内置组件<t:errors>-优快云博客

本文详细解析了Tapestry5中Errors组件的工作原理，包括如何在表单中显示错误信息，参数配置如banner和class的作用，以及如何在实际项目中应用此组件。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

第一部分：源码

// Copyright 2006, 2007, 2008 The Apache Software Foundation
//
// 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.apache.tapestry5.corelib.components;

import org.apache.tapestry5.CSSClassConstants;
import org.apache.tapestry5.MarkupWriter;
import org.apache.tapestry5.ValidationTracker;
import org.apache.tapestry5.annotations.Environmental;
import org.apache.tapestry5.annotations.Parameter;
import org.apache.tapestry5.corelib.internal.InternalMessages;
import org.apache.tapestry5.services.FormSupport;

import java.util.List;

/**
 * Standard validation error presenter. Must be enclosed by a
 * {@link org.apache.tapestry5.corelib.components.Form} component. If errors are present, renders a
 * div element around a banner message and around an unnumbered list of
 * error messages. Renders nothing if the {@link org.apache.tapestry5.ValidationTracker} shows no
 * errors.
 */
public class Errors
{
    /**
     * The banner message displayed above the errors. The default value is "You must correct the
     * following errors before
     * you may continue.".
     */
    @Parameter("message:default-banner")
    private String banner;

    /**
     * The CSS class for the div element rendered by the component. The default value is "t-error".
     */
    @Parameter(name = "class")
    private String className = CSSClassConstants.ERROR;

    // Allow null so we can generate a better error message if missing
    @Environmental(false)
    private ValidationTracker tracker;

    void beginRender(MarkupWriter writer)
    {
        if (tracker == null)
            throw new RuntimeException(InternalMessages.encloseErrorsInForm());

        if (!tracker.getHasErrors())
            return;

        writer.element("div", "class", className);

        // Inner div for the banner text
        writer.element("div");
        writer.write(banner);
        writer.end();

        List<String> errors = tracker.getErrors();

        if (!errors.isEmpty())
        {
            // Only write out the <UL> if it will contain <LI> elements. An empty <UL> is not
            // valid XHTML.

            writer.element("ul");

            for (String message : errors)
            {
                writer.element("li");
                writer.write(message);
                writer.end();
            }

            writer.end(); // ul
        }

        writer.end(); // div

    }
}

第二部分：简介

<t:errors>主要用于在非客户端验证情况下的form错误信息显示。既然是非客户端验证情况下，就需要将<t:form>组件的clientValidation属性设置成false，否则你会看不到<t:errors>产生的ul标签。

该组件有两个参数：banner（用来指定错误列表的标题信息，默认是"You must correct the following errors before you may continue.".）和class（用来指定错误列表的CSS样式class名，默认是"t-error"）

第三部分：测试

以下是测试用的最终代码文件

start.tml

<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_0_0.xsd">
 <head>
  <title>t:errors</title>
  <style>
   .error{color:black;}  
  </style>
 </head>
    <body>
     <t:form clientValidation="false">
      <t:label for="userName"/>
         <t:textfield t:id="userName" validate="required" value="userName"/>
      <t:label for="password"/>
         <t:textfield t:id="password" validate="required" value="password"/>
         <input type="submit" value="Search"/>
         <t:errors/>
         <t:errors banner="literal:指定banner，未指定class"/>
         <t:errors banner="literal:同时指定banner和class" class="literal:error"/>
     </t:form>
    </body>
</html>

Start.java

package jumpstart.web.pages;

import org.apache.tapestry5.annotations.Property;

public class Start {
	@Property
	private String userName;
	@Property
	private String password;
}

最终的效果

最终测试效果

最终效果（HTML）

<form action="/jumpstart/start.form" method="post" id="form"><div class="t-invisible"><input value="BUFCDsKEovSgBAAA=" name="t:formdata" type="hidden"></input></div>
	    	<label class="t-error" for="userName">User Name</label>
	        <input class="t-error" value="" id="userName" name="userName" type="text"></input><img id="userName_icon" class="t-error-icon" alt="" src="/jumpstart/assets/de7155d829bf8977/core/spacer.gif"/>
	    	<label class="t-error" for="password">Password</label>
	        <input class="t-error" value="" id="password" name="password" type="text"></input><img id="password_icon" class="t-error-icon" alt="" src="/jumpstart/assets/de7155d829bf8977/core/spacer.gif"/>
	        <input value="Search" type="submit"></input>
	        <div class="t-error"><div>在你继续之前，必须纠正如下错误.</div><ul><li>请输入User Name的内容。</li><li>请输入Password的内容。</li></ul></div>
	        <div class="t-error"><div>指定banner，未指定class</div><ul><li>请输入User Name的内容。</li><li>请输入Password的内容。</li></ul></div>
	        <div class="error"><div>同时指定banner和class</div><ul><li>请输入User Name的内容。</li><li>请输入Password的内容。</li></ul></div>
	    </form>

第四部分：分析

源码中banner的参数指定的默认值使用了国际化message绑定表达式前缀，default-banner的值可以直接在组件所在包下的properties下找到。

源码中class的参数指定的默认值是CSSClassConstants.ERROR（常量值"t-error"）使用属性className保存，class只是指定的一个使用的别名。

源码中的beginRender方法主要知道tracker.getHasErrors()和tracker.getErrors()两句的作用就好了。

整个beginRender方法最后writer出来的结果就像上面图中所诠释的。

<div class="t-error">
    <div>指定banner，未指定class</div>
    <ul>
       <li>请输入User Name的内容。</li>
       <li>请输入Password的内容。</li>
    </ul>
</div>

根据这样的效果代码去理解源码就很好理解了。

转载于:https://my.oschina.net/namespace/blog/14887