Added a rule that allows for object validation before it is passed up to

its parent. Useful for making sure an object was fully parsed before
throwing it into the mix.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@483 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/xml/ValidatedSetNextRule.java

@@ -0,0 +1,121 @@
+//
+// $Id: ValidatedSetNextRule.java,v 1.1 2001/11/29 21:30:13 mdb Exp $
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2001 Walter Korman
+// 
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.xml;
+
+import java.lang.reflect.Method;
+
+import org.xml.sax.Attributes;
+import org.apache.commons.digester.Digester;
+import org.apache.commons.digester.Rule;
+
+/**
+ * Like the <code>SetNextRule</code> except that the object on the top of
+ * the stack is validated before the set next method is called. If the
+ * object is determined not to be valid, the set next method will not be
+ * called (and the assumption is that the validator will have emmitted
+ * some useful error message indicating to the user why the object was
+ * invalid).
+ */
+public class ValidatedSetNextRule extends Rule
+{
+    /**
+     * An implementor if this interface will be used to determine whether
+     * the object on the top of the stack is valid before it is "set
+     * next"ed. If the object is not valid, it will not be "set next"ed.
+     */
+    public static interface Validator
+    {
+        /**
+         * Returns true if the object in question is valid (was properly
+         * parsed), false if it is not.
+         */
+        public boolean isValid (Object target);
+    }
+
+    /**
+     * Constructs a set method rule for the specified method.
+     */
+    public ValidatedSetNextRule (Digester digester, String methodName,
+                                 Validator validator)
+    {
+        this(digester, methodName, null, validator);
+    }
+
+    /**
+     * Constructs a set method rule for the specified method with the
+     * specified parameter type.
+     */
+    public ValidatedSetNextRule (Digester digester, String methodName,
+                                 Class paramType, Validator validator)
+    {
+        super(digester);
+
+        // keep this for later
+        _methodName = methodName;
+        _paramType = paramType;
+        _validator = validator;
+    }
+
+    public void end ()
+        throws Exception
+    {
+	// identify the objects to be used
+	Object child = digester.peek(0);
+	Object parent = digester.peek(1);
+
+        // make sure the object in question is valid
+        if (!_validator.isValid(child)) {
+            return;
+        }
+
+        Class pclass = parent.getClass();
+	if (digester.getDebug() >= 1) {
+	    digester.log("Call " + pclass.getName() + "." + _methodName +
+                         " (" + child + ")");
+        }
+
+	// call the specified method
+	Class[] paramTypes = new Class[1];
+        paramTypes[0] = (_paramType == null) ? child.getClass() : _paramType;
+	Method method = parent.getClass().getMethod(_methodName, paramTypes);
+	method.invoke(parent, new Object[] { child });
+    }
+
+    /**
+     * Render a printable version of this rule.
+     */
+    public String toString ()
+    {
+        StringBuffer sb = new StringBuffer("ValidatedSetNextRule[");
+        sb.append("methodName=");
+        sb.append(_methodName);
+        if (_paramType != null) {
+            sb.append("paramType=");
+            sb.append(_paramType.getName());
+        }
+        sb.append("]");
+        return (sb.toString());
+    }
+
+    protected String _methodName;
+    protected Class _paramType;
+    protected Validator _validator;
+}