RequestToViewNameTranslator可以在处理器返回的View为空时使用它根据Request获取viewName。RequestToViewNameTranslator提供的实现类只有一个DefaultRequestToViewNameTranslator。

接口RequestToViewNameTranslator中定义的如下：提供了getViewName抽象方法，其实就是根据request请求获取来组装视图名称。

public interface RequestToViewNameTranslator {

	/**
	 * Translate the given {@link HttpServletRequest} into a view name.
	 * @param request the incoming {@link HttpServletRequest} providing
	 * the context from which a view name is to be resolved
	 * @return the view name (or {@code null} if no default found)
	 * @throws Exception if view name translation fails
	 */
	String getViewName(HttpServletRequest request) throws Exception;

}

其实现类DefaultRequestToViewNameTranslator中的实现如下：其实其简单实现就是将请求名称作为视图名称返回，逻辑还是比较简单的。

@Override
	public String getViewName(HttpServletRequest request) {
		String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
		return (this.prefix + transformPath(lookupPath) + this.suffix);
	}

接下来我们看看RequestToViewNameTranslator在springMVC中的具体运行流程：

首先在DispatcherServlet的doDispatch函数中会设置默认的视图名

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		......
		//设置默认的视图名称
		applyDefaultViewName(processedRequest, mv);
		......
	}

在applyDefaultViewName中会判断ModelAndView的hasView为空时，就设置viewName

private void applyDefaultViewName(HttpServletRequest request, ModelAndView mv) throws Exception {
		if (mv != null && !mv.hasView()) {
			mv.setViewName(getDefaultViewName(request));
		}
	}

getDefaultViewName的实现逻辑还是在ViewNameTranslator中。

protected String getDefaultViewName(HttpServletRequest request) throws Exception {
		return this.viewNameTranslator.getViewName(request);
	}

在DefaultViewNameTranslator中实现的getViewName的逻辑如下，其实就是将请求路径作为ViewName

@Override
	public String getViewName(HttpServletRequest request) {
		String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
		return (this.prefix + transformPath(lookupPath) + this.suffix);
	}

实现类DefaultViewNameTranslator的完整源码如下：

public class DefaultRequestToViewNameTranslator implements RequestToViewNameTranslator {

	private static final String SLASH = "/";

	private String prefix = "";

	private String suffix = "";

	private String separator = SLASH;

	private boolean stripLeadingSlash = true;

	private boolean stripTrailingSlash = true;

	private boolean stripExtension = true;

	private UrlPathHelper urlPathHelper = new UrlPathHelper();

	public void setPrefix(String prefix) {
		this.prefix = (prefix != null ? prefix : "");
	}

	public void setSuffix(String suffix) {
		this.suffix = (suffix != null ? suffix : "");
	}

	public void setSeparator(String separator) {
		this.separator = separator;
	}

	public void setStripLeadingSlash(boolean stripLeadingSlash) {
		this.stripLeadingSlash = stripLeadingSlash;
	}

	public void setStripTrailingSlash(boolean stripTrailingSlash) {
		this.stripTrailingSlash = stripTrailingSlash;
	}

	public void setStripExtension(boolean stripExtension) {
		this.stripExtension = stripExtension;
	}

	public void setAlwaysUseFullPath(boolean alwaysUseFullPath) {
		this.urlPathHelper.setAlwaysUseFullPath(alwaysUseFullPath);
	}

	public void setUrlDecode(boolean urlDecode) {
		this.urlPathHelper.setUrlDecode(urlDecode);
	}

	public void setRemoveSemicolonContent(boolean removeSemicolonContent) {
		this.urlPathHelper.setRemoveSemicolonContent(removeSemicolonContent);
	}

	public void setUrlPathHelper(UrlPathHelper urlPathHelper) {
		Assert.notNull(urlPathHelper, "UrlPathHelper must not be null");
		this.urlPathHelper = urlPathHelper;
	}

	//根据请求获取视图名称
	@Override
	public String getViewName(HttpServletRequest request) {
		String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
		return (this.prefix + transformPath(lookupPath) + this.suffix);
	}

	protected String transformPath(String lookupPath) {
		String path = lookupPath;
		if (this.stripLeadingSlash && path.startsWith(SLASH)) {
			path = path.substring(1);
		}
		if (this.stripTrailingSlash && path.endsWith(SLASH)) {
			path = path.substring(0, path.length() - 1);
		}
		if (this.stripExtension) {
			path = StringUtils.stripFilenameExtension(path);
		}
		if (!SLASH.equals(this.separator)) {
			path = StringUtils.replace(path, SLASH, this.separator);
		}
		return path;
	}

}