the RuntimePermission ("getClassLoader") |
getResource
open fun getResource(name: String!): URL!
Finds the resource with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.
The name of a resource is a '/
'-separated path name thatf identifies the resource.
Parameters | |
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name |
String!: The resource name |
Return | |
---|---|
URL! |
URL object for reading the resource; null if the resource could not be found, a URL could not be constructed to locate the resource, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager. |
Exceptions | |
---|---|
java.lang.NullPointerException |
If name is null |
getResourceAsStream
open fun getResourceAsStream(name: String!): InputStream!
Returns an input stream for reading the specified resource.
The search order is described in the documentation for getResource(java.lang.String)
.
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
InputStream! |
An input stream for reading the resource; null if the resource could not be found, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager. |
Exceptions | |
---|---|
java.lang.NullPointerException |
If name is null |
getResources
open fun getResources(name: String!): Enumeration<URL!>!
Finds all the resources with the given name. A resource is some data (images, audio, text, etc) that can be accessed by class code in a way that is independent of the location of the code.
The name of a resource is a /
-separated path name that identifies the resource.
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
Enumeration<URL!>! |
An enumeration of URL objects for the resource. If no resources could be found, the enumeration will be empty. Resources for which a URL cannot be constructed, are in a package that is not opened unconditionally, or access to the resource is denied by the security manager, are not returned in the enumeration. |
Exceptions | |
---|---|
java.io.IOException |
If I/O errors occur |
java.lang.NullPointerException |
If name is null |
getSystemClassLoader
open static fun getSystemClassLoader(): ClassLoader!
Returns the system class loader. This is the default delegation parent for new ClassLoader
instances, and is typically the class loader used to start the application.
This method is first invoked early in the runtime's startup sequence, at which point it creates the system class loader. This class loader will be the context class loader for the main application thread (for example, the thread that invokes the main
method of the main class).
The default system class loader is an implementation-dependent instance of this class.
Return | |
---|---|
ClassLoader! |
The system ClassLoader |
Exceptions | |
---|---|
java.lang.SecurityException |
If a security manager is present, and the caller's class loader is not null and is not the same as or an ancestor of the system class loader, and the caller does not have the RuntimePermission ("getClassLoader") |
java.lang.IllegalStateException |
If invoked recursively during the construction of the class loader specified by the "java.system.class.loader " property. |
java.lang.Error |
If the system property "java.system.class.loader " is defined but the named class could not be loaded, the provider class does not define the required constructor, or an exception is thrown by that constructor when it is invoked. The underlying cause of the error can be retrieved via the Throwable#getCause() method. |
getSystemResource
open static fun getSystemResource(name: String!): URL!
Find a resource of the specified name from the search path used to load classes. This method locates the resource through the system class loader (see getSystemClassLoader()
).
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
URL! |
A URL to the resource; null if the resource could not be found, a URL could not be constructed to locate the resource, the resource is in a package that is not opened unconditionally or access to the resource is denied by the security manager. |
getSystemResourceAsStream
open static fun getSystemResourceAsStream(name: String!): InputStream!
Open for reading, a resource of the specified name from the search path used to load classes. This method locates the resource through the system class loader (see getSystemClassLoader()
).
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
InputStream! |
An input stream for reading the resource; null if the resource could not be found, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager. |
getSystemResources
open static fun getSystemResources(name: String!): Enumeration<URL!>!
Finds all resources of the specified name from the search path used to load classes. The resources thus found are returned as an Enumeration
of objects.
The search order is described in the documentation for getSystemResource(java.lang.String)
.
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
Enumeration<URL!>! |
An enumeration of URL objects for the resource. If no resources could be found, the enumeration will be empty. Resources for which a URL cannot be constructed, are in a package that is not opened unconditionally, or access to the resource is denied by the security manager, are not returned in the enumeration. |
Exceptions | |
---|---|
java.io.IOException |
If I/O errors occur |
loadClass
open fun loadClass(name: String!): Class<*>!
Loads the class with the specified binary name. This method searches for classes in the same manner as the loadClass(java.lang.String,boolean)
method. It is invoked by the Java virtual machine to resolve class references. Invoking this method is equivalent to invoking loadClass(name,
.
