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Java example source code file (SOQLEngine.java)

This example Java source code file (SOQLEngine.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

boolean, heapvisitor, instanceklass, jsjavafactory, jsjavaobject, object, objectreader, objectvisitor, runtimeexception, soqlengine, soqlexception, string, stringbuffer, stringtokenizer, util

The SOQLEngine.java Java example source code

/*
 * Copyright (c) 2003, 2007, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

package sun.jvm.hotspot.utilities.soql;

import java.util.*;
import sun.jvm.hotspot.oops.*;
import sun.jvm.hotspot.memory.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.utilities.*;

/**
 * This is SOQL (Simple Object Query Language) engine. This
 * uses JavaScript engine for the "select" and "where" expression
 * parts.
 */
public class SOQLEngine extends JSJavaScriptEngine {
   public static synchronized SOQLEngine getEngine() {
      if (soleInstance == null) {
         soleInstance = new SOQLEngine();
      }
      return soleInstance;
   }

   /**
      Query is of the form

         select <java script code to select>
         [ from [instanceof] <class name> [<identifier>]
           [ where <java script boolean expression> ]
         ]
   */
   public synchronized void executeQuery(String query, ObjectVisitor visitor)
                                                 throws SOQLException {
      debugPrint("query : " + query);
      StringTokenizer st = new StringTokenizer(query);
      if (st.hasMoreTokens()) {
         String first = st.nextToken();
         if (! first.equals("select") ) {
            throw new SOQLException("query syntax error: no 'select' clause");
         }
      } else {
         throw new SOQLException("query syntax error: no 'select' clause");
      }

      int selectStart = query.indexOf("select");
      int fromStart = query.indexOf("from");

      String selectExpr = null;
      String className = null;
      boolean isInstanceOf = false;
      String whereExpr = null;
      String identifier = null;

      if (fromStart != -1) {
         selectExpr = query.substring(selectStart + "select".length(), fromStart);
         st = new StringTokenizer(query.substring(fromStart + "from".length()));

         if (st.hasMoreTokens()) {
            String tmp = st.nextToken();
            if (tmp.equals("instanceof")) {
               isInstanceOf = true;
               if (! st.hasMoreTokens()) {
                  throw new SOQLException("no class name after 'instanceof'");
               }
               className = st.nextToken();
            } else {
               className = tmp;
            }
         } else {
            throw new SOQLException("query syntax error: class name must follow 'from'");
         }

         if (st.hasMoreTokens()) {
            identifier = st.nextToken();
            if (identifier.equals("where")) {
               throw new SOQLException("query syntax error: identifier should follow class name");
            }
            if (st.hasMoreTokens()) {
               String tmp = st.nextToken();
               if (! tmp.equals("where")) {
                  throw new SOQLException("query syntax error: 'where' clause expected after 'from' clause");
               }
               int whereEnd = query.lastIndexOf("where") + 5; // "where".length
               whereExpr = query.substring(whereEnd);
            }
         } else {
            throw new SOQLException("query syntax error: identifier should follow class name");
         }
      } else { // no from clause
         selectExpr = query.substring(selectStart + "select".length(), query.length());
      }

      executeQuery(new SOQLQuery(selectExpr, isInstanceOf, className, identifier, whereExpr), visitor);
   }

   private void executeQuery(SOQLQuery q, ObjectVisitor visitor) throws SOQLException {
      InstanceKlass kls = null;
      if (q.className != null) {
         kls = SystemDictionaryHelper.findInstanceKlass(q.className);
         if (kls == null) {
            throw new SOQLException(q.className + " is not found!");
         }
      }


      StringBuffer buf = new StringBuffer();
      buf.append("function result(");
      if (q.identifier != null) {
         buf.append(q.identifier);
      }
      buf.append(") { return ");
      buf.append(q.selectExpr.replace('\n', ' '));
      buf.append("; }");

      String selectCode = buf.toString();
      debugPrint(selectCode);
      String whereCode = null;
      if (q.whereExpr != null) {
         buf = new StringBuffer();
         buf.append("function filter(");
         buf.append(q.identifier);
         buf.append(") { return ");
         buf.append(q.whereExpr.replace('\n', ' '));
         buf.append("; }");
         whereCode = buf.toString();
         debugPrint(whereCode);
      } else {
         whereCode = "filter = null;";
      }

      beginQuery();
      // compile select expression and where condition
      evalString(selectCode, "", 1);
      evalString(whereCode,  "", 1);

      // iterate thru heap, if needed
      if (q.className != null) {
         try {
            iterateOops(kls, visitor, q.isInstanceOf);
         } finally {
            endQuery();
         }
      } else {
         // simple "select <expr>" query
         try {
            Object select = call("result", new Object[] {});
            visitor.visit(select);
         } catch (Exception e) {
            e.printStackTrace();
         }
      }
   }

   private void dispatchObject(Oop oop, ObjectVisitor visitor, boolean filterExists) {
      JSJavaObject jsObj = factory.newJSJavaObject(oop);
      Object[] args = new Object[] { jsObj };
      boolean b = true;

      try {
         if (filterExists) {
            Object res = call("filter", args);
            if (res instanceof Boolean) {
               b = ((Boolean)res).booleanValue();
            } else if (res instanceof Number) {
               b = ((Number)res).intValue() != 0;
            } else {
               b = (res != null);
            }
         }

         if (b) {
            Object select = call("result", args);
            visitor.visit(select);
         }
      } catch (Exception e) {
         throw new RuntimeException(e);
      }
   }

   private void iterateOops(final InstanceKlass ik, final ObjectVisitor visitor,
                            boolean includeSubtypes) {
      ObjectHeap oh = VM.getVM().getObjectHeap();
      oh.iterateObjectsOfKlass(new HeapVisitor() {
                    boolean filterExists;
                    public void prologue(long usedSize) {
                        filterExists = getScriptEngine().get("filter") != null;
                    }
                    public boolean doObj(Oop obj) {
                       dispatchObject(obj, visitor, filterExists);
                       return false;
                    }
                    public void epilogue() {}
                 }, ik, includeSubtypes);
   }

   // we create fresh ObjectReader and factory to avoid
   // excessive cache across queries.
   private void beginQuery() {
      objReader = new ObjectReader();
      factory = new JSJavaFactoryImpl();
   }

   // at the end of query we clear object reader cache
   // and factory cache
   private void endQuery() {
      objReader = null;
      factory = null;
   }

   protected ObjectReader getObjectReader() {
      return objReader;
   }

   protected JSJavaFactory getJSJavaFactory() {
      return factory;
   }

   protected boolean isQuitting() {
      return false;
   }

   protected void quit() {
      // do nothing
   }

   private static void debugPrint(String msg) {
      if (debug) System.out.println(msg);
   }

   private static final boolean debug;
   static {
      debug = System.getProperty("sun.jvm.hotspot.utilities.soql.SOQLEngine.debug") != null;
   }

   protected SOQLEngine() {
       super(debug);
       start();
   }

   private ObjectReader objReader;
   private JSJavaFactory factory;
   private static SOQLEngine soleInstance;
}

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