Java Tutorial/Reflection/Package

Demonstrate Package

   <source lang="java">

class PkgTest {

 public static void main(String args[]) {
   Package pkgs[];
  
   pkgs = Package.getPackages();
  
   for(int i=0; i < pkgs.length; i++)
     System.out.println(
            pkgs[i].getName() + " " +
            pkgs[i].getImplementationTitle() + " " +
            pkgs[i].getImplementationVendor() + " " +
            pkgs[i].getImplementationVersion()
     );
  
 }

}</source>

Detect if a package is available

   <source lang="java">

public class Main{

 public static void  main(String args[]) {
   System.out.println(isAvailable("javax.swing.JComponent"));
 }
 public static boolean isAvailable(String className) {
   boolean isFound = false;
   try {
      Class.forName(className, false, null);
      isFound = true;
   }
   catch (ClassNotFoundException e) {
      isFound = false;
   }
   return isFound;
 }

}</source>

Find the Package of an Object

   <source lang="java">

import java.util.ArrayList; import java.util.Vector; public class Main {

 public static void main(String[] args) {
   System.out.println(new Vector().getClass().getPackage().getName());
   System.out.println(new ArrayList().getClass().getPackage().getName());
   System.out.println("Test String".getClass().getPackage().getName());
   System.out.println(new Integer(1).getClass().getPackage().getName());
 }

} /* java.util java.util java.lang java.lang

• /</source>

Get full package name

   <source lang="java">

public class Main {

 public static String getPackageName(Class c) {
   String fullyQualifiedName = c.getName();
   int lastDot = fullyQualifiedName.lastIndexOf(".");
   if (lastDot == -1) {
     return "";
   }
   return fullyQualifiedName.substring(0, lastDot);
 }
 public static void main(String[] args) {
   System.out.println(getPackageName(java.awt.Frame.class));
 }

}</source>

Get non Package Qualified Name

   <source lang="java">

public class Utils {

 public static String nonPackageQualifiedName( final Class<?> clazz ) {
     String name = clazz.getName();
     return name.substring(name.lastIndexOf(".") + 1);
 }

}</source>

Get package name of a class

   <source lang="java">

import java.util.Date; public class Main {

 public static void main(String[] args) {
   Date date = new Date();
   Package pack = date.getClass().getPackage();
   String packageName = pack.getName();
   System.out.println("Package Name = " + packageName);
 }

}</source>

Get Package Names From Dir

   <source lang="java">

/**

* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/

import java.io.File; import java.util.List; public final class ReflectionUtil {

 private static void getPackageNamesFromDir(File base, File dir, List<String> pkgs) {
   boolean foundClass = false;
   for (File file : dir.listFiles()) {
     if (file.isDirectory()) {
       getPackageNamesFromDir(base, file, pkgs);
     } else if (!foundClass && file.getName().endsWith(".class")) {
       foundClass = true;
       String pkg = "";
       file = dir;
       while (!file.equals(base)) {
         if (!"".equals(pkg)) {
           pkg = "." + pkg;
         }
         pkg = file.getName() + pkg;
         file = file.getParentFile();
       }
       if (!pkgs.contains(pkg)) {
         pkgs.add(pkg);
       }
     }
   }
 }
 private static String getPackageName(String clzName) {
   if (clzName.indexOf("/") == -1) {
     return null;
   }
   String packageName = clzName.substring(0, clzName.lastIndexOf("/"));
   return packageName.replace("/", ".");
 }

}</source>

getPackage() returns null for a class in the unnamed package

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class cls = MyClass.class;
   Package pkg = cls.getPackage(); // null
 }

} class MyClass{}</source>

getPackage() returns null for a primitive type or array

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Package pkg = int.class.getPackage(); // null
   pkg = int[].class.getPackage(); // null
 }

}</source>

Get the class name with or without the package

   <source lang="java">

public class Main {

 public static String getClassName(Class c) {
   String className = c.getName();
   int firstChar;
   firstChar = className.lastIndexOf(".") + 1;
   if (firstChar > 0) {
     className = className.substring(firstChar);
   }
   return className;
 }

 public static void main(String[] args) {
   System.out.println(getClassName(java.awt.Frame.class));
 }

}</source>

Get the package name of the specified class.

   <source lang="java">

import java.lang.reflect.Method; import java.net.URL; import java.security.CodeSource; import java.security.ProtectionDomain; import java.util.HashSet; import java.util.List; import java.util.Set; /*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This 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 software 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 software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

public class Main {

 /** The string used to separator packages */
 public static final String PACKAGE_SEPARATOR = ".";
 /**
  * Get the package name of the specified class.
  * 
  * @param classname
  *          Class name.
  * @return Package name or "" if the classname is in the default
  *         package.
  * 
  * @throws EmptyStringException
  *           Classname is an empty string.
  */
 public static String getPackageName(final String classname) {
   if (classname.length() == 0)
     System.out.println("Empty String Exception");
   int index = classname.lastIndexOf(PACKAGE_SEPARATOR);
   if (index != -1)
     return classname.substring(0, index);
   return "";
 }

}</source>

Get the short name of the specified class by striping off the package name.

   <source lang="java">

import java.lang.reflect.Method; import java.net.URL; import java.security.CodeSource; import java.security.ProtectionDomain; import java.util.HashSet; import java.util.List; import java.util.Set; /*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This 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 software 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 software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

public class Main {

 /** The string used to separator packages */
 public static final String PACKAGE_SEPARATOR = ".";
 /**
  * Get the short name of the specified class by striping off the package name.
  * 
  * @param classname
  *          Class name.
  * @return Short class name.
  */
 public static String stripPackageName(final String classname) {
   int idx = classname.lastIndexOf(PACKAGE_SEPARATOR);
   if (idx != -1)
     return classname.substring(idx + 1, classname.length());
   return classname;
 }

}</source>

Returns the package portion of the specified class

   <source lang="java">

public class Utils {

 /**
  * Returns the package portion of the specified class
  * @param className the name of the class from which to extract the package
  * @return package portion of the specified class
  */
 public static String getPackageName(final String className) {
     if (className != null) {
         final int index = className.lastIndexOf(".");
         return ((index != -1) ? className.substring(0, index) : ""); // NOI18N
     }
     return null;
 }

}</source>