将简单的表达式语言放入java [英] Putting a simple expression language into java
问题描述
％artist％ - ％album％ - ％disctotal％
我的代码解析这些字段，并重新命名文件。但是我希望用户能够使用表达式，以便他们可以这样说：
$ if（％ disctotal％> = 01，％discno％）
使用 ifelse ，比较长度和大小写等等。
我不想从头开始写这个，有没有什么可以提供给我这个我可以只是插件对我的代码？
编辑：我认为Ive有一些很好的回复，但我的知识是让我失望。让我们简化问题我希望用户能写
$ if（％disctotal％> = 01，％discno％）
到gui中的一个字段。
然后在我的Java代码中，我希望能够将这个表达式应用于一组文件，所以对于每个文件，我有disctotal的价值，并且discno但我想要能够将表达式转换成像
if（discTotal> = 1）
{
return discNo
}
else
{
return
}
我不想做的是必须编写识别字符串的代码（
$ if（％disctotal％> = 01，％discno％）是一个if语句，因为这是要做的。
然后在此扩展，我希望表达式允许诸如大写字段之间的字段，检查字段的长度等。
另外：也许应该以这种方式工作，用户输入表达式，然后在稍后的日期为每个文件Java代码复制aces每个变量的实际值
ie
$ if（％disctotal％> = 01，％discno％） - > $ if（2> = 01 ，1）
然后将其传递给外部压缩语言进行解析并给出结果
这是Javascript的想法？
如何使用与Java 1.6捆绑在一起的JavaScript引擎？
您可以看到将传入所有参数：
ScriptEngineManager manager = new ScriptEngineManager（）;
ScriptEngine engine = manager.getEngineByName（JavaScript）;
engine.put（艺术家，艺术家）;
...
您将使用
$ b $读回该值b ScriptEngine.get（...）
胶水的最后一点是用函数声明来包围用户的表达式，并写一个调用函数的表达式，并将结果分配给一个众所周知的变量。
所以要开始实验，让我们有一个函数来测试表达式：
private static void printResult（final ScriptEngine jsEngine ，String name，String expr）throws ScriptException {
Object result = jsEngine.eval（expr）;
System.out.println（name +result：+ result +; expr：+ expr）;
}
现在我们来说：
public static void main（String [] args）throws Exception {
ScriptEngineManager sem = new ScriptEngineManager（）;
ScriptEngine jsEngine = sem.getEngineByName（JavaScript）;
printResult（jsEngine，Hello World，Hello World）;
printResult（jsEngine，Simple Math，123 + 456）;
}
这产生：
Hello World结果：Hello World; expr：'Hello World'
简单数学结果：579.0; expr：123 + 456
现在让我们尝试一下你的usecase：
public static void main（String [] args）throws Exception {
ScriptEngineManager sem = new ScriptEngineManager（）;
ScriptEngine jsEngine = sem.getEngineByName（JavaScript）;
String expr =artist +' - '+ album +（disktotal> 1？（'-D'+ diskno）：''）;
jsEngine.put（艺术家，U2）;
jsEngine.put（专辑，约书亚树）;
jsEngine.put（disktotal，1）;
jsEngine.put（diskno，1）;
printResult（jsEngine，Single Disk，expr）;
jsEngine.put（艺术家，Tori Amos）;
jsEngine.put（album，To Venus and Back）;
jsEngine.put（disktotal，2）;
jsEngine.put（diskno，2）;
printResult（jsEngine，Muti-Disk，expr）;
}
产生结果：
单磁盘结果：U2-Joshua Tree; expr：...
多磁盘结果：Tori Amos-To Venus和Back-D2; expr：...
注意Tori的最后有D2。
Im my Java application, users can specify how to name their files from a series of metadata fields. i.e
%artist% - %album% - %disctotal%
My code then parses these fields and renames file accoringly. But I want the user to be able to use an 'expression languge' so they can say things like:
$if(%disctotal% >= 01,%discno%)
Use ifelse, compare length and case and so on.
I dont want to write this from scratch, is there something that offers me this that I can just plugin to my code?
EDIT:I think Ive had some good replies, but my knowledge is letting me down. Lets simplify the issue I want the user to be able to write
$if(%disctotal% >= 01,%discno%)
into a field in a gui.
Then later on in my Java code I want to be able to apply this expression to a set of files, so for each file I have the value of disctotal, and discno but I want to be able to convert the expression into something like
if(discTotal >=1) { return discNo } else { return "" }
What I dont want to do is have to write the code that recognises the string (" $if(%disctotal% >= 01,%discno%)" is an if statement because this is akward to do.
Then expanding on this I would like the expression to allow things such as capitalizing oof fields, checking lengths of fields and so on.
Alternatively: Perhaps it should work this way, the user enters the expression, then at a later date for each file the Java code replaces each variable with the real value
i.e $if(%disctotal% >= 01,%discno%) -> $if(2 >= 01,1)
then this is passed to the exopression language to parse and give a result,
Is this the Javascript idea ?
How about using the JavaScript engine that is bundled with Java 1.6?
You can see how you would pass in all the parameters:
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");
engine.put("artist", artist);
...
You would read back the value using
ScriptEngine.get(...)
The final bit of glue would be to surround the user's expression with a function declaration, and write an expression that calls the function and assigns the result to a well known variable.
So to start experimenting, lets have a function to test expressions out:
private static void printResult(final ScriptEngine jsEngine, String name, String expr) throws ScriptException {
Object result = jsEngine.eval(expr);
System.out.println(name + " result: " + result + "; expr: " + expr);
}
Now let's call it:
public static void main(String[] args) throws Exception {
ScriptEngineManager sem = new ScriptEngineManager();
ScriptEngine jsEngine = sem.getEngineByName("JavaScript");
printResult(jsEngine, "Hello World", "'Hello World'");
printResult(jsEngine, "Simple Math", "123 + 456");
}
This produces:
Hello World result: Hello World; expr: 'Hello World'
Simple Math result: 579.0; expr: 123 + 456
Now lets try with your usecase:
public static void main(String[] args) throws Exception {
ScriptEngineManager sem = new ScriptEngineManager();
ScriptEngine jsEngine = sem.getEngineByName("JavaScript");
String expr = "artist + '-' + album + (disktotal > 1 ? ('-D' + diskno) : '')";
jsEngine.put("artist", "U2");
jsEngine.put("album", "The Joshua Tree");
jsEngine.put("disktotal", 1);
jsEngine.put("diskno", 1);
printResult(jsEngine, "Single Disk", expr);
jsEngine.put("artist", "Tori Amos");
jsEngine.put("album", "To Venus and Back");
jsEngine.put("disktotal", 2);
jsEngine.put("diskno", 2);
printResult(jsEngine, "Muti-Disk", expr);
}
Produces result:
Single Disk result: U2-The Joshua Tree; expr: ...
Muti-Disk result: Tori Amos-To Venus and Back-D2; expr: ...
Notice how Tori's has 'D2' at the end.
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