Java Reference
In-Depth Information
generally quite a bit faster (the Java interpreter is already up and running, so why wait for an-
other copy of it to start up?). See
Chapter 22
.
When building industrial-strength applications, note the cautionary remarks in the Java API
docs for the
Process
class concerning the danger of losing some of the I/O due to insuffi-
cient buffering by the operating system.
Calling Other Languages via javax.script
Problem
You want to invoke a script written in some other language from within your Java program,
running in the JVM, with the ability to pass variables directly to/from the other language.
Solution
If the script you want is written in any of the two-dozen-plus supported languages, just use
javax.script
. Languages include awk, perl, python, Ruby, BeanShell, PNuts, Ksh/Bash, R
(“Renjin”), several implementations of JavaScript, and more.
Discussion
Example 24-6
is a very simple demo where we know the name of the scripting engine we
want to use.
R
is a well-known statistical computing/scripting language, itself cloned from
Bell Labs' “S” language.
Renjin
is a pure-Java reimplementation of R.
Example 24-6. RenjinScripting.java
/**
* Demonstrate interacting with the "R" implementation called "Renjin"
*/
public
public static
static
void
void
main
(
String
[]
args
)
throws
throws
ScriptException
{
ScriptEngineManager manager
=
new
new
ScriptEngineManager
();
ScriptEngine engine
=
manager
.
getEngineByName
(
"Renjin"
);
engine
.
put
(
"a"
,
42
);
Object ret
=
engine
.
eval
(
"b <- 2; a*b"
);
System
.
out
.
println
(
ret
);
}
