How could I read Java Console Output into a String buffer -

i have java program outputs text console. uses print, println, , other methods this.

at end of program , want read text in console , copy string buffer. how in java ? need read stdout , stderr separately.

ok, fun problem. dosen't seem elegant way of solving printstream methods @ once. (unfortunately there no filterprintstream.)

i did write ugly reflection-based workaround though (not used in production code suppose :)

class loggedprintstream extends printstream {      final stringbuilder buf;     final printstream underlying;      loggedprintstream(stringbuilder sb, outputstream os, printstream ul) {         super(os);         this.buf = sb;         this.underlying = ul;     }      public static loggedprintstream create(printstream tolog) {         try {             final stringbuilder sb = new stringbuilder();             field f = filteroutputstream.class.getdeclaredfield("out");             f.setaccessible(true);             outputstream psout = (outputstream) f.get(tolog);             return new loggedprintstream(sb, new filteroutputstream(psout) {                 public void write(int b) throws ioexception {                     super.write(b);                     sb.append((char) b);                 }             }, tolog);         } catch (nosuchfieldexception shouldnothappen) {         } catch (illegalargumentexception shouldnothappen) {         } catch (illegalaccessexception shouldnothappen) {         }         return null;     } } 

...that can used this:

public class test {     public static void main(string[] args) {          // create logged printstreams         loggedprintstream lpsout = loggedprintstream.create(system.out);         loggedprintstream lpserr = loggedprintstream.create(system.err);          // set them stdout / stderr         system.setout(lpsout);         system.seterr(lpserr);          // print stuff         system.out.print("hello ");         system.out.println(5);         system.out.flush();          system.err.println("some error");         system.err.flush();          // restore system.out / system.err         system.setout(lpsout.underlying);         system.seterr(lpserr.underlying);          // print logged output         system.out.println("----- log system.out: -----\n" + lpsout.buf);         system.out.println("----- log system.err: -----\n" + lpserr.buf);     } } 

resulting output:

hello 5 error ----- log system.out: ----- hello 5  ----- log system.err: ----- error 

(note though, out field in filteroutputstream protected , documented, part of api :-)