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Struts example source code file (Scope.java)

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

Java - Struts tags/keywords

callable, class, exception, internalcontext, internalfactory, internalfactory, override, override, runtimeexception, strategy, string, string, t, t, threading, threads

The Struts Scope.java source code

/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed 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.
 */

package com.opensymphony.xwork2.inject;

import java.util.concurrent.Callable;

/**
 * Scope of an injected objects.
 *
 * @author crazybob
 */
public enum Scope {

  /**
   * One instance per injection.
   */
  DEFAULT {
    @Override
            <T> InternalFactory scopeFactory(Class type, String name,
        InternalFactory<? extends T> factory) {
      return factory;
    }
  },

  /**
   * One instance per container.
   */
  SINGLETON {
    @Override
            <T> InternalFactory scopeFactory(Class type, String name,
        final InternalFactory<? extends T> factory) {
      return new InternalFactory<T>() {
        T instance;
        public T create(InternalContext context) {
          synchronized (context.getContainer()) {
            if (instance == null) {
              instance = factory.create(context);
            }
            return instance;
          }
        }

        @Override
        public String toString() {
          return factory.toString();
        }
      };
    }
  },

  /**
   * One instance per thread.
   *
   * <p>Note: if a thread local object strongly references its {@link
   * Container}, neither the {@code Container} nor the object will be
   * eligible for garbage collection, i.e. memory leak.
   */
  THREAD {
    @Override
            <T> InternalFactory scopeFactory(Class type, String name,
        final InternalFactory<? extends T> factory) {
      return new InternalFactory<T>() {
        final ThreadLocal<T> threadLocal = new ThreadLocal();
        public T create(final InternalContext context) {
          T t = threadLocal.get();
          if (t == null) {
            t = factory.create(context);
            threadLocal.set(t);
          }
          return t;
        }

        @Override
        public String toString() {
          return factory.toString();
        }
      };
    }
  },

  /**
   * One instance per request.
   */
  REQUEST {
    @Override
            <T> InternalFactory scopeFactory(final Class type,
        final String name, final InternalFactory<? extends T> factory) {
      return new InternalFactory<T>() {
        public T create(InternalContext context) {
          Strategy strategy = context.getScopeStrategy();
          try {
            return strategy.findInRequest(
                type, name, toCallable(context, factory));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }

        @Override
        public String toString() {
          return factory.toString();
        }
      };
    }
  },

  /**
   * One instance per session.
   */
  SESSION {
    @Override
            <T> InternalFactory scopeFactory(final Class type,
        final String name, final InternalFactory<? extends T> factory) {
      return new InternalFactory<T>() {
        public T create(InternalContext context) {
          Strategy strategy = context.getScopeStrategy();
          try {
            return strategy.findInSession(
                type, name, toCallable(context, factory));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }

        @Override
        public String toString() {
          return factory.toString();
        }
      };
    }
  },

  /**
   * One instance per wizard.
   */
  WIZARD {
    @Override
            <T> InternalFactory scopeFactory(final Class type,
        final String name, final InternalFactory<? extends T> factory) {
      return new InternalFactory<T>() {
        public T create(InternalContext context) {
          Strategy strategy = context.getScopeStrategy();
          try {
            return strategy.findInWizard(
                type, name, toCallable(context, factory));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }

        @Override
        public String toString() {
          return factory.toString();
        }
      };
    }
  };

  <T> Callable toCallable(final InternalContext context,
      final InternalFactory<? extends T> factory) {
    return new Callable<T>() {
      public T call() throws Exception {
        return factory.create(context);
      }
    };
  }

  /**
   * Wraps factory with scoping logic.
   */
  abstract <T> InternalFactory scopeFactory(
      Class<T> type, String name, InternalFactory factory);

  /**
   * Pluggable scoping strategy. Enables users to provide custom
   * implementations of request, session, and wizard scopes. Implement and
   * pass to {@link
   * Container#setScopeStrategy(com.opensymphony.xwork2.inject.Scope.Strategy)}.
   */
  public interface Strategy {

    /**
     * Finds an object for the given type and name in the request scope.
     * Creates a new object if necessary using the given factory.
     */
    <T> T findInRequest(Class type, String name,
        Callable<? extends T> factory) throws Exception;

    /**
     * Finds an object for the given type and name in the session scope.
     * Creates a new object if necessary using the given factory.
     */
    <T> T findInSession(Class type, String name,
        Callable<? extends T> factory) throws Exception;

    /**
     * Finds an object for the given type and name in the wizard scope.
     * Creates a new object if necessary using the given factory.
     */
    <T> T findInWizard(Class type, String name,
        Callable<? extends T> factory) throws Exception;
  }
}

Other Struts examples (source code examples)

Here is a short list of links related to this Struts Scope.java source code file:

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