Source Code Cross Referenced for Capabilities.java in  » Swing-Library » jEdit » org » gjt » sp » jedit » bsh » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Swing Library » jEdit » org.gjt.sp.jedit.bsh 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*****************************************************************************
002:         *                                                                           *
003:         *  This file is part of the BeanShell Java Scripting distribution.          *
004:         *  Documentation and updates may be found at http://www.beanshell.org/      *
005:         *                                                                           *
006:         *  Sun Public License Notice:                                               *
007:         *                                                                           *
008:         *  The contents of this file are subject to the Sun Public License Version  *
009:         *  1.0 (the "License"); you may not use this file except in compliance with *
010:         *  the License. A copy of the License is available at http://www.sun.com    * 
011:         *                                                                           *
012:         *  The Original Code is BeanShell. The Initial Developer of the Original    *
013:         *  Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright     *
014:         *  (C) 2000.  All Rights Reserved.                                          *
015:         *                                                                           *
016:         *  GNU Public License Notice:                                               *
017:         *                                                                           *
018:         *  Alternatively, the contents of this file may be used under the terms of  *
019:         *  the GNU Lesser General Public License (the "LGPL"), in which case the    *
020:         *  provisions of LGPL are applicable instead of those above. If you wish to *
021:         *  allow use of your version of this file only under the  terms of the LGPL *
022:         *  and not to allow others to use your version of this file under the SPL,  *
023:         *  indicate your decision by deleting the provisions above and replace      *
024:         *  them with the notice and other provisions required by the LGPL.  If you  *
025:         *  do not delete the provisions above, a recipient may use your version of  *
026:         *  this file under either the SPL or the LGPL.                              *
027:         *                                                                           *
028:         *  Patrick Niemeyer (pat@pat.net)                                           *
029:         *  Author of Learning Java, O'Reilly & Associates                           *
030:         *  http://www.pat.net/~pat/                                                 *
031:         *                                                                           *
032:         *****************************************************************************/package org.gjt.sp.jedit.bsh;
033:
034:        import java.util.Hashtable;
035:
036:        /**
037:         The map of extended features supported by the runtime in which we live.
038:         <p>
039:
040:         This class should be independent of all other bsh classes!
041:         <p>
042:
043:         Note that tests for class existence here do *not* use the 
044:         BshClassManager, as it may require other optional class files to be 
045:         loaded.  
046:         */
047:        public class Capabilities {
048:            private static boolean accessibility = false;
049:
050:            public static boolean haveSwing() {
051:                // classExists caches info for us
052:                return classExists("javax.swing.JButton");
053:            }
054:
055:            public static boolean canGenerateInterfaces() {
056:                // classExists caches info for us
057:                return classExists("java.lang.reflect.Proxy");
058:            }
059:
060:            /**
061:            	If accessibility is enabled
062:            	determine if the accessibility mechanism exists and if we have
063:            	the optional bsh package to use it.
064:            	Note that even if both are true it does not necessarily mean that we 
065:            	have runtime permission to access the fields... Java security has
066:             	a say in it.
067:            	@see org.gjt.sp.jedit.bsh.ReflectManager
068:             */
069:            public static boolean haveAccessibility() {
070:                return accessibility;
071:            }
072:
073:            public static void setAccessibility(boolean b) throws Unavailable {
074:                if (b == false) {
075:                    accessibility = false;
076:                    return;
077:                }
078:
079:                if (!classExists("java.lang.reflect.AccessibleObject")
080:                        || !classExists("org.gjt.sp.jedit.bsh.reflect.ReflectManagerImpl"))
081:                    throw new Unavailable("Accessibility unavailable");
082:
083:                // test basic access
084:                try {
085:                    String.class.getDeclaredMethods();
086:                } catch (SecurityException e) {
087:                    throw new Unavailable("Accessibility unavailable: " + e);
088:                }
089:
090:                accessibility = true;
091:            }
092:
093:            private static Hashtable classes = new Hashtable();
094:
095:            /**
096:            	Use direct Class.forName() to test for the existence of a class.
097:            	We should not use BshClassManager here because:
098:            		a) the systems using these tests would probably not load the
099:            		classes through it anyway.
100:            		b) bshclassmanager is heavy and touches other class files.  
101:            		this capabilities code must be light enough to be used by any
102:            		system **including the remote applet**.
103:             */
104:            public static boolean classExists(String name) {
105:                Object c = classes.get(name);
106:
107:                if (c == null) {
108:                    try {
109:                        /*
110:                        	Note: do *not* change this to 
111:                        	BshClassManager plainClassForName() or equivalent.
112:                        	This class must not touch any other bsh classes.
113:                         */
114:                        c = Class.forName(name);
115:                    } catch (ClassNotFoundException e) {
116:                    }
117:
118:                    if (c != null)
119:                        classes.put(c, "unused");
120:                }
121:
122:                return c != null;
123:            }
124:
125:            /**
126:            	An attempt was made to use an unavailable capability supported by
127:            	an optional package.  The normal operation is to test before attempting
128:            	to use these packages... so this is runtime exception.
129:             */
130:            public static class Unavailable extends UtilEvalError {
131:                public Unavailable(String s) {
132:                    super(s);
133:                }
134:            }
135:        }
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