Substitute value in HashMap at runtime
 

Hi,

If I create a HashMap with something like:

static Map<String,String> map = new
HashMap<String,String>("variable",MyPreferences.ge tVariableValue());

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?

br,

//mike

Re: Substitute value in HashMap at runtime
 

mike wrote:
> If I create a HashMap with something like:
>
> static Map<String,String> map = new
> HashMap<String,String>("variable",MyPreferences.ge tVariableValue());
>
> If I do it like this I guess that MyPreferences.getVariableValue()
> will not be substituted but be the "plain" string.

Nope. If you do it like that your code will fail to compile (assuming you're referring to 'java.util.HashMap').
<http://download.oracle.com/javase/7/docs/api/java/util/HashMap.html>

Put together a Simple Self-Contained Compilable Example (SSCCE) per
http://sscce.org/

Seriously. Do it.

Even if you use a correct constructor, if 'MyPreferences.getVariableValue()' is not of type 'String' you have a problem:

public class Foo
{
static Map<String,String> map = new HashMap<>();
static
{
map.put( "variable", MyPreferences.getVariableValue() );
}
}

The type of the entry must match the type of the target.

BTW, I assume that 'getVariableValue()' is a static member of 'MyPreferences', given that you named the latter as a type and not a variable.

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

Use the expression 'MyPreferences.getVariableValue()'.

Let's see that SSCCE in your next post, otherwise there's not much point in continuing, is there? We need full data to understand what you aim to accomplish, and you need full data for any answer to make any sense.

SSCCE.

http://sscce.org/

--
Lew

Re: Substitute value in HashMap at runtime
 

On Oct 13, 2:18*pm, mike <mikaelpetter...@hotmail.com> wrote:
> If I create a HashMap with something like:
>
> static Map<String,String> map = new
> HashMap<String,String>("variable",MyPreferences.ge tVariableValue());
>
> 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.

http://download.oracle.com/javase/6/.../Callable.html

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

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

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.

Cheers

robert

Re: Substitute value in HashMap at runtime
 

Robert Klemme wrote:
> mike wrote:
>> If I create a HashMap with something like:
>>
>> static Map<String,String> map = new
>> HashMap<String,String>("variable",MyPreferences.ge tVariableValue());
>>
>> 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.
>
> http://download.oracle.com/javase/6/.../Callable.html
>
> Of course you then need to provide a proper implementation. :-)
>
> Btw, does your Map contain more entries? If not, it's completely
> superfluous.
>
> 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.

--
Lew

Re: Substitute value in HashMap at runtime
 

On Oct 13, 7:12*pm, Lew <lewbl...@gmail.com> wrote:
> Robert Klemme wrote:
> > mike wrote:
> >> If I create a HashMap with something like:
>
> >> static Map<String,String> map = new
> >> HashMap<String,String>("variable",MyPreferences.ge tVariableValue());
>
> >> 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.
>
> >http://download.oracle.com/javase/6/...concurrent/Cal...
>
> > Of course you then need to provide a proper implementation. :-)
>
> > Btw, does your Map contain more entries? *If not, it's completely
> > superfluous.
>
> > 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 thesame thread can clobber a static structure if careless. *They just take turns messing each other up.
>
> --
> Lew

Hi,

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
test.TextHelp.getCurrentActivity().

When I run the code below I get:

java.lang.NoSuchMethodException: test.TextHelp.getCurrentActivity()()
at java.lang.Class.getMethod(Class.java:1581)
at test.TextHelp.getValue(TextHelp.java:70)
at test.TextHelp.replace(TextHelp.java:47)
at test.TextHelp.main(TextHelp.java:21)

Any ideas?

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

Thanks for all your comments.

//mike

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,
String>();

static{
replacements.put("{stream}","test.TextHelp:getCurr entActivity()");
}

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();
regexBuilder.append(Pattern.quote(it.next()));
while (it.hasNext()) {
regexBuilder.append('|').append(Pattern.quote(it.n ext()));
}
Matcher matcher =
Pattern.compile(regexBuilder.toString()).matcher(m sg);
StringBuffer out = new StringBuffer(msg.length() + (msg.length() /
10));
while (matcher.find()) {
String toBeSubstituted = replacements.get(matcher.group());
String replacement = getValue(toBeSubstituted);
matcher.appendReplacement(out, replacement);
//matcher.appendReplacement(out,
replacements.get(matcher.group()));
}
matcher.appendTail(out);
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
.newInstance();
// 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) {
ex.printStackTrace();

} catch (InvocationTargetException ex) {
ex.printStackTrace();

} catch (IllegalAccessException ex) {
ex.printStackTrace();

} catch (ClassNotFoundException ex) {
ex.printStackTrace();

} catch (SecurityException ex) {
ex.printStackTrace();