Parameters | |
---|---|
name |
String!: The binary name of the class |
Return | |
---|---|
Class<*>! |
The resulting Class object |
Exceptions | |
---|---|
java.lang.ClassNotFoundException |
If the class was not found |
setClassAssertionStatus
open fun setClassAssertionStatus(
className: String!,
enabled: Boolean
): Unit
Sets the desired assertion status for the named top-level class in this class loader and any nested classes contained therein. This setting takes precedence over the class loader's default assertion status, and over any applicable per-package default. This method has no effect if the named class has already been initialized. (Once a class is initialized, its assertion status cannot change.)
If the named class is not a top-level class, this invocation will have no effect on the actual assertion status of any class.
Android-note: AssertionStatuses are unsupported. This method is a no-op.Parameters | |
---|---|
className |
String!: The fully qualified class name of the top-level class whose assertion status is to be set. |
enabled |
Boolean: true if the named class is to have assertions enabled when (and if) it is initialized, false if the class is to have assertions disabled. |
setDefaultAssertionStatus
open fun setDefaultAssertionStatus(enabled: Boolean): Unit
Sets the default assertion status for this class loader. This setting determines whether classes loaded by this class loader and initialized in the future will have assertions enabled or disabled by default. This setting may be overridden on a per-package or per-class basis by invoking setPackageAssertionStatus(java.lang.String,boolean)
or setClassAssertionStatus(java.lang.String,boolean)
. Android-note: AssertionStatuses are unsupported. This method is a no-op.
Parameters | |
---|---|
enabled |
Boolean: true if classes loaded by this class loader will henceforth have assertions enabled by default, false if they will have assertions disabled by default. |
setPackageAssertionStatus
open fun setPackageAssertionStatus(
packageName: String!,
enabled: Boolean
): Unit
Sets the package default assertion status for the named package. The package default assertion status determines the assertion status for classes initialized in the future that belong to the named package or any of its "subpackages".
A subpackage of a package named p is any package whose name begins with "p.
". For example, javax.swing.text
is a subpackage of javax.swing
, and both java.util
and java.lang.reflect
are subpackages of java
.
In the event that multiple package defaults apply to a given class, the package default pertaining to the most specific package takes precedence over the others. For example, if javax.lang
and javax.lang.reflect
both have package defaults associated with them, the latter package default applies to classes in javax.lang.reflect
.
Package defaults take precedence over the class loader's default assertion status, and may be overridden on a per-class basis by invoking setClassAssertionStatus(java.lang.String,boolean)
.
Parameters | |
---|---|
packageName |
String!: The name of the package whose package default assertion status is to be set. A null value indicates the unnamed package that is "current" (see section {@jls 7.4.2} of The Java Language Specification.) |
enabled |
Boolean: true if classes loaded by this classloader and belonging to the named package or any of its subpackages will have assertions enabled by default, false if they will have assertions disabled by default. |
Protected methods
defineClass
protected fundefineClass(
b: ByteArray!,
off: Int,
len: Int
): Class<*>!
Deprecated: Replaced by defineClass(String, byte[], int, int)
Converts an array of bytes into an instance of class Class
. Before the Class
can be used it must be resolved. This method is deprecated in favor of the version that takes a binary name as its first argument, and is more secure.
Parameters | |
---|---|
b |
ByteArray!: The bytes that make up the class data. The bytes in positions off through off+len-1 should have the format of a valid class file as defined by The Java Virtual Machine Specification. |
off |
Int: The start offset in b of the class data |
len |
Int: The length of the class data |
Return | |
---|---|
Class<*>! |
The Class object that was created from the specified class data |
Exceptions | |
---|---|
java.lang.ClassFormatError |
If the data did not contain a valid class |
java.lang.IndexOutOfBoundsException |
If either off or len is negative, or if off+len is greater than b.length . |
java.lang.SecurityException |
If an attempt is made to add this class to a package that contains classes that were signed by a different set of certificates than this class, or if an attempt is made to define a class in a package with a fully-qualified name that starts with "java. ". |
defineClass
protected fun defineClass(
name: String!,
b: ByteArray!,
off: Int,
len: Int
): Class<*>!
Converts an array of bytes into an instance of class Class
. Before the Class
can be used it must be resolved.
