如何以编程方式评估托管bean中的EL [英] How to programmatically evaluate EL in a managed bean

问题描述

我想在基于Seam/JSF的应用程序中添加一种简单的模板语言，以使用户编写自己的电子邮件.

I would like to add a simple template language to my application based on Seam / JSF to let the users compose their own email.

由于我不想创建新的解析器，因此我想使用统一表达式语言自行设置上下文.

Since I don't want to create a new parser, I would like to use the Unified Expression Language setting the context all by myself.

我该怎么做?

推荐答案

如果您坐在JSF上下文中，则只需使用

If you're sitting inside the JSF context, then just use Application#evaluateExpressionGet() to programmatically evaluate a string containing EL expressions.

String unevaluatedString = convertMailTemplateToStringSomehow();
FacesContext context = FacesContext.getCurrentInstance();
String evaluatedString = context.getApplication().evaluateExpressionGet(context, unevaluatedString, String.class);
// ...

如果您不在JSF上下文中，则需要使用独立的EL API，例如 JUEL .或者，如果您已经使用EL 3.0，并且该字符串代表唯一的EL表达式，则使用

If you're not sitting inside the JSF context, then you'd need to use a standalone EL API, such as JUEL. Or, if you're already on EL 3.0 and the string represents the sole EL expression, then use the ELProcessor API.

ELProcessor el = new ELProcessor();
el.defineBean("bean", new Bean());
el.eval("bean.foo"); // Without starting #{ and ending } !
// ...

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