How to redirect output from Groovy script?

Question

I wonder if there is any way I could change the default output (System.out) for the groovy script that I'm executing from my Java code.

Here is the Java code:

public void exec(File file, OutputStream output) throws Exception {
    GroovyShell shell = new GroovyShell();
    shell.evaluate(file);
}

And the sample groovy script:

def name='World'
println "Hello $name!"

Currently the execution of the method, evaluates scripts that writes "Hello World!" to the console (System.out). How can I redirect output to the OutputStream passed as a parameter?

jjchiw · Accepted Answer · 2013-12-12 10:03:06Z

18

Try this using Binding

public void exec(File file, OutputStream output) throws Exception {
    Binding binding = new Binding()
    binding.setProperty("out", output) 
    GroovyShell shell = new GroovyShell(binding);
    shell.evaluate(file);
}

After comments

public void exec(File file, OutputStream output) throws Exception {
    Binding binding = new Binding()
    binding.setProperty("out", new PrintStream(output)) 
    GroovyShell shell = new GroovyShell(binding);
    shell.evaluate(file);
}

Groovy Script

def name='World'
out << "Hello $name!"

edited Dec 12, 2013 at 10:03

answered Oct 7, 2009 at 13:43

jjchiw

4,4301 gold badge33 silver badges32 bronze badges

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8 Comments

Tomasz Blachowicz Over a year ago

That would work, but I'd like to redirect any output written to the standard output. Especially by built-in functions such us println().

Tomasz Blachowicz Over a year ago

You were about right. The solution is to wrap the output int the java.io.PrintStream and pass as "out" property to the shell!

jjchiw Over a year ago

yay!, my first bronze badge! Happy it work it out! How did you wrap the output?

Tomasz Blachowicz Over a year ago

Congrats! Simply use new PrintStream(output) and pass as "out" property to binding.

djangofan Over a year ago

Really? binding.setProperty takes an OutputStream and somehow works without calling .write??

|

Safrain · Accepted Answer · 2013-06-27 04:03:29Z

3

How about using javax.script.ScriptEngine? You can specify its writer.

ScriptEngine engine = new ScriptEngineManager().getEngineByName("Groovy");
PrintWriter writer = new PrintWriter(new StringWriter());
engine.getContext().setWriter(writer);
engine.getContext().setErrorWriter(writer);
engine.eval("println 'HELLO'")

answered Jun 27, 2013 at 4:03

Safrain

2941 silver badge5 bronze badges

Comments

Krzysztof Atłasik · Accepted Answer · 2017-02-23 13:03:39Z

3

Use SystemOutputInterceptor class. You can start intercepting output before script evaluation and stop after.

def output = "";
def interceptor = new SystemOutputInterceptor({ output += it; false});
interceptor.start()
println("Hello")
interceptor.stop()

edited Feb 23, 2017 at 13:03

answered Dec 4, 2012 at 21:35

Krzysztof Atłasik

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Comments

Armand · Accepted Answer · 2011-11-25 13:24:47Z

2

I suspect you could do this quite nicely by overwriting the println method in your GroovyShell's metaClass. The following works in Groovy Console:

StringBuilder b = new StringBuilder()

this.metaClass.println = {
    b.append(it)
    System.out.println it
}

println "Hello, world!"
System.out.println b.toString()

output:

Hello, world!
Hello, world!

answered Nov 25, 2011 at 13:24

Armand

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Comments

fospathi · Accepted Answer · 2020-06-05 17:06:02Z

0

System.setOut() is just what you need.

edited Jun 5, 2020 at 17:06

fospathi

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answered Oct 7, 2009 at 13:52

David Winslow

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1 Comment

Tomasz Blachowicz Over a year ago

I'm afraid System.setOut is too heavyweight :) It changes the output globally for the entire JVM and this is not something that I wanted to do :)

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