Class RMIClassLoader
- java.lang.Object
-
- java.rmi.server.RMIClassLoader
public class RMIClassLoader extends Object
RMIClassLoader
comprises static methods to support dynamic class loading with RMI. Included are methods for loading classes from a network location (one or more URLs) and obtaining the location from which an existing class should be loaded by remote parties. These methods are used by the RMI runtime when marshalling and unmarshalling classes contained in the arguments and return values of remote method calls, and they also may be invoked directly by applications in order to mimic RMI's dynamic class loading behavior.
The implementation of the following static methods
-
loadClass(URL,String)
-
loadClass(String,String)
-
loadClass(String,String,ClassLoader)
-
loadProxyClass(String,String[],ClassLoader)
-
getClassLoader(String)
-
getClassAnnotation(Class)
RMIClassLoaderSpi
, the service provider interface for those methods. When one of the methods is invoked, its behavior is to delegate to a corresponding method on the service provider instance. The details of how each method delegates to the provider instance is described in the documentation for each particular method. The service provider instance is chosen as follows:
- If the system property
java.rmi.server.RMIClassLoaderSpi
is defined, then if its value equals the string"default"
, the provider instance will be the value returned by an invocation of thegetDefaultProviderInstance()
method, and for any other value, if a class named with the value of the property can be loaded by the system class loader (seeClassLoader.getSystemClassLoader()
) and that class is assignable toRMIClassLoaderSpi
and has a public no-argument constructor, then that constructor will be invoked to create the provider instance. If the property is defined but any other of those conditions are not true, then an unspecifiedError
will be thrown to code that attempts to useRMIClassLoader
, indicating the failure to obtain a provider instance. - If a resource named
META-INF/services/java.rmi.server.RMIClassLoaderSpi
is visible to the system class loader, then the contents of that resource are interpreted as a provider-configuration file, and the first class name specified in that file is used as the provider class name. If a class with that name can be loaded by the system class loader and that class is assignable toRMIClassLoaderSpi
and has a public no-argument constructor, then that constructor will be invoked to create the provider instance. If the resource is found but a provider cannot be instantiated as described, then an unspecifiedError
will be thrown to code that attempts to useRMIClassLoader
, indicating the failure to obtain a provider instance. - Otherwise, the provider instance will be the value returned by an invocation of the
getDefaultProviderInstance()
method.
- Since:
- 1.1
- See Also:
RMIClassLoaderSpi
Method Summary
Modifier and Type | Method | Description |
---|---|---|
static String | getClassAnnotation(Class<?> cl) | Returns the annotation string (representing a location for the class definition) that RMI will use to annotate the class descriptor when marshalling objects of the given class. |
static ClassLoader | getClassLoader(String codebase) | Returns a class loader that loads classes from the given codebase URL path. |
static RMIClassLoaderSpi | getDefaultProviderInstance() | Returns the canonical instance of the default provider for the service provider interface |
static Object | getSecurityContext(ClassLoader loader) | Deprecated. no replacement. |
static Class<?> | loadClass(String name) | Deprecated. replaced by loadClass(String,String) method |
static Class<?> | loadClass(String codebase,
String name) | Loads a class from a codebase URL path. |
static Class<?> | loadClass(String codebase,
String name,
ClassLoader defaultLoader) | Loads a class from a codebase URL path, optionally using the supplied loader. |
static Class<?> | loadClass(URL codebase,
String name) | Loads a class from a codebase URL. |
static Class<?> | loadProxyClass(String codebase,
String[] interfaces,
ClassLoader defaultLoader) | Loads a dynamic proxy class (see |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Method Detail
loadClass
@Deprecated public static Class<?> loadClass(String name) throws MalformedURLException, ClassNotFoundException
loadClass(String,String)
methodLoads the class with the specified name
.
This method delegates to loadClass(String,String)
, passing null
as the first argument and name
as the second argument.
