非 JSP（独立）上下文中的 JSTL/JSP EL（表达式语言）

发布于 2024-07-04 12:44:24 字数 889 浏览 5 评论 0原文

谁能推荐一个框架，用于在独立应用程序中按照 JSP EL（表达式语言）进行模板化/格式化消息？

我希望能够实例化某种类型的对象，给它一个模板，为

Dear ${customer.firstName}. You order will be dispatched on ${order.estimatedDispatchDate}

它提供一个上下文，其中包括参数对象的值字典（在本例中是一个名为“Customer”的对象）例如，“customer”，以及一个名为“order”的 Order 类型的对象）。

我知道有很多模板框架 - 其中许多在 Web 应用程序上下文之外工作，但我不认为这是一个大的重量级模板框架。只是 Java 已经提供的基本消息格式功能的更好版本

例如，我可以通过使用模板（或他们所说的“模式”）使用 java.text.MessageFormat 来完成上述操作，并且

Dear {0}. You order will be dispatched on {1,date,EEE dd MMM yyyy}

我可以将其传递给对象数组，在我调用Java程序中

new Object[] { customer.getFirstName(), order.getEstimatedDispatchDate() };

但是，在这种用法中，代码和模式是紧密相连的。虽然我可以将模式放入资源属性文件中，但代码和模式需要了解彼此的详细信息。使用类似 EL 的系统，代码和模式之间的契约将处于更高的级别（例如，客户和订单，而不是 customer.firstName 和 order.estimatedDispatchDate），从而更容易更改结构、订单和内容的消息，无需更改任何代码。

原文

Can anyone recommend a framework for templating/formatting messages in a standalone application along the lines of the JSP EL (Expression Language)?

I would expect to be able to instantiate a an object of some sort, give it a template along the lines of

Dear ${customer.firstName}. You order will be dispatched on ${order.estimatedDispatchDate}

provide it with a context which would include a value dictionary of parameter objects (in this case an object of type Customer with a name 'customer', say, and an object of type Order with a name 'order').

I know there are many template frameworks out there - many of which work outside the web application context, but I do not see this as a big heavyweight templating framework. Just a better version of the basic Message Format functionality Java already provides

For example, I can accomplish the above with java.text.MessageFormat by using a template (or a 'pattern' as they call it) such as

Dear {0}. You order will be dispatched on {1,date,EEE dd MMM yyyy}

and I can pass it an Object array, in my calling Java program

new Object[] { customer.getFirstName(), order.getEstimatedDispatchDate() };

However, in this usage, the code and the pattern are intimately linked. While I could put the pattern in a resource properties file, the code and the pattern need to know intimate details about each other. With an EL-like system, the contract between the code and the pattern would be at a much higher level (e.g. customer and order, rather then customer.firstName and order.estimatedDispatchDate), making it easier to change the structure, order and contents of the message without changing any code.

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笙痞 2024-07-11 12:44:24

Freemarker 会完全满足您的需求。这是一个模板引擎，其语法与 JSP 非常相似：

http://freemarker.org/

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雨轻弹 2024-07-11 12:44:24

啊啊。而使用 MessageFormat，我可以

Dear {0}. Your order will be dispatched on {1,date,EEE dd MMM yyyy}

在参数 #1 是 Date 对象的情况下执行操作，并且它根据模式进行格式化，但在 EL 中没有等效项。

在 JSP 中，我可能会使用格式标记。在此独立示例中，在计算表达式之前，我必须在代码中将日期格式化为字符串。

AAh. Whereas with MessageFormat, I can do

Dear {0}. Your order will be dispatched on {1,date,EEE dd MMM yyyy}

where parameter #1 is a Date object and it gets formatted according to the pattern, there is no equivalent in EL.

In JSP, I would have used, perhaps, a format tag. In this standalone example, I am going to have to format the Date as a String in my code prior to evaluating the expression.

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于我来说 2024-07-11 12:44:24

Ed 提倡在 Java EE 之外使用 EL 本身的想法Burns 和在服务器端讨论。 Tomcats 实现在单独的 JAR 中提供，但我不知道它是否可以使用服务器之外。

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淡淡の花香 2024-07-11 12:44:24

我会选择 Spring 表达式语言：

http: //docs.spring.io/spring/docs/current/spring-framework-reference/html/expressions.html

一些演示其威力的示例（前两个来自文档）：

int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);

// weekday is a String, e.g. "Mon", time is an int, e.g. 1400 or 900
{"Thu", "Fri"}.contains(weekday) and time matches '\d{4}'

表达式也可以使用对象属性：

public class Data {
    private String name; // getter and setter omitted
}

Data data = new Data();
data.setName("John Doe");

ExpressionParser p = new SpelExpressionParser();
Expression e = p.parseExpression("name == 'John Doe'");
Boolean r = (Boolean) e.getValue(data); // will return true

e = p.parseExpression("Hello " + name + ", how are you ?");
String text = e.getValue(data, String.class); // text will be "Hello John Doe, how are you ?"

I would go for the Spring Expression language:

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/expressions.html

A few examples which demonstrate the power (the first two are from the documentation):

int year = (Integer) parser.parseExpression("Birthdate.Year + 1900").getValue(context);

String city = (String) parser.parseExpression("placeOfBirth.City").getValue(context);

// weekday is a String, e.g. "Mon", time is an int, e.g. 1400 or 900
{"Thu", "Fri"}.contains(weekday) and time matches '\d{4}'

Expressions can also use object properties:

public class Data {
    private String name; // getter and setter omitted
}

Data data = new Data();
data.setName("John Doe");

ExpressionParser p = new SpelExpressionParser();
Expression e = p.parseExpression("name == 'John Doe'");
Boolean r = (Boolean) e.getValue(data); // will return true

e = p.parseExpression("Hello " + name + ", how are you ?");
String text = e.getValue(data, String.class); // text will be "Hello John Doe, how are you ?"

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