Thread: How to capture or save the output given by java program.

I want to save the output of a java program in a file.

class Demo
{
public static void main(String arg[])
{
System.out.println("Yes!!!");
}
}


Above code is written in a file Demo.java.


I am using following code to run that file.


private static void printLines(String name, InputStream ins) throws Exception {
String line = null;
BufferedReader in = new BufferedReader(
new InputStreamReader(ins));
while ((line = in.readLine()) != null) {
System.out.println(name + " " + line);
}
}

private static void runProcess(String command) throws Exception {
Process pro = Runtime.getRuntime().exec(command);
pro.waitFor();
printLines(command + " stdout:", pro.getInputStream());
printLines(command + " stderr:", pro.getErrorStream());
pro.waitFor();
System.out.println(command + " exitValue() " + pro.exitValue());
}

public void run()
{
try {
runProcess("javac Demo.java");
runProcess("java Demo");
} catch (Exception e) {
e.printStackTrace();
}
}


When i am invoking run() it is showing an error:

00:32:54,073 INFO [STDOUT] java Demo stderr: java.lang.NoClassDefFoundError: Demo (wrong name: demo)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.lang.ClassLoader.defineClass1(Native Method)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.lang.ClassLoader.defineClass(Unknown Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.security.SecureClassLoader.defineClass(Unknow n Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.net.URLClassLoader.defineClass(Unknown Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.net.URLClassLoader.access$100(Unknown Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.net.URLClassLoader$1.run(Unknown Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.net.URLClassLoader$1.run(Unknown Source)
00:32:54,073 INFO [STDOUT] java Demo stderr: at java.security.AccessController.doPrivileged(Native Method)
00:32:54,074 INFO [STDOUT] java Demo stderr: at java.net.URLClassLoader.findClass(Unknown Source)
00:32:54,074 INFO [STDOUT] java Demo stderr: at java.lang.ClassLoader.loadClass(Unknown Source)
00:32:54,074 INFO [STDOUT] java Demo stderr: at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
00:32:54,074 INFO [STDOUT] java Demo stderr: at java.lang.ClassLoader.loadClass(Unknown Source)
00:32:54,074 INFO [STDOUT] java Demo stderr: at sun.launcher.LauncherHelper.checkAndLoadMain(Unkno wn Source)
00:32:54,074 INFO [STDOUT] java Demo stderr: Exception in thread "main"
00:32:54,074 INFO [STDOUT] java Demo exitValue() 1

Is there any method in any API through which i can get the output of simple java program.
Like there is a method Diagnostic.getDiagnostic() which returns a list of Compiler errors in a program.

i want to capture the output that goes to console.

i don't know exactly, i got this code from my friend even he doesn't know how it is working.
Do you have any idea?

public List<Diagnostic<? extends JavaFileObject>> checkCompile()
{

System.setProperty("java.home", "C:\\Program Files\\Java\\jdk1.7.0_05"); //jdk path

String fileName="E:\\ProjectExp\\Demo.java"; // file path
File[] javaFiles = new File[]{new File(fileName)};
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();
try
{
StandardJavaFileManager fileManager = compiler.getStandardFileManager(diagnostics, null, null);
Iterable<? extends JavaFileObject> compilationUnits = fileManager.getJavaFileObjectsFromFiles(Arrays.asL ist(javaFiles));
JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, diagnostics, null,
null, compilationUnits);
boolean success = task.call();
System.out.println(success);
if(!success)
// System.out.println(diagnostics.getDiagnostics());

return diagnostics.getDiagnostics();
fileManager.close();
}
catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
}
return diagnostics.getDiagnostics();
}

In the above code you just need to write the path of jdk and path of file that contains the java code.


File Nameemo.java
File Content:

public class Demo
{
public static void main(String arg[])
{
System.out.println("Yes!!!");
}
}