- Parameters:
-
name
- the name of the class to load - Returns:
- the
Class
object representing the loaded class - Throws:
-
MalformedURLException
- if a provider-specific URL used to load classes is invalid -
ClassNotFoundException
- if a definition for the class could not be found at the codebase location - See Also:
loadClass(String,String)
loadClass
public static Class<?> loadClass(URL codebase, String name) throws MalformedURLException, ClassNotFoundException
Loads a class from a codebase URL. If codebase
is null
, then this method will behave the same as loadClass(String,String)
with a null
codebase
and the given class name.
This method delegates to the RMIClassLoaderSpi.loadClass(String,String,ClassLoader)
method of the provider instance, passing the result of invoking URL.toString()
on the given URL (or null
if codebase
is null) as the first argument, name
as the second argument, and null
as the third argument.
- Parameters:
-
codebase
- the URL to load the class from, ornull
-
name
- the name of the class to load - Returns:
- the
Class
object representing the loaded class - Throws:
-
MalformedURLException
- ifcodebase
isnull
and a provider-specific URL used to load classes is invalid -
ClassNotFoundException
- if a definition for the class could not be found at the specified URL
loadClass
public static Class<?> loadClass(String codebase, String name) throws MalformedURLException, ClassNotFoundException
Loads a class from a codebase URL path.
This method delegates to the RMIClassLoaderSpi.loadClass(String,String,ClassLoader)
method of the provider instance, passing codebase
as the first argument, name
as the second argument, and null
as the third argument.
- Parameters:
-
codebase
- the list of URLs (separated by spaces) to load the class from, ornull
-
name
- the name of the class to load - Returns:
- the
Class
object representing the loaded class - Throws:
-
MalformedURLException
- ifcodebase
is non-null
and contains an invalid URL, or ifcodebase
isnull
and a provider-specific URL used to load classes is invalid -
ClassNotFoundException
- if a definition for the class could not be found at the specified location - Since:
- 1.2
loadClass
public static Class<?> loadClass(String codebase, String name, ClassLoader defaultLoader) throws MalformedURLException, ClassNotFoundException
Loads a class from a codebase URL path, optionally using the supplied loader. This method should be used when the caller would like to make available to the provider implementation an additional contextual class loader to consider, such as the loader of a caller on the stack. Typically, a provider implementation will attempt to resolve the named class using the given defaultLoader
, if specified, before attempting to resolve the class from the codebase URL path.
This method delegates to the RMIClassLoaderSpi.loadClass(String,String,ClassLoader)
method of the provider instance, passing codebase
as the first argument, name
as the second argument, and defaultLoader
as the third argument.
- Parameters:
-
codebase
- the list of URLs (separated by spaces) to load the class from, ornull
-
name
- the name of the class to load -
defaultLoader
- additional contextual class loader to use, ornull
- Returns:
- the
Class
object representing the loaded class - Throws:
-
MalformedURLException
- ifcodebase
is non-null
and contains an invalid URL, or ifcodebase
isnull
and a provider-specific URL used to load classes is invalid -
ClassNotFoundException
- if a definition for the class could not be found at the specified location - Since:
- 1.4
loadProxyClass
public static Class<?> loadProxyClass(String codebase, String[] interfaces, ClassLoader defaultLoader) throws ClassNotFoundException, MalformedURLException
Loads a dynamic proxy class (see Proxy
) that implements a set of interfaces with the given names from a codebase URL path.
The interfaces will be resolved similar to classes loaded via the loadClass(String,String)
method using the given codebase
.
This method delegates to the RMIClassLoaderSpi.loadProxyClass(String,String[],ClassLoader)
method of the provider instance, passing codebase
as the first argument, interfaces
as the second argument, and defaultLoader
as the third argument.
- Parameters:
-
codebase
- the list of URLs (space-separated) to load classes from, ornull
-
interfaces
- the names of the interfaces for the proxy class to implement -
defaultLoader
- additional contextual class loader to use, ornull
- Returns:
- a dynamic proxy class that implements the named interfaces
- Throws:
-
MalformedURLException
- ifcodebase
is non-null
and contains an invalid URL, or ifcodebase
isnull
and a provider-specific URL used to load classes is invalid -
ClassNotFoundException
- if a definition for one of the named interfaces could not be found at the specified location, or if creation of the dynamic proxy class failed (such as ifProxy.getProxyClass(ClassLoader,Class[])
would throw anIllegalArgumentException
for the given interface list) - Since:
- 1.4
getClassLoader
public static ClassLoader getClassLoader(String codebase) throws MalformedURLException, SecurityException
Returns a class loader that loads classes from the given codebase URL path.
