Thymeleaf扩展2(Say Hello)

这篇文章是“Thymeleaf扩展“的后续教程。 本文中的代码来自相同的示例应用程序,您可以从其GitHub仓库查看或下载该应用程序。

1. 对 hello 方言改进

到目前为止,HelloDialect允许将此变为:

<p hello:sayto="World">Hi ya!</p>

它工作得很好,但这里需要添加一些附加功能,作为学习演示。 例如:

  • 允许Spring EL表达式作为属性值,就像Spring Thymeleaf Dialect中的大多数标签一样。 例如:
    hello:sayto="${user.name}"
    

国际化输出:对英语说“Hello”,对西班牙语说“Hola”,对葡萄牙语说“Olá”等。
上面已经准备好了所有的工作,这里希望能够创建一个名为“saytoplanet”的新属性,并向太阳系中的所有行星问候,其模板如下:

<ul>
  <li th:each="planet : ${planets}" hello:saytoplanet="${planet}">Hello Planet!</li>
</ul>

它由一个Spring MVC控制器支持,该控制器包括所有这些行星作为一个叫作planets的模型属性:

@Controller
public class SayHelloController {

  public SayHelloController() {
    super();
  }

  @ModelAttribute("planets")
  public List<String> populatePlanets() {
    return Arrays.asList(new String[] {
        "Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"
    });
  }

  @RequestMapping({"/","/sayhello"})
  public String showSayHello() {
    return "sayhello";
  }

}

2. 为方言添加一个新的处理器

这里做的第一件事是添加一个新的处理器到现有的HelloDialect中。 为此,需要修改方言的getProcessors()方法,以包含新的SayToPlanetAttrProcessor类:

public class HelloDialect extends AbstractProcessorDialect {
  ...
  /*
   * Initialize the dialect's processors.
   *
   * Note the dialect prefix is passed here because, although we set
   * "hello" to be the dialect's prefix at the constructor, that only
   * works as a default, and at engine configuration time the user
   * might have chosen a different prefix to be used.
   */
  public Set<IProcessor> getProcessors(final String dialectPrefix) {
      final Set<IProcessor> processors = new HashSet<IProcessor>();
      processors.add(new SayToAttributeTagProcessor(dialectPrefix));
      processors.add(new SayToPlanetAttributeTagProcessor(dialectPrefix));
      return processors;
  }
  ...
}

3. 使用表达式作为属性值

现在想要在新处理器中添加解析和执行表达式的能力,就像在StandardSpringStandard方言中所做的那样,下面是Thymeleaf标准表达式:

  • ${...} - Spring EL变量表达式。
  • #{...} - 消息的外部化。
  • @{...} - 链接规范。
  • (cond)? (then) : (else) - 条件/默认表达式。

为了实现这一点,将使用标准表达式解析器,它将解析属性值为一个可执行的表达式对象:

public class SayToPlanetAttributeTagProcessor extends AbstractAttributeTagProcessor {

    private static final String ATTR_NAME = "saytoplanet";
    private static final int PRECEDENCE = 10000;

    private static final String SAYTO_PLANET_MESSAGE = "msg.helloplanet";

    public SayToPlanetAttributeTagProcessor(final String dialectPrefix) {
        super(
            TemplateMode.HTML, // This processor will apply only to HTML mode
            dialectPrefix,     // Prefix to be applied to name for matching
            null,              // No tag name: match any tag name
            false,             // No prefix to be applied to tag name
            ATTR_NAME,         // Name of the attribute that will be matched
            true,              // Apply dialect prefix to attribute name
            PRECEDENCE,        // Precedence (inside dialect's precedence)
            true);             // Remove the matched attribute afterwards
    }

    protected void doProcess(
            final ITemplateContext context, final IProcessableElementTag tag,
            final AttributeName attributeName, final String attributeValue,
            final IElementTagStructureHandler structureHandler) {

        /*
         * In order to evaluate the attribute value as a Thymeleaf Standard Expression,
         * we first obtain the parser, then use it for parsing the attribute value into
         * an expression object, and finally execute this expression object.
         */
        final IEngineConfiguration configuration = context.getConfiguration();

        final IStandardExpressionParser parser =
                StandardExpressions.getExpressionParser(configuration);

        final IStandardExpression expression = parser.parseExpression(context, attributeValue);

        final String planet = (String) expression.execute(context);
        /*
         * Set the salutation as the body of the tag, HTML-escaped and
         * non-processable (hence the 'false' argument)
         */
        structureHandler.setBody("Hello, planet " + planet, false);
    }
}

