评价表达式在常规表达中的价值 [英] evaluating value of an expression as expression in groovy

问题描述

这里是我想要工作的代码

Here is the code i am trying to get working

    def expr = ''
    List params = []
    params << 'filter-name'
    params << 'servlet-name'
    params << 'url-pattern'

    params.each{expr = expr+ "it.'${it}'.text().trim()#"}
    expr = expr.substring(0, expr.length()-1)

    consNodes.each{
        println "data is:$"{expr}"
        println "actual : ${it.'filter-name'.text().trim()}#${it.'servlet-name'.text().trim()}#${it.'url-pattern'.text().trim()}"
}

就像

in the above result comes like

data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : presenceLogoutFilter##/adfAuthentication/*
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : remoteApplication##/rr/*
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : ServletADFContextFilter#GetHandler#
data is:it.'filter-name'.text().trim()#it.'servlet-name'.text().trim()#it.'url-pattern'.text().trim()
actual : ServletADFContextFilter##/PresenceServlet/*

因此，您可以看到我构建的表达式无法进一步评估。任何建议如何使它工作？

So, as you can see that my constructed expression is not able to evaluate further. Any advise on how to make it work?

推荐答案

问题是你正在创建一个 GString 像这样：it。'$ {it}'.text（）。trim（）＃，但是然后转换它当你连接它时，你可以将它放到一个 String 中： expr +it。'$ {it}'.text（）。trim（）＃ code>。一旦将 GString 变成字符串，它不再评估表达式。但即使你提到它不能解决你的问题，因为 GString 不像你认为的那样评估。解释它的最好方法是用一个例子：



The problem is that you're creating a GString like this: "it.'${it}'.text().trim()#", but then you're converting it into a String when you concatenate it: expr + "it.'${it}'.text().trim()#". Once you turn a GString into a String it no longer evaluates expressions. But even if you address that it won't solve your problem because GStrings do not evaluate like you think they do. The best way to explain it is with an example:

import org.codehaus.groovy.runtime.GStringImpl

// What you're doing
def a = 'John'
def b = 'Hello, $a'
def c = "${a}"

assert b == 'Hello, $a'

// What the compiler is doing (ignoring the variable name changes)
def aa = 'John'
def bb = 'Hello, $a'
def cc = new GStringImpl([] as Object[], ['Hello, $a'] as String[])

assert cc == 'Hello, $a'

// What you want the compiler to do, but it will not.
def aaa = 'John'
def bbb = 'Hello, $a'
def ccc = new GStringImpl(['John'] as Object[], ['Hello, '] as String[])

assert ccc == 'Hello, John'

如果你真的想要，你可以手动建立 GString s，但这会非常困难。并且最终取决于不保证在Groovy发行版之间保持向后兼容的类。

If you really want to, you can build the GStrings manually, but that will be very difficult. And you'd end up depending on a class which is not guaranteed to remain backward-compatible between Groovy releases.

以下是您可以做的事情：

Here's what you can do instead:

def params = []

params << 'filter-name'
params << 'servlet-name'
params << 'url-pattern'

def evaluators = params.collect { 
    { attr, node -> node[attr]?.text()?.trim() ?: '' }.curry(it)
}

consNodes.each { node ->
    println evaluators.collect { c -> c(node) }.join('#')    
}

输出看起来像这：

The output looks like this:

presenceLogoutFilter##/adfAuthentication/*
remoteApplication##/rr/*
ServletADFContextFilter#GetHandler#
ServletADFContextFilter##/PresenceServlet/*

并列出一系列闭包，每个负责评估节点属性。然后，您可以将结果加入'＃'。

Instead of a single large expression you and up with a list of closures, each responsible for evaluating a node attribute. Then, you can join the results with '#'s.

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