The class loader returned is the class loader that the loadClass(String,String)
method would use to load classes for the same codebase
argument.
This method delegates to the RMIClassLoaderSpi.getClassLoader(String)
method of the provider instance, passing codebase
as the argument.
If there is a security manger, its checkPermission
method will be invoked with a RuntimePermission("getClassLoader")
permission; this could result in a SecurityException
. The provider implementation of this method may also perform further security checks to verify that the calling context has permission to connect to all of the URLs in the codebase URL path.
- Parameters:
-
codebase
- the list of URLs (space-separated) from which the returned class loader will load classes from, ornull
- Returns:
- a class loader that loads classes from the given codebase URL path
- Throws:
-
MalformedURLException
- ifcodebase
is non-null
and contains an invalid URL, or ifcodebase
isnull
and a provider-specific URL used to identify the class loader is invalid -
SecurityException
- if there is a security manager and the invocation of itscheckPermission
method fails, or if the caller does not have permission to connect to all of the URLs in the codebase URL path - Since:
- 1.3
getClassAnnotation
public static String getClassAnnotation(Class<?> cl)
Returns the annotation string (representing a location for the class definition) that RMI will use to annotate the class descriptor when marshalling objects of the given class.
This method delegates to the RMIClassLoaderSpi.getClassAnnotation(Class)
method of the provider instance, passing cl
as the argument.
- Parameters:
-
cl
- the class to obtain the annotation for - Returns:
- a string to be used to annotate the given class when it gets marshalled, or
null
- Throws:
-
NullPointerException
- ifcl
isnull
- Since:
- 1.2
getDefaultProviderInstance
public static RMIClassLoaderSpi getDefaultProviderInstance()
Returns the canonical instance of the default provider for the service provider interface RMIClassLoaderSpi
. If the system property java.rmi.server.RMIClassLoaderSpi
is not defined, then the RMIClassLoader
static methods
-
loadClass(URL,String)
-
loadClass(String,String)
-
loadClass(String,String,ClassLoader)
-
loadProxyClass(String,String[],ClassLoader)
-
getClassLoader(String)
-
getClassAnnotation(Class)
If there is a security manager, its checkPermission
method will be invoked with a RuntimePermission("setFactory")
permission; this could result in a SecurityException
.
The default service provider instance implements RMIClassLoaderSpi
as follows:
The
getClassAnnotation
method returns aString
representing the codebase URL path that a remote party should use to download the definition for the specified class. The format of the returned string is a path of URLs separated by spaces. The codebase string returned depends on the defining class loader of the specified class:
If the class loader is the system class loader (see
ClassLoader.getSystemClassLoader()
), a parent of the system class loader such as the loader used for installed extensions, or the bootstrap class loader (which may be represented bynull
), then the value of thejava.rmi.server.codebase
property (or possibly an earlier cached value) is returned, ornull
is returned if that property is not set.Otherwise, if the class loader is an instance of
URLClassLoader
, then the returned string is a space-separated list of the external forms of the URLs returned by invoking thegetURLs
methods of the loader. If theURLClassLoader
was created by this provider to service an invocation of itsloadClass
orloadProxyClass
methods, then no permissions are required to get the associated codebase string. If it is an arbitrary otherURLClassLoader
instance, then if there is a security manager, itscheckPermission
method will be invoked once for each URL returned by thegetURLs
method, with the permission returned by invokingopenConnection().getPermission()
on each URL; if any of those invocations throws aSecurityException
or anIOException
, then the value of thejava.rmi.server.codebase
property (or possibly an earlier cached value) is returned, ornull
is returned if that property is not set.Finally, if the class loader is not an instance of
URLClassLoader
, then the value of thejava.rmi.server.codebase
property (or possibly an earlier cached value) is returned, ornull
is returned if that property is not set.For the implementations of the methods described below, which all take a
String
parameter namedcodebase
that is a space-separated list of URLs, each invocation has an associated codebase loader that is identified using thecodebase
argument in conjunction with the current thread's context class loader (seeThread.getContextClassLoader()
