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}.** 
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.** 
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*/@Overridepublic 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;@Overridepublic void doCatch(Throwable throwable) throws Throwable {throw throwable;}@Overridepublic 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 {@Overrideprotected int doStartTagInternal() throws Exception {//获取spring容器中的beanDepartmentService departmentService = this.getRequestContext().getWebApplicationContext().getBean(DepartmentService.class);return TagSupport.EVAL_BODY_INCLUDE;}
}

至此完

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