22_5 Spring MVC - ViewResolver系列 - InternalResourceViewResolver

22_5 Spring MVC - ViewResolver系列 - InternalResourceViewResolver

一、简介

InternalResourceViewResolver是URLBasedViewResolver的子类，所以URLBasedViewResolver支持的特性它都支持。在实际应用中InternalResourceViewResolver也是使用的最广泛的一个视图解析器。InternalResourceViewResolver会把返回的视图名称都解析为InternalResourceView对象，InternalResourceView会把Controller处理器方法返回的模型属性都存放到对应的request属性中，然后通过RequestDispatcher在服务器端把请求forword重定向到目标URL。

二、源码解析

package org.springframework.web.servlet.view;

import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;


public class InternalResourceViewResolver extends UrlBasedViewResolver {

	private static final boolean jstlPresent = ClassUtils.isPresent(
			"javax.servlet.jsp.jstl.core.Config", InternalResourceViewResolver.class.getClassLoader());

	@Nullable
	private Boolean alwaysInclude;


	/**
	 * Sets the default {@link #setViewClass view class} to {@link #requiredViewClass}:
	 * by default {@link InternalResourceView}, or {@link JstlView} if the JSTL API
	 * is present.
	 */
	public InternalResourceViewResolver() {
		Class<?> viewClass = requiredViewClass();
		if (InternalResourceView.class == viewClass && jstlPresent) {
			viewClass = JstlView.class;
		}
		setViewClass(viewClass);
	}

	/**
	 * A convenience constructor that allows for specifying {@link #setPrefix prefix}
	 * and {@link #setSuffix suffix} as constructor arguments.
	 * @param prefix the prefix that gets prepended to view names when building a URL
	 * @param suffix the suffix that gets appended to view names when building a URL
	 * @since 4.3
	 */
	public InternalResourceViewResolver(String prefix, String suffix) {
		this();
		setPrefix(prefix);
		setSuffix(suffix);
	}


	/**
	 * This resolver requires {@link InternalResourceView}.
	 */
	@Override
	protected Class<?> requiredViewClass() {
		return InternalResourceView.class;
	}

	/**
	 * Specify whether to always include the view rather than forward to it.
	 * <p>Default is "false". Switch this flag on to enforce the use of a
	 * Servlet include, even if a forward would be possible.
	 * @see InternalResourceView#setAlwaysInclude
	 */
	public void setAlwaysInclude(boolean alwaysInclude) {
		this.alwaysInclude = alwaysInclude;
	}


	@Override
	protected AbstractUrlBasedView buildView(String viewName) throws Exception {
		InternalResourceView view = (InternalResourceView) super.buildView(viewName);
		if (this.alwaysInclude != null) {
			view.setAlwaysInclude(this.alwaysInclude);
		}
		view.setPreventDispatchLoop(true);
		return view;
	}

}

InternalResourceViewResolver 的实现源码其实很少，如上所示。

• 它将InternalResourceView 作为默认的View类。
• InternalResourceViewResolver 无论能不能解析都不会返回null，也就是说它拦截了所有的逻辑视图，让后续的解析器得不到执行，所以InternalResourceViewResolver 解析器必须放在最后