Springmvc ViewResolver设计实现过程解析

总结：

viewresolver 如果要改需要自己注入到容器中并进行修改， springmvc使用的是interresourceviewresover
view不需要自己改，是springmvc根据return返回值选的

既然看到有modelandview直接跳转jsp的， 有请求转发的，有重定向的，这里整体是怎么设计的： (@responsebody的在此不作展开)

hicontroller:

@controller
public class hicontroller {
  @requestmapping("/hi")
  public modelandview gethi() {
    modelandview mav = new modelandview("me");
    return mav;
  }

  @requestmapping("/yes")
  public string forwardyes() {
    return "forward:patch";
  }

  @requestmapping("/no")
  public string redirectno() {
    return "redirect:patch";
  }

  @responsebody
  @requestmapping("/patch")
  public string redirectno() {
    return "from forward or redirect request";   // 这种情况没有view，在这里不讨论
  }
}

主要代码：

dispatcherservlet.dodispatch(）里的：

dispatcherservlet.render方法：

protected void render(modelandview mv, httpservletrequest request, httpservletresponse response) throws exception {
    // determine locale for request and apply it to the response.
    locale locale =
        (this.localeresolver != null ? this.localeresolver.resolvelocale(request) : request.getlocale());
    response.setlocale(locale);

    view view;
    string viewname = mv.getviewname();
    if (viewname != null) {
      // we need to resolve the view name.
      view = resolveviewname(viewname, mv.getmodelinternal(), locale, request);   // 1
      if (view == null) {
        throw new servletexception("could not resolve view with name '" + mv.getviewname() +
            "' in servlet with name '" + getservletname() + "'");
      }
    }
    else {
      // no need to lookup: the modelandview object contains the actual view object.
      view = mv.getview();
      if (view == null) {
        throw new servletexception("modelandview [" + mv + "] neither contains a view name nor a " +
            "view object in servlet with name '" + getservletname() + "'");
      }
    }

    // delegate to the view object for rendering.
    if (logger.istraceenabled()) {
      logger.trace("rendering view [" + view + "] ");
    }
    try {
      if (mv.getstatus() != null) {
        response.setstatus(mv.getstatus().value());
      }
      view.render(mv.getmodelinternal(), request, response);  // 2
    }
    catch (exception ex) {
      if (logger.isdebugenabled()) {
        logger.debug("error rendering view [" + view + "]", ex);
      }
      throw ex;
    }
  }

1. view = resolveviewname()会根据不同的路径生成不同的view, return mav 会返回jstlview, return "forward:/patch" 会返回internalresourceview， return "direct:/patch" 会返回indirectview

2. 不同的view去走不同的view.render()， 根据不同的view重写abstract void rendermergedoutputmodel方法

再来看是如何生成不同的view:[/code][code]view = resolveviewname() 进去，走到
diapatcherservlet先有viewresolver这个，用来生成不同的view

protected view resolveviewname(string viewname, @nullable map<string, object> model,
      locale locale, httpservletrequest request) throws exception {

    if (this.viewresolvers != null) {
      for (viewresolver viewresolver : this.viewresolvers) {
        view view = viewresolver.resolveviewname(viewname, locale);
        if (view != null) {
          return view;
        }
      }
    }
    return null;
  }

viewresolver 接口只有一个方法

public interface viewresolver {
  @nullable
  view resolveviewname(string viewname, locale locale) throws exception;

}

要配置具体的视图解析器，springmvc中使用的是interresourceviewresover，interresourceviewresover 和他的父类urlbasedviewresolver中都没有重写resolveviewname方法，再上一层的父类abstractcahingviewresolver实现了resolveviewname方法

abstractcahingviewresolver：

@override
  @nullable
  public view resolveviewname(string viewname, locale locale) throws exception {
    if (!iscache()) {
      return createview(viewname, locale);
    }
    else {
      object cachekey = getcachekey(viewname, locale);
      view view = this.viewaccesscache.get(cachekey);
      if (view == null) {
        synchronized (this.viewcreationcache) {
          view = this.viewcreationcache.get(cachekey);
          if (view == null) {
            // ask the subclass to create the view object.
            view = createview(viewname, locale);
            if (view == null && this.cacheunresolved) {
              view = unresolved_view;
            }
            if (view != null && this.cachefilter.filter(view, viewname, locale)) {
              this.viewaccesscache.put(cachekey, view);
              this.viewcreationcache.put(cachekey, view);
            }
          }
        }
      }
      else {
        if (logger.istraceenabled()) {
          logger.trace(formatkey(cachekey) + "served from cache");
        }
      }
      return (view != unresolved_view ? view : null);
    }
  }

interresourceviewresover中没有createview方法，所以是调用它父类urlbasedviewresolver的createview方法：

@override
  protected view createview(string viewname, locale locale) throws exception {
    // if this resolver is not supposed to handle the given view,
    // return null to pass on to the next resolver in the chain.
    if (!canhandle(viewname, locale)) {
      return null;
    }

    // check for special "redirect:" prefix.
    if (viewname.startswith(redirect_url_prefix)) {
      string redirecturl = viewname.substring(redirect_url_prefix.length());
      redirectview view = new redirectview(redirecturl,
          isredirectcontextrelative(), isredirecthttp10compatible());
      string[] hosts = getredirecthosts();
      if (hosts != null) {
        view.sethosts(hosts);
      }
      return applylifecyclemethods(redirect_url_prefix, view);  // return "direct:/patch"在这里构造view
    }

    // check for special "forward:" prefix.
    if (viewname.startswith(forward_url_prefix)) {
      string forwardurl = viewname.substring(forward_url_prefix.length());
      internalresourceview view = new internalresourceview(forwardurl);
      return applylifecyclemethods(forward_url_prefix, view);   // return "forward:/patch" 在这里构造view
    } 

    // else fall back to superclass implementation: calling loadview.
    return super.createview(viewname, locale);          // return mav 在这里构造view
  }

关于viewresolver的代码执行顺序， 前面分析那么多，这里再打断点快速验证一下：

进dispatcherservlet的dodispatch看到就是这个解析器：

断点放在这里，

然后下一步：

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。