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XWork is an command-pattern framework that is used to power WebWork as well as other applications. XWork provides an Inversion of Control container, a powerful expression language, data type conversion, validation, and pluggable configuration.
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/*
 * Copyright (c) 2002-2007 by OpenSymphony
 * All rights reserved.
 */
package com.opensymphony.xwork2.interceptor;

import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.Preparable;
import com.opensymphony.xwork2.util.logging.Logger;
import com.opensymphony.xwork2.util.logging.LoggerFactory;

import java.lang.reflect.InvocationTargetException;


/**
 * 
 *
 * This interceptor calls prepare() on actions which implement
 * {@link Preparable}. This interceptor is very useful for any situation where
 * you need to ensure some logic runs before the actual execute method runs.
 *
 *  A typical use of this is to run some logic to load an object from the
 * database so that when parameters are set they can be set on this object. For
 * example, suppose you have a User object with two properties: id and
 * name. Provided that the params interceptor is called twice (once
 * before and once after this interceptor), you can load the User object using
 * the id property, and then when the second params interceptor is called the
 * parameter user.name will be set, as desired, on the actual object
 * loaded from the database. See the example for more info.
 *
 * 

 * Note: Since XWork 2.0.2, this interceptor extends {@link MethodFilterInterceptor}, therefore being
 * able to deal with excludeMethods / includeMethods parameters. See [Workflow Interceptor]
 * (class {@link DefaultWorkflowInterceptor}) for documentation and examples on how to use this feature.
 *
 * 
Update: Added logic to execute a prepare{MethodName} and conditionally
 * the a general prepare() Method, depending on the 'alwaysInvokePrepare' parameter/property
 * which is by default true. This allows us to run some logic based on the method
 * name we specify in the {@link com.opensymphony.xwork2.ActionProxy}. For example, you can specify a
 * prepareInput() method that will be run before the invocation of the input method.
 *
 * 
 *
 * 
 Interceptor parameters:
 *
 * 
 *
 * 

 *
 * alwaysInvokePrepare - Default to true. If true, prepare will always be invoked,
 * otherwise it will not.
 *
 * 
 *
 * 
 *
 *  Extending the interceptor:
 *
 * 

 *
 * 
 *
 * There are no known extension points to this interceptor.
 *
 * 
 *
 * 
 Example code:
 *
 * 
 * 
 * <!-- Calls the params interceptor twice, allowing you to
 *       pre-load data for the second time parameters are set -->
 *  <action name="someAction" class="com.examples.SomeAction">
 *      <interceptor-ref name="params"/>
 *      <interceptor-ref name="prepare"/>
 *      <interceptor-ref name="basicStack"/>
 *      <result name="success">good_result.ftl</result>
 *  </action>
 * 
 * 
 *
 * @author Jason Carreira
 * @author Philip Luppens
 * @author tm_jee
 * @see com.opensymphony.xwork2.Preparable
 */
public class PrepareInterceptor extends MethodFilterInterceptor {

    private static final long serialVersionUID = -5216969014510719786L;

    private static final Logger LOG = LoggerFactory.getLogger(PrepareInterceptor.class);

    private final static String PREPARE_PREFIX = "prepare";
    private final static String ALT_PREPARE_PREFIX = "prepareDo";

    private boolean alwaysInvokePrepare = true;

    /**
     * Sets if the preapare method should always be executed.
     * 
     * Default is true.
     *
     * @param alwaysInvokePrepare if prepare should always be executed or not.
     */
    public void setAlwaysInvokePrepare(String alwaysInvokePrepare) {
        this.alwaysInvokePrepare = Boolean.parseBoolean(alwaysInvokePrepare);
    }

    @Override
    public String doIntercept(ActionInvocation invocation) throws Exception {
        Object action = invocation.getAction();

        if (action instanceof Preparable) {
            try {
                PrefixMethodInvocationUtil.invokePrefixMethod(invocation,
                        new String[]{PREPARE_PREFIX, ALT_PREPARE_PREFIX});
            }
            catch (InvocationTargetException e) {
                // just in case there's an exception while doing reflection,
                // we still want prepare() to be able to get called.
                LOG.warn("an exception occured while trying to execute prefixed method", e);
            }
            catch (IllegalAccessException e) {
                // just in case there's an exception while doing reflection,
                // we still want prepare() to be able to get called.
                LOG.warn("an exception occured while trying to execute prefixed method", e);
            } catch (Exception e) {
                // just in case there's an exception while doing reflection,
                // we still want prepare() to be able to get called.
                LOG.warn("an exception occured while trying to execute prefixed method", e);
            }

            if (alwaysInvokePrepare) {
                ((Preparable) action).prepare();
            }
        }

        return invocation.invoke();
    }

}