This method assigns a default ProtectionDomain
to the newly defined class. The ProtectionDomain
is effectively granted the same set of permissions returned when Policy.getPolicy().getPermissions(new CodeSource(null, null))
is invoked. The default protection domain is created on the first invocation of defineClass
, and re-used on subsequent invocations.
To assign a specific ProtectionDomain
to the class, use the defineClass
method that takes a ProtectionDomain
as one of its arguments.
This method defines a package in this class loader corresponding to the package of the Class
(if such a package has not already been defined in this class loader). The name of the defined package is derived from the binary name of the class specified by the byte array b
. Other properties of the defined package are as specified by Package
.
Parameters | |
---|---|
name |
String!: The expected binary name of the class, or null if not known |
b |
ByteArray!: The bytes that make up the class data. The bytes in positions off through off+len-1 should have the format of a valid class file as defined by The Java Virtual Machine Specification. |
off |
Int: The start offset in b of the class data |
len |
Int: The length of the class data |
Return | |
---|---|
Class<*>! |
The Class object that was created from the specified class data. |
Exceptions | |
---|---|
java.lang.ClassFormatError |
If the data did not contain a valid class |
java.lang.IndexOutOfBoundsException |
If either off or len is negative, or if off+len is greater than b.length . |
java.lang.SecurityException |
If an attempt is made to add this class to a package that contains classes that were signed by a different set of certificates than this class (which is unsigned), or if name begins with "java. ". |
defineClass
protected fun defineClass(
name: String!,
b: ByteArray!,
off: Int,
len: Int,
protectionDomain: ProtectionDomain!
): Class<*>!
Converts an array of bytes into an instance of class Class
, with a given ProtectionDomain
.
If the given ProtectionDomain
is null
, then a default protection domain will be assigned to the class as specified in the documentation for defineClass(java.lang.String,byte[],int,int)
. Before the class can be used it must be resolved.
The first class defined in a package determines the exact set of certificates that all subsequent classes defined in that package must contain. The set of certificates for a class is obtained from the CodeSource
within the ProtectionDomain
of the class. Any classes added to that package must contain the same set of certificates or a SecurityException
will be thrown. Note that if name
is null
, this check is not performed. You should always pass in the binary name of the class you are defining as well as the bytes. This ensures that the class you are defining is indeed the class you think it is.
This method defines a package in this class loader corresponding to the package of the Class
(if such a package has not already been defined in this class loader). The name of the defined package is derived from the binary name of the class specified by the byte array b
. Other properties of the defined package are as specified by Package
.
Parameters | |
---|---|
name |
String!: The expected binary name of the class, or null if not known |
b |
ByteArray!: The bytes that make up the class data. The bytes in positions off through off+len-1 should have the format of a valid class file as defined by The Java Virtual Machine Specification. |
off |
Int: The start offset in b of the class data |
len |
Int: The length of the class data |
protectionDomain |
ProtectionDomain!: The ProtectionDomain of the class |
Return | |
---|---|
Class<*>! |
The Class object created from the data, and ProtectionDomain . |
Exceptions | |
---|---|
java.lang.ClassFormatError |
If the data did not contain a valid class |
java.lang.NoClassDefFoundError |
If name is not null and not equal to the binary name of the class specified by b |
java.lang.IndexOutOfBoundsException |
If either off or len is negative, or if off+len is greater than b.length . |
java.lang.SecurityException |
If an attempt is made to add this class to a package that contains classes that were signed by a different set of certificates than this class, or if name begins with "java. " and this class loader is not the platform class loader or its ancestor. |
defineClass
protected fun defineClass(
name: String!,
b: ByteBuffer!,
protectionDomain: ProtectionDomain!
): Class<*>!
Converts a ByteBuffer
into an instance of class Class
, with the given ProtectionDomain
. If the given ProtectionDomain
is null
, then a default protection domain will be assigned to the class as specified in the documentation for defineClass(java.lang.String,byte[],int,int)
. Before the class can be used it must be resolved.
The rules about the first class defined in a package determining the set of certificates for the package, the restrictions on class names, and the defined package of the class are identical to those specified in the documentation for defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
.