). When there is a security manager, this provider maintains an internal table of class loader instances (which are at least instances ofURLClassLoader
) keyed by the pair of their parent class loader and their codebase URL path (an ordered list of URLs). If thecodebase
argument isnull
, the codebase URL path is the value of the system propertyjava.rmi.server.codebase
or possibly an earlier cached value. For a given codebase URL path passed as thecodebase
argument to an invocation of one of the below methods in a given context, the codebase loader is the loader in the table with the specified codebase URL path and the current thread's context class loader as its parent. If no such loader exists, then one is created and added to the table. The table does not maintain strong references to its contained loaders, in order to allow them and their defined classes to be garbage collected when not otherwise reachable. In order to prevent arbitrary untrusted code from being implicitly loaded into a virtual machine with no security manager, if there is no security manager set, the codebase loader is just the current thread's context class loader (the supplied codebase URL path is ignored, so remote class loading is disabled).The
getClassLoader
method returns the codebase loader for the specified codebase URL path. If there is a security manager, then if the calling context does not have permission to connect to all of the URLs in the codebase URL path, aSecurityException
will be thrown.The
loadClass
method attempts to load the class with the specified name as follows:If the defaultLoader argument is non-null, it first attempts to load the class with the specified name using the defaultLoader, such as by evaluating Class.forName(name, false, defaultLoader) If the class is successfully loaded from the defaultLoader, that class is returned. If an exception other than ClassNotFoundException is thrown, that exception is thrown to the caller. Next, the loadClass method attempts to load the class with the specified name using the codebase loader for the specified codebase URL path. If there is a security manager, then the calling context must have permission to connect to all of the URLs in the codebase URL path; otherwise, the current thread's context class loader will be used instead of the codebase loader.The
loadProxyClass
method attempts to return a dynamic proxy class with the named interface as follows:If the
defaultLoader
argument is non-null
and all of the named interfaces can be resolved through that loader, then,
- if all of the resolved interfaces are
public
, then it first attempts to obtain a dynamic proxy class (usingProxy.getProxyClass
) for the resolved interfaces defined in the codebase loader; if that attempt throws anIllegalArgumentException
, it then attempts to obtain a dynamic proxy class for the resolved interfaces defined in thedefaultLoader
. If both attempts throwIllegalArgumentException
, then this method throws aClassNotFoundException
. If any other exception is thrown, that exception is thrown to the caller.- if all of the non-
public
resolved interfaces are defined in the same class loader, then it attempts to obtain a dynamic proxy class for the resolved interfaces defined in that loader.- otherwise, a
LinkageError
is thrown (because a class that implements all of the specified interfaces cannot be defined in any loader).Otherwise, if all of the named interfaces can be resolved through the codebase loader, then,
- if all of the resolved interfaces are
public
, then it attempts to obtain a dynamic proxy class for the resolved interfaces in the codebase loader. If the attempt throws anIllegalArgumentException
, then this method throws aClassNotFoundException
.- if all of the non-
public
resolved interfaces are defined in the same class loader, then it attempts to obtain a dynamic proxy class for the resolved interfaces defined in that loader.- otherwise, a
LinkageError
is thrown (because a class that implements all of the specified interfaces cannot be defined in any loader).Otherwise, a
ClassNotFoundException
is thrown for one of the named interfaces that could not be resolved.
- Returns:
- the canonical instance of the default service provider
- Throws:
-
SecurityException
- if there is a security manager and the invocation of itscheckPermission
method fails - Since:
- 1.4
getSecurityContext
@Deprecated public static Object getSecurityContext(ClassLoader loader)
Returns the security context of the given class loader.
- Parameters:
-
loader
- a class loader from which to get the security context - Returns:
- the security context
- See Also:
SecurityManager.getSecurityContext()