Thymeleaf扩展2(Say Hello)
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小牛编辑
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2023-03-14
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Standard和SpringStandard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!