An invocation of this method of the form cl.defineClass(
name,
bBuffer,
pd)
yields exactly the same result as the statements
...
byte[] temp = new byte[bBuffer.remaining
()];
bBuffer. get
(temp);
return cl.defineClass
(name, temp, 0, temp.length, pd);
Parameters | |
---|---|
name |
String!: The expected binary name. of the class, or null if not known |
b |
ByteBuffer!: The bytes that make up the class data. The bytes from positions b.position() through b.position() + b.limit() -1 should have the format of a valid class file as defined by The Java Virtual Machine Specification. |
protectionDomain |
ProtectionDomain!: The ProtectionDomain of the class, or null . |
Return | |
---|---|
Class<*>! |
The Class object created from the data, and ProtectionDomain . |
Exceptions | |
---|---|
java.lang.ClassFormatError |
If the data did not contain a valid class. |
java.lang.NoClassDefFoundError |
If name is not null and not equal to the binary name of the class specified by b |
java.lang.SecurityException |
If an attempt is made to add this class to a package that contains classes that were signed by a different set of certificates than this class, or if name begins with "java. ". |
definePackage
protected open fun definePackage(
name: String!,
specTitle: String!,
specVersion: String!,
specVendor: String!,
implTitle: String!,
implVersion: String!,
implVendor: String!,
sealBase: URL!
): Package!
Defines a package by name in this ClassLoader
.
Package names must be unique within a class loader and cannot be redefined or changed once created.
If a class loader wishes to define a package with specific properties, such as version information, then the class loader should call this definePackage
method before calling defineClass
. Otherwise, the defineClass
method will define a package in this class loader corresponding to the package of the newly defined class; the properties of this defined package are specified by Package
.
Parameters | |
---|---|
name |
String!: The package name |
specTitle |
String!: The specification title |
specVersion |
String!: The specification version |
specVendor |
String!: The specification vendor |
implTitle |
String!: The implementation title |
implVersion |
String!: The implementation version |
implVendor |
String!: The implementation vendor |
sealBase |
URL!: If not null , then this package is sealed with respect to the given code source URL object. Otherwise, the package is not sealed. |
Return | |
---|---|
Package! |
The newly defined Package object |
Exceptions | |
---|---|
java.lang.NullPointerException |
if name is null . |
java.lang.IllegalArgumentException |
if a package of the given name is already defined by this class loader |
See Also
findClass
protected open fun findClass(name: String!): Class<*>!
Finds the class with the specified binary name. This method should be overridden by class loader implementations that follow the delegation model for loading classes, and will be invoked by the #loadClass method after checking the parent class loader for the requested class.
Parameters | |
---|---|
name |
String!: The binary name of the class |
Return | |
---|---|
Class<*>! |
The resulting Class object |
Exceptions | |
---|---|
java.lang.ClassNotFoundException |
If the class could not be found |
findLibrary
protected open fun findLibrary(libname: String!): String!
Returns the absolute path name of a native library. The VM invokes this method to locate the native libraries that belong to classes loaded with this class loader. If this method returns null
, the VM searches the library along the path specified as the "java.library.path
" property.
Parameters | |
---|---|
libname |
String!: The library name |
Return | |
---|---|
String! |
The absolute path of the native library |
findLoadedClass
protected fun findLoadedClass(name: String!): Class<*>!
Returns the class with the given binary name if this loader has been recorded by the Java virtual machine as an initiating loader of a class with that binary name. Otherwise null
is returned.
Parameters | |
---|---|
name |
String!: The binary name of the class |
Return | |
---|---|
Class<*>! |
The Class object, or null if the class has not been loaded |
findResource
protected open fun findResource(name: String!): URL!
Finds the resource with the given name. Class loader implementations should override this method.
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
URL! |
URL object for reading the resource; null if the resource could not be found, a URL could not be constructed to locate the resource, the resource is in a package that is not opened unconditionally, or access to the resource is denied by the security manager. |
findResources
protected open fun findResources(name: String!): Enumeration<URL!>!
Returns an enumeration of URL
objects representing all the resources with the given name. Class loader implementations should override this method.
Parameters | |
---|---|
name |
String!: The resource name |
Return | |
---|---|
Enumeration<URL!>! |
An enumeration of URL objects for the resource. If no resources could be found, the enumeration will be empty. Resources for which a URL cannot be constructed, are in a package that is not opened unconditionally, or access to the resource is denied by the security manager, are not returned in the enumeration. |
Exceptions | |
---|---|
java.io.IOException |
If I/O errors occur |
findSystemClass
protected fun findSystemClass(name: String!): Class<*>!
