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executing java expression from a text file!

 
Mike Mass
Greenhorn
Posts: 12
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Hi all!

This might be far fetched, but i really need to know if its possible to read a java expression from a text file and execute it.
Example : width = imgwidth - 100;
Where the variables r defined and known by the class that read this line.

Thanks in advance!
 
Kai Witte
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hello,

that is possible. In the general case it is quite hard. For a simple construct like your example there is an easy way, however:
  • read the file as a properties file using java.util.Properties
  • get the property "width"
  • replace imgwidth by x using String#replaceAll
  • use jfunction to evaluate the resulting String: width=Terms.evaluate(resultingString, imgwidth);


  • Kai
     
    Michael Lloyd Lee
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    beanshell?
     
    Ulf Dittmer
    Rancher
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    There are a number of libraries that allow you to do that. Google for JEP or JEL. JEP builds an expression tree and interprets it using values, which makes it a bit slow. JEL compiles the expression, which is much faster, but can be tricky to handle to situations where you have multiple classloaders. For the ultimate Java integration, look for Javassist, which lets you build your own Java classes from Strings of code - very cool.
     
    Mike Mass
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    I would like ot thank each of you for your contribution, particularly Mr Dittmer. JEP is the answer to what i have in mind, since i will integrate it to an ant task, speed is not an issue.

    Thanks again guys,

    Mike
    [ September 08, 2005: Message edited by: Mike Mass ]
     
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