org.soulwing.cas.filter.FilterToBeanProxy.java Source code

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Here is the source code for org.soulwing.cas.filter.FilterToBeanProxy.java

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/*
 * FilterToBeanProxy.java
 *
 * Created on Feb 21, 2007
 *
 * Copyright (C) 2006, 2007 Carl E Harris, Jr.
 * 
 * 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.
 */
package org.soulwing.cas.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

/**
 * A Filter that acts as a proxy for a Spring bean.  The idea for this
 * filter is due to the authors of the Acegi Security framework.
 *
 * @author Carl Harris
 */
public class FilterToBeanProxy implements Filter {

    private static final String BEAN_NOT_FOUND = " not found in application context";

    private static final String MUST_IMPLEMENT_FILTER = " must implement Filter";

    private static final String INIT_PARAMETER_REQUIRED = " init parameter is required";

    private static final String TARGET_BEAN = "targetBean";

    private Filter target;

    /* 
     * @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
     */
    public void init(FilterConfig filterConfig) throws ServletException {
        target = getTargetBean(
                WebApplicationContextUtils.getRequiredWebApplicationContext(filterConfig.getServletContext()),
                getTargetBeanName(filterConfig));
    }

    /* 
     * @see javax.servlet.Filter#destroy()
     */
    public void destroy() {
        // not needed
    }

    /* 
     * @see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws IOException, ServletException {
        target.doFilter(request, response, filterChain);
    }

    private Filter getTargetBean(ApplicationContext appContext, String beanName) throws ServletException {
        if (appContext.containsBean(beanName)) {
            Object bean = appContext.getBean(beanName);
            if (bean instanceof Filter) {
                return (Filter) bean;
            } else {
                throw new ServletException(bean.getClass().getCanonicalName() + MUST_IMPLEMENT_FILTER);
            }
        } else {
            throw new ServletException(beanName + BEAN_NOT_FOUND);
        }
    }

    private String getTargetBeanName(FilterConfig filterConfig) throws ServletException {
        String beanName = filterConfig.getInitParameter(TARGET_BEAN);
        if (beanName == null) {
            throw new ServletException(TARGET_BEAN + INIT_PARAMETER_REQUIRED);
        }
        return beanName;
    }

}