Finds a class with the specified binary name, loading it if necessary.
This method loads the class through the system class loader (see getSystemClassLoader()
). The Class
object returned might have more than one ClassLoader
associated with it. Subclasses of ClassLoader
need not usually invoke this method, because most class loaders need to override just findClass(java.lang.String)
.
Parameters | |
---|---|
name |
String!: The binary name of the class |
Return | |
---|---|
Class<*>! |
The Class object for the specified name |
Exceptions | |
---|---|
java.lang.ClassNotFoundException |
If the class could not be found |
See Also
getPackage
protected open fungetPackage(name: String!): Package!
Deprecated: If multiple class loaders delegate to each other and define classes with the same package name, and one such loader relies on the lookup behavior of getPackage
to return a Package
from a parent loader, then the properties exposed by the Package
may not be as expected in the rest of the program. For example, the Package
will only expose annotations from the package-info.class
file defined by the parent loader, even if annotations exist in a package-info.class
file defined by a child loader.
Finds a package by name in this class loader and its ancestors.
If this class loader defines a Package
of the given name, the Package
is returned. Otherwise, the ancestors of this class loader are searched recursively (parent by parent) for a Package
of the given name.
Parameters | |
---|---|
name |
String!: The package name |
Return | |
---|---|
Package! |
The Package of the given name that has been defined by this class loader or its ancestors, or null if not found. |
Exceptions | |
---|---|
java.lang.NullPointerException |
if name is null . |
getPackages
protected open fun getPackages(): Array<Package!>!
Returns all of the Package
s that have been defined by this class loader and its ancestors. The returned array may contain more than one Package
object of the same package name, each defined by a different class loader in the class loader hierarchy.
Return | |
---|---|
Array<Package!>! |
The array of Package objects that have been defined by this class loader and its ancestors |
loadClass
protected open fun loadClass(
name: String!,
resolve: Boolean
): Class<*>!
Loads the class with the specified binary name. The default implementation of this method searches for classes in the following order:
- Invoke
findLoadedClass(java.lang.String)
to check if the class has already been loaded. - Invoke the
loadClass
method on the parent class loader. If the parent isnull
the class loader built into the virtual machine is used, instead. - Invoke the
findClass(java.lang.String)
method to find the class.
If the class was found using the above steps, and the resolve
flag is true, this method will then invoke the resolveClass(java.lang.Class)
method on the resulting Class
object.
Subclasses of ClassLoader
are encouraged to override findClass(java.lang.String)
, rather than this method.
Parameters | |
---|---|
name |
String!: The binary name of the class |
resolve |
Boolean: If true then resolve the class |
Return | |
---|---|
Class<*>! |
The resulting Class object |
Exceptions | |
---|---|
java.lang.ClassNotFoundException |
If the class could not be found |
registerAsParallelCapable
protected open static fun registerAsParallelCapable(): Boolean
Registers the caller as isRegisteredAsParallelCapable() parallel capable
. The registration succeeds if and only if all of the following conditions are met:
- no instance of the caller has been created
- all of the super classes (except class Object) of the caller are registered as parallel capable
Note that once a class loader is registered as parallel capable, there is no way to change it back.
Return | |
---|---|
Boolean |
true if the caller is successfully registered as parallel capable and false if otherwise. |
resolveClass
protected fun resolveClass(c: Class<*>!): Unit
Links the specified class. This (misleadingly named) method may be used by a class loader to link a class. If the class c
has already been linked, then this method simply returns. Otherwise, the class is linked as described in the "Execution" chapter of The Java Language Specification.
Parameters | |
---|---|
c |
Class<*>!: The class to link |
Exceptions | |
---|---|
java.lang.NullPointerException |
If c is null . |
setSigners
protected fun setSigners(
c: Class<*>!,
signers: Array<Any!>!
): Unit
Sets the signers of a class. This should be invoked after defining a class.
Parameters | |
---|---|
c |
Class<*>!: The Class object |
signers |
Array<Any!>!: The signers for the class |