Re: Substitute value in HashMap at runtime

mike <>
Fri, 14 Oct 2011 06:36:32 -0700 (PDT)
On Oct 13, 7:12 pm, Lew <> wrote:

Robert Klemme wrote:

mike wrote:

If I create a HashMap with something like:

static Map<String,String> map = new

If I do it like this I guess that MyPreferences.getVariableValue()
will not be substituted but be the "plain" string.

How can I make my MyPreferences.getVariableValue() be evaluated at
runtime? Any example?

One possible way is to change your Map to Map<String,
Callable<String>> and invoke call() at runtime.

Of course you then need to provide a proper implementation. :-)

Btw, does your Map contain more entries? If not, it's completely

If you define the Map as static you also need to be aware of
concurrency issues if your application will ever access this from
multiple threads.

It doesn't even have to be multiple threads. Multiple instances in the=

 same thread can clobber a static structure if careless. They just take =
turns messing each other up.



I put together a more complete example ( however it is not so small).
Here is the class ( see below).
The map will contain more values. Maybe I can do it final since it
will not change when values are loaded.

I will use the output from runtime value of

When I run the code below I get:

java.lang.NoSuchMethodException: test.TextHelp.getCurrentActivity()()
    at java.lang.Class.getMethod(
    at test.TextHelp.getValue(
    at test.TextHelp.replace(
    at test.TextHelp.main(

Any ideas?

I am using java 1.5 and cannot go with 1.6 yet.

Thanks for all your comments.


package test;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TextHelp {

    public String getCurrentActivity(){
        return "my activity name";

    public static void main (String [] args){
        TextHelp th = new TextHelp();
        System.out.println("Output before is: act-{stream}");
        String runtimeText = TextHelp.replace("act-{stream}");
        System.out.println("Output after is: "+runtimeText);

    private static Map<String, String> replacements = new HashMap<String,


    public static String replace(final String msg) {

        if (msg == null || "".equals(msg) || replacements == null
                || replacements.isEmpty()) {
            return msg;
        StringBuilder regexBuilder = new StringBuilder();
        Iterator<String> it = replacements.keySet().iterator();
        while (it.hasNext()) {
        Matcher matcher =
        StringBuffer out = new StringBuffer(msg.length() + (msg.length() /
        while (matcher.find()) {
            String toBeSubstituted = replacements.get(;
            String replacement = getValue(toBeSubstituted);
            matcher.appendReplacement(out, replacement);
        System.out.println("OUT "+out);
        return out.toString();

    public static String getValue(String expression) {

        String[] parts = expression.split(":");

        // Obtain the Class instance
        String result = "";
        try {
            // Obtain the Class
            // Obtain the Class instance
            Class cls = Class.forName(parts[0]);

            // Get the method
            Method method = cls.getMethod(parts[1],null);

            // Create the object that we want to invoke the methods on
            TextHelp provider = (TextHelp) cls
            // Call the method. Since none of them takes arguments we just
            // pass an empty array as second parameter.
            result = (String)method.invoke(provider, new Object[0]);

        } catch (IllegalArgumentException ex) {

        } catch (InvocationTargetException ex) {

        } catch (IllegalAccessException ex) {

        } catch (ClassNotFoundException ex) {

        } catch (SecurityException ex) {

        } catch (NoSuchMethodException ex) {
        } catch (InstantiationException ex) {
        System.out.println("Result " + ": " + result);
        return result;

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