Java tutorial
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If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. */ package javax.activation; import java.io.*; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.security.AccessController; import java.security.PrivilegedAction; /** * The CommandInfo class is used by CommandMap implementations to * describe the results of command requests. It provides the requestor * with both the verb requested, as well as an instance of the * bean. There is also a method that will return the name of the * class that implements the command but <i>it is not guaranteed to * return a valid value</i>. The reason for this is to allow CommandMap * implmentations that subclass CommandInfo to provide special * behavior. For example a CommandMap could dynamically generate * JavaBeans. In this case, it might not be possible to create an * object with all the correct state information solely from the class * name. */ public class CommandInfo { private String verb; private String className; /** * The Constructor for CommandInfo. * @param verb The command verb this CommandInfo decribes. * @param className The command's fully qualified class name. */ public CommandInfo(String verb, String className) { this.verb = verb; this.className = className; } /** * Return the command verb. * * @return the command verb. */ public String getCommandName() { return verb; } /** * Return the command's class name. <i>This method MAY return null in * cases where a CommandMap subclassed CommandInfo for its * own purposes.</i> In other words, it might not be possible to * create the correct state in the command by merely knowing * its class name. <b>DO NOT DEPEND ON THIS METHOD RETURNING * A VALID VALUE!</b> * * @return The class name of the command, or <i>null</i> */ public String getCommandClass() { return className; } /** * Return the instantiated JavaBean component. * <p> * If the current runtime environment supports * {@link java.beans.Beans#instantiate Beans.instantiate}, * use it to instantiate the JavaBeans component. Otherwise, use * {@link java.lang.Class#forName Class.forName}. * <p> * The component class needs to be public. * On Java SE 9 and newer, if the component class is in a named module, * it needs to be in an exported package. * <p> * If the bean implements the <code>javax.activation.CommandObject</code> * interface, call its <code>setCommandContext</code> method. * <p> * If the DataHandler parameter is null, then the bean is * instantiated with no data. NOTE: this may be useful * if for some reason the DataHandler that is passed in * throws IOExceptions when this method attempts to * access its InputStream. It will allow the caller to * retrieve a reference to the bean if it can be * instantiated. * <p> * If the bean does NOT implement the CommandObject interface, * this method will check if it implements the * java.io.Externalizable interface. If it does, the bean's * readExternal method will be called if an InputStream * can be acquired from the DataHandler.<p> * * @param dh The DataHandler that describes the data to be * passed to the command. * @param loader The ClassLoader to be used to instantiate the bean. * @return The bean * @exception IOException for failures reading data * @exception ClassNotFoundException if command object class can't * be found * @see java.beans.Beans#instantiate * @see javax.activation.CommandObject */ public Object getCommandObject(DataHandler dh, ClassLoader loader) throws IOException, ClassNotFoundException { Object new_bean = null; // try to instantiate the bean new_bean = Beans.instantiate(loader, className); // if we got one and it is a CommandObject if (new_bean != null) { if (new_bean instanceof CommandObject) { ((CommandObject) new_bean).setCommandContext(verb, dh); } else if (new_bean instanceof Externalizable) { if (dh != null) { InputStream is = dh.getInputStream(); if (is != null) { ((Externalizable) new_bean).readExternal(new ObjectInputStream(is)); } } } } return new_bean; } /** * Helper class to invoke Beans.instantiate reflectively or the equivalent * with core reflection when module java.desktop is not readable. */ private static final class Beans { static final Method instantiateMethod; static { Method m; try { Class<?> c = Class.forName("java.beans.Beans"); m = c.getDeclaredMethod("instantiate", ClassLoader.class, String.class); } catch (ClassNotFoundException e) { m = null; } catch (NoSuchMethodException e) { m = null; } instantiateMethod = m; } /** * Equivalent to invoking java.beans.Beans.instantiate(loader, cn) */ static Object instantiate(ClassLoader loader, String cn) throws IOException, ClassNotFoundException { Exception exception; if (instantiateMethod != null) { // invoke Beans.instantiate try { return instantiateMethod.invoke(null, loader, cn); } catch (InvocationTargetException e) { exception = e; } catch (IllegalAccessException e) { exception = e; } } else { SecurityManager security = System.getSecurityManager(); if (security != null) { // if it's ok with the SecurityManager, it's ok with me. String cname = cn.replace('/', '.'); if (cname.startsWith("[")) { int b = cname.lastIndexOf('[') + 2; if (b > 1 && b < cname.length()) { cname = cname.substring(b); } } int i = cname.lastIndexOf('.'); if (i != -1) { security.checkPackageAccess(cname.substring(0, i)); } } // Beans.instantiate specified to use SCL when loader is null if (loader == null) { loader = (ClassLoader) AccessController.doPrivileged(new PrivilegedAction() { public Object run() { ClassLoader cl = null; try { cl = ClassLoader.getSystemClassLoader(); } catch (SecurityException ex) { } return cl; } }); } Class<?> beanClass = Class.forName(cn, true, loader); try { return beanClass.newInstance(); } catch (Exception ex) { throw new ClassNotFoundException(beanClass + ": " + ex, ex); } } return null; } } }