请注意,正如在前一篇文章中所做的,扩展AbstractAttributeTagProcessor抽象类。

4. 添加国际化

现在要将属性处理器返回的消息国际化。这意味着替换这个仅是英文的消息构建代码:

"Hello, planet " + planet;

从外部化的字符串构建的消息,x必须以某种方式从代码中获得。 上下文对象(ITemplateContext)提供需要的东西:

public String getMessage(
            final Class<?> origin, 
            final String key, 
            final Object[] messageParameters, 
            final boolean useAbsentMessageRepresentation);

它的参数有以下含义:

  • origin - 用于消息解析的起源类。 从处理器调用时,通常是处理器类本身。
  • key - 要检索的消息的键。
  • messageParameters - 要应用于请求的消息的参数。
  • origin - 在消息不存在或不存在的情况下是否应该返回缺少指定消息表示。

所以下面用它来实现一些国际化。 首先,需要一些.properties文件,如西班牙语的SayToPlanetAttributeTagProcessor_es.properties:

msg.helloplanet=¡Hola, planeta {0}!

葡萄牙语的SayToPlanetAttributeTagProcessor_pt.properties:

msg.helloplanet=Olá, planeta {0}!

等等,其它语言。

现在将不得不修改SayToPlanetAttributeTagProcessor处理器类来使用这些消息:

protected void doProcess(
        final ITemplateContext context, final IProcessableElementTag tag,
        final AttributeName attributeName, final String attributeValue,
        final IElementTagStructureHandler structureHandler) {

    /*
     * In order to evaluate the attribute value as a Thymeleaf Standard Expression,
     * we first obtain the parser, then use it for parsing the attribute value into
     * an expression object, and finally execute this expression object.
     */
    final IEngineConfiguration configuration = context.getConfiguration();

    final IStandardExpressionParser parser =
            StandardExpressions.getExpressionParser(configuration);

    final IStandardExpression expression = parser.parseExpression(context, attributeValue);

    final String planet = (String) expression.execute(context);

    /*
     * This 'getMessage(...)' method will first try to resolve the message
     * from the configured Spring Message Sources (because this is a Spring
     * -enabled application).
     * 
     * If not found, it will try to resolve it from a classpath-bound
     * .properties with the same name as the specified 'origin', which
     * in this case is this processor's class itself. This allows resources
     * to be packaged if needed in the same .jar files as the processors
     * they are used in.
     */
    final String i18nMessage =
            context.getMessage(
                    SayToPlanetAttributeTagProcessor.class,
                    SAYTO_PLANET_MESSAGE,
                    new Object[] {planet},
                    true);

    /*
     * Set the computed message as the body of the tag, HTML-escaped and
     * non-processable (hence the 'false' argument)
     */
    structureHandler.setBody(HtmlEscape.escapeHtml5(i18nMessage), false);

}protected void doProcess(
        final ITemplateContext context, final IProcessableElementTag tag,
        final AttributeName attributeName, final String attributeValue,
        final IElementTagStructureHandler structureHandler) {

    /*
     * In order to evaluate the attribute value as a Thymeleaf Standard Expression,
     * we first obtain the parser, then use it for parsing the attribute value into
     * an expression object, and finally execute this expression object.
     */
    final IEngineConfiguration configuration = context.getConfiguration();

    final IStandardExpressionParser parser =
            StandardExpressions.getExpressionParser(configuration);

    final IStandardExpression expression = parser.parseExpression(context, attributeValue);

    final String planet = (String) expression.execute(context);

    /*
     * This 'getMessage(...)' method will first try to resolve the message
     * from the configured Spring Message Sources (because this is a Spring
     * -enabled application).
     * 
     * If not found, it will try to resolve it from a classpath-bound
     * .properties with the same name as the specified 'origin', which
     * in this case is this processor's class itself. This allows resources
     * to be packaged if needed in the same .jar files as the processors
     * they are used in.
     */
    final String i18nMessage =
            context.getMessage(
                    SayToPlanetAttributeTagProcessor.class,
                    SAYTO_PLANET_MESSAGE,
                    new Object[] {planet},
                    true);

    /*
     * Set the computed message as the body of the tag, HTML-escaped and
     * non-processable (hence the 'false' argument)
     */
    structureHandler.setBody(HtmlEscape.escapeHtml5(i18nMessage), false);

}

接下来看看使用西班牙语区域设置执行模板的结果:

  • ¡Hola, planeta Mercury!
  • ¡Hola, planeta Venus!
  • ¡Hola, planeta Earth!
  • ¡Hola, planeta Mars!
  • ¡Hola, planeta Jupiter!
  • ¡Hola, planeta Saturn!
  • ¡Hola, planeta Uranus!
  • ¡Hola, planeta Neptune!

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