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

古城微笑少年丶 2022-12-25 11:51 151阅读 0赞

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