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

Re: Substitute value in HashMap at runtime
 

On Oct 14, 3:36*pm, mike <mikaelpetter...@hotmail.com> wrote:
> On Oct 13, 7:12*pm, Lew <lewbl...@gmail.com> wrote:
>
>
>
>
>
>
>
>
>
> > Robert Klemme wrote:
> > > mike wrote:
> > >> If I create a HashMap with something like:
>
> > >> static Map<String,String> map = new
> > >> HashMap<String,String>("variable",MyPreferences.ge tVariableValue());
>
> > >> 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.
>
> > >http://download.oracle.com/javase/6/...concurrent/Cal....
>
> > > Of course you then need to provide a proper implementation. :-)
>
> > > Btw, does your Map contain more entries? *If not, it's completely
> > > superfluous.
>
> > > 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.
>
> > --
> > Lew
>
> Hi,
>
> 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
> test.TextHelp.getCurrentActivity().
>
> When I run the code below I get:
>
> java.lang.NoSuchMethodException: test.TextHelp.getCurrentActivity()()
> * * * * at java.lang.Class.getMethod(Class.java:1581)
> * * * * at test.TextHelp.getValue(TextHelp.java:70)
> * * * * at test.TextHelp.replace(TextHelp.java:47)
> * * * * at test.TextHelp.main(TextHelp.java:21)
>
> Any ideas?
>
> I am using java 1.5 and cannot go with 1.6 yet.
>
> Thanks for all your comments.
>
> //mike
>
> 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,
> String>();
>
> * * * * static{
> * * * * * * * * replacements.put("{stream}","test.TextHelp:getCurr entActivity()");
> * * * * }
>
> * * * * 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();
> * * * * * * * * regexBuilder.append(Pattern.quote(it.next()));
> * * * * * * * * while (it.hasNext()) {
> * * * * * * * * * * * * regexBuilder.append('|').append(Pattern.quote(it.n ext()));
> * * * * * * * * }
> * * * * * * * * Matcher matcher =
> Pattern.compile(regexBuilder.toString()).matcher(m sg);
> * * * * * * * * StringBuffer out = new StringBuffer(msg..length() + (msg.length() /
> 10));
> * * * * * * * * while (matcher.find()) {
> * * * * * * * * * * * * String toBeSubstituted = replacements.get(matcher.group());
> * * * * * * * * * * * * String replacement = getValue(toBeSubstituted);
> * * * * * * * * * * * * matcher.appendReplacement(out, replacement);
> * * * * * * * * * * * * //matcher.appendReplacement(out,
> replacements.get(matcher.group()));
> * * * * * * * * }
> * * * * * * * * matcher.appendTail(out);
> * * * * * * * * 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 thatwe want to invoke the methods on
> * * * * * * * * * * * * TextHelp provider = (TextHelp) cls
> * * * * * * * * * * * * * * * * * * * * .newInstance();
> * * * * * * * * * * * * // Call the method. Sincenone of them takes arguments we just
> * * * * * * * * * * * * // pass an empty array assecond parameter.
> * * * * * * * * * * * * result = (String)method..invoke(provider, new Object[0]);
>
> * * * * * * * * } catch (IllegalArgumentException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
>
> * * * * * * * * } catch (InvocationTargetException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
>
> * * * * * * * * } catch (IllegalAccessException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
>
> * * * * * * * * } catch (ClassNotFoundException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
>
> * * * * * * * * } catch (SecurityException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
>
> * * * * * * * * } catch (NoSuchMethodException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
> * * * * * * * * } catch (InstantiationException ex) {
> * * * * * * * * * * * * ex.printStackTrace();
> * * * * * * * * }
> * * * * * * * * System.out.println("Result " + ": " + result);
> * * * * * * * * return result;
> * * * * }
>
>
>
>
>
>
>
> }

Hi,

Found the problem :-)

replacements.put("{stream}","test.TextHelp:getCurr entActivity()"); --
> replacements.put("{stream}","test.TextHelp:getCurr entActivity");

Re: Substitute value in HashMap at runtime
 

On 10/14/2011 6:54 AM, mike wrote:

>> Hi,
>>
>> I put together a more complete example

> Hi,
>
> Found the problem :-)


Yes, see why we ask for these things? ;)

Re: Substitute value in HashMap at runtime
 

On Thu, 13 Oct 2011 05:18:57 -0700 (PDT), mike
<mikaelpetterson@hotmail.com> wrote, quoted or indirectly quoted
someone who said :

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

What you need to do is create a HashMap( String, Lookup).

Your Lookup interface has a lookup method that does whatever
calculations/lookups you want.

see http://mindprod.com/jgloss/delegate.html

P.S. your code as is won't compile. There is a HashMap(Map<? extends
K, ? extends V> m) constructor, but not one you are using.

The easiest way to fix the problem is to use a separate put method.
--
Roedy Green Canadian Mind Products
http://mindprod.com
It should not be considered an error when the user starts something
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to browsers, services, editors... It is inexcusable to
punish the user by requiring some elaborate sequence to atone,
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