[转]授权标准覆盖机制

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Endorsed Standards Override Mechanism

Introduction

An endorsed standard is a Java^TM API defined through a standards process other than the Java Community Process^SM (JCP^SM). Because endorsed standards are defined outside the JCP, it is anticipated that such standards may be revised between releases of the Java platform. In order to take advantage of new revisions to endorsed standards, developers and software vendors may use the Endorsed Standards Override Mechanism to provide newer versions of an endorsed standard than those included in the Java platform as released by Sun Microsystems.

Endorsed Standards Classes Deployment

Classes implementing newer versions of endorsed standards should be placed in JAR files. The system property java.endorsed.dirs specifies one or more directories that the Java runtime environment will search for such JAR files. If more than one directory path is specified by java.endorsed.dirs, they must be separated by File.pathSeparatorChar. If no value is set for java.endorsed.dirs, then Sun Microsystem's implementation of the Java platform looks for JAR files in a default standard location:

<java-home>\lib\endorsed          [Microsoft Windows]


<java-home>/lib/endorsed          [Solaris or Linux]

Here <java-home> refers to the directory where the runtime software is installed (which is the top-level directory of the J2SE Runtime Environment or the jre directory in the JDK).

The J2SE runtime environment will use classes in such JAR files to override the corresponding classes provided in the Java platform as shipped by Sun.

Endorsed Standards APIs

The endorsed standards for J2SE^TM 5.0 constitute all classes and interfaces that are defined in the packages listed below. Classes and interfaces defined in sub-packages of listed packages are not endorsed standards unless those sub-packages are themselves listed. The Endorsed Standards Override Mechanism may be used to override the J2SE platform packages in the list below, and these packages may be overridden only by versions of the endorsed standard that are newer than that provided by the Java platform as released by Sun. No other packages from the J2SE platform API specification may be overridden.

javax.rmi.CORBA 


org.omg.CORBA 


org.omg.CORBA.DynAnyPackage


org.omg.CORBA.ORBPackage


org.omg.CORBA.portable


org.omg.CORBA.TypeCodePackage


org.omg.CORBA_2_3 


org.omg.CORBA_2_3.portable


org.omg.CosNaming 


org.omg.CosNaming.NamingContextExtPackage


org.omg.CosNaming.NamingContextPackage


org.omg.Dynamic


org.omg.DynamicAny


org.omg.DynamicAny.DynAnyFactoryPackage


org.omg.DynamicAny.DynAnyPackage


org.omg.IOP


org.omg.IOP.CodecFactoryPackage


org.omg.IOP.CodecPackage


org.omg.Messaging


org.omg.PortableInterceptor


org.omg.PortableInterceptor.ORBInitInfoPackage


org.omg.PortableServer


org.omg.PortableServer.CurrentPackage


org.omg.PortableServer.POAManagerPackage


org.omg.PortableServer.POAPackage


org.omg.PortableServer.portable


org.omg.PortableServer.ServantLocatorPackage


org.omg.SendingContext


org.omg.stub.java.rmi 


org.w3c.dom


org.xml.sax


org.xml.sax.ext


org.xml.sax.helpers

In addition to the packages listed above, which are part of the J2SE specification, users of Sun's J2SE Reference Implementation may be allowed to use the Endorsed Standards Override Mechanism to override implementation-specific classes such as the org.w3c.dom sub-packages delivered in Sun's Reference Implementation. See the corresponding license for details.

其实就是把新的jar形式的API放到$JDK_HOME/jre/lib/endorsed目录中，以达到覆盖JDK中原有旧版的API的目的。

来源:http://java.sun.com/j2se/1.5.0/docs/guide/standards/