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-1-
provide you the possibility to configure your programs with Dynamic parameters.
for example, a configure-file looks like :

some.a=1some.property=${Math.max(256,Runtime.getRuntime().availableProcessors()*8)}some.b=2

the properties can be distributed by a configure-server or a disk file, and can be used as :

tomcat.setMaxThreads(EL.eval(config.get("some.property")));

will make your tomcat service run with correct threads number based on the machine it is running in.
this makes you use proper CPU/Memory resources for you application when it is running in different server, not a static value for all different servers in a cluster.

-2-
a command line programEL.main() can be used to parse user input, and test the logicalbefore you write them into your code.

for example:

java -cp az-el.jar az.el.EL -e a=1 System.out.println(a)

will evaluate those 2 expressions.and:

java -cp az-el.jar az.el.EL -f /home/user/file.txt

will evaluate expressions in the file, line by line.and:

java -cp az-el.jar az.el.EL -i

will evaluate expressions you entered on console. this can be used as a java-shell.

data types supported:

to supply a string in expression, please use a pair of single quotation marks,
for example:

EL.eval(newString[]{"System.out.print('some string here\n');"})

other variables which defined by user can be referenced by its name,
for example:

EL.eval("a=1;System.out.println(a*2)")

will print out "2" on console.

strings should be enclosed with a pair of '', for example:

EL.eval("a='xyz';print(a)")

will print out a string "xyz" on console.
and do not name your variables with a start character"$".

1:map()
helps creating a Map object, for example:

EL.eval("result=map('a',1,'b','2')")

will create aMap<Object,Object> named "result" with two entries of {"a"->1,"b"->"2"}.

2:list()
to create a List object, for example:

EL.eval("list(1,'a',2,3)")

will create aList<Object> collection object with 4 items in it.

3:array()
create an array, for example : array(1,2,'3').

4:each(), every(), foreach()
can be used to iterate over a collection, like list/array.for example:

EL.eval("each(a_list,'System.out.println($)')")

will print out each element on console. the collection can be an objectof typeIterator/Iterable/List/Set/Map.if you just want to print out each element of a collection,use"each(a_list_object)", the same as"each(a_list_object,'println($)')".

5:iif()
used to check given condition and then return corresponding value.for example:

x=iif(a>1, obj.doSomething(a), obj.doAnother(a))

will evaluate the sub-expression "obj.doSomething(a)" only if "a>1", and neverevaluate "obj.doAnother(a)" anyway. we delayed the expression-evaluation.

6:print(), println(), printf()
used to print something out on console,similar method-signature asSystem.out.print*() series.

+ - * / % & | ! ^ ~ >> << =!= == > < >= <= ++ --a+=1 a-=1 a*=1 a/=1 a%=2 a&=1 a|=1 a^=1

you can't feed expressions toEL.eval(String exp) method,if the string contains (;\n), useEL.eval(String[] exp) instead.

for example :

// for : Math.max(int a, int b).Math.max#int(a,b)Math.max(long_var_1,long_var_2)// for : Some.add(int a, int b).var.add#int#int(1,2)

you can specify a method what is matching the parameters-list you given,to overcome the method-overloading problem.

for example:

// for : print out a integer value.System.out.println#int(...)// for : print out a float value.System.out.println#float(...)

it's possible to provide a list of classes which shouldn't be used in code.

context.put(EL.VAR_NAME_CLASS_BLACKLIST, "a.SomeClass,b.*")

to disable some classes.

and you can setup a white-list

context.put(EL.VAR_NAME_CLASS_WHITELIST, "a.SomeClass,b.*")

to narrow down what class can be used in expression.

"java.lang.System.out.print#string('hello');System.out.println('world')""java.lang.Math.max#int(1,2)""com.some.Class.prop='word'""com.some.Class.method#string#int('a',1,?)""var=com.SomeClass.new#string('jacky');var.sayHello('iAmLucy')""2*Math.max#int(5*Runtime.getRuntime().availableProcessors(),8*3)+3*4-1""iif(a>b,c,com.SomeClass.doSomething('x'));""var=array('a','b','c');each(var,'System.out.println#string($)');""foreach(map('a',1,'b',2))"

do not use very long expressions, it's much better to be shorter than 128 chars.

contact me through :arrenzhang@hotmail.com .