Merge pull request #2999 from liquibase/DAT-10419-issue-6

do not allow individual commands to close the top-level OutputStream (System.out)

liquibase-core/src/main/java/liquibase/command/CommandScope.java

@@ -4,6 +4,7 @@
 import liquibase.configuration.*;
 import liquibase.exception.CommandExecutionException;
 import liquibase.exception.CommandValidationException;
+import liquibase.io.UnclosableOutputStream;
 import liquibase.util.StringUtil;
 
 import java.io.OutputStream;
@@ -127,7 +128,12 @@ public <T> T getArgumentValue(CommandArgumentDefinition<T> argument) {
      * Think "what would be piped out", not "what the user is told about what is happening".
      */
     public CommandScope setOutput(OutputStream outputStream) {
-        this.outputStream = outputStream;
+        /*
+        This is an UncloseableOutputStream because we do not want individual command steps to inadvertently (or
+        intentionally) close the System.out OutputStream. Closing System.out renders it unusable for other command
+        steps which expect it to still be open.
+         */
+        this.outputStream = new UnclosableOutputStream(outputStream);
 
         return this;
     }

liquibase-core/src/main/java/liquibase/io/UnclosableOutputStream.java

@@ -0,0 +1,23 @@
+package liquibase.io;
+
+import java.io.FilterOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+
+/**
+ * This class is a wrapper around OutputStreams, and makes them impossible for callers to close.
+ */
+public class UnclosableOutputStream extends FilterOutputStream {
+    public UnclosableOutputStream(OutputStream out) {
+        super(out);
+    }
+
+    /**
+     * This method does not actually close the underlying stream, but rather only flushes it. Callers should not be
+     * closing the stream they are given.
+     */
+    @Override
+    public void close() throws IOException {
+        out.flush();
+    }
+}