RequestContextAwareTag 自定义标签解决 TagSupport 不能进行 spring 的 bean 注入问题

在进行自定义标签时，使用 TagSupport，不能进行 spring 的 bean 注入，当然，我们可以自己实现，但是 spring 框架不可能没有考虑到这一点，因此不使用 TagSupport，而使用 spring 框架提供的 RequestContextAwareTag，进行自定义标签的开发，RequestContextAwareTag 实际上继承了 TagSupport，对 TagSupport 进行了扩展，扩展后就可以通过 spring 的 RequestContext 获取 spring 的 bean

下面是 RequestContextAwareTag 的源码

里面引入了私有属性 RequestContext，实现了 doStartTag 方法，留出抽象方法 doStartTagInternal 让使用者实现

/*
 * Copyright 2002-2012 the original author or authors.
 *
 * 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 org.springframework.web.servlet.tags;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.tagext.TagSupport;
import javax.servlet.jsp.tagext.TryCatchFinally;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.web.servlet.support.JspAwareRequestContext;
import org.springframework.web.servlet.support.RequestContext;

/**
 * Superclass for all tags that require a {@link RequestContext}.
 *
 * <p>The {@code RequestContext} instance provides easy access
 * to current state like the
 * {@link org.springframework.web.context.WebApplicationContext},
 * the {@link java.util.Locale}, the
 * {@link org.springframework.ui.context.Theme}, etc.
 *
 * <p>Mainly intended for
 * {@link org.springframework.web.servlet.DispatcherServlet} requests;
 * will use fallbacks when used outside {@code DispatcherServlet}.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see org.springframework.web.servlet.support.RequestContext
 * @see org.springframework.web.servlet.DispatcherServlet
 */
@SuppressWarnings("serial")
public abstract class RequestContextAwareTag extends TagSupport implements TryCatchFinally {

	/**
	 * {@link javax.servlet.jsp.PageContext} attribute for the
	 * page-level {@link RequestContext} instance.
	 */
	public static final String REQUEST_CONTEXT_PAGE_ATTRIBUTE =
			"org.springframework.web.servlet.tags.REQUEST_CONTEXT";


	/** Logger available to subclasses */
	protected final Log logger = LogFactory.getLog(getClass());


	private RequestContext requestContext;


	/**
	 * Create and expose the current RequestContext.
	 * Delegates to {@link #doStartTagInternal()} for actual work.
	 * @see #REQUEST_CONTEXT_PAGE_ATTRIBUTE
	 * @see org.springframework.web.servlet.support.JspAwareRequestContext
	 */
	@Override
	public final int doStartTag() throws JspException {
		try {
			this.requestContext = (RequestContext) this.pageContext.getAttribute(REQUEST_CONTEXT_PAGE_ATTRIBUTE);
			if (this.requestContext == null) {
				this.requestContext = new JspAwareRequestContext(this.pageContext);
				this.pageContext.setAttribute(REQUEST_CONTEXT_PAGE_ATTRIBUTE, this.requestContext);
			}
			return doStartTagInternal();
		}
		catch (JspException ex) {
			logger.error(ex.getMessage(), ex);
			throw ex;
		}
		catch (RuntimeException ex) {
			logger.error(ex.getMessage(), ex);
			throw ex;
		}
		catch (Exception ex) {
			logger.error(ex.getMessage(), ex);
			throw new JspTagException(ex.getMessage());
		}
	}

	/**
	 * Return the current RequestContext.
	 */
	protected final RequestContext getRequestContext() {
		return this.requestContext;
	}

	/**
	 * Called by doStartTag to perform the actual work.
	 * @return same as TagSupport.doStartTag
	 * @throws Exception any exception, any checked one other than
	 * a JspException gets wrapped in a JspException by doStartTag
	 * @see javax.servlet.jsp.tagext.TagSupport#doStartTag
	 */
	protected abstract int doStartTagInternal() throws Exception;


	@Override
	public void doCatch(Throwable throwable) throws Throwable {
		throw throwable;
	}

	@Override
	public void doFinally() {
		this.requestContext = null;
	}

}

使用 RequestContextAwareTag 代替 TagSupport 实现 spring 的 bean 注入代码如下

package com.sala.config;

import com.sala.service.DepartmentService;
import org.springframework.web.servlet.tags.RequestContextAwareTag;
import javax.servlet.jsp.tagext.TagSupport;

public class UserTag extends RequestContextAwareTag {
    @Override
    protected int doStartTagInternal() throws Exception {
        //获取spring容器中的bean
        DepartmentService departmentService = this.getRequestContext().getWebApplicationContext().getBean(DepartmentService.class);
        
        return TagSupport.EVAL_BODY_INCLUDE;
    }
}

至此完

标签：自定义,RequestContext,spring,springframework,bean,ex,TagSupport,org,servlet
来源： https://blog.csdn.net/wsjzzcbq/article/details/110442542