#87 Grouping stack traces into single log statements for sub-processes

src/main/java/com/jcabi/log/VerboseProcess.java

@@ -106,6 +106,16 @@ public final class VerboseProcess implements Closeable {
      */
     private transient boolean closed;
 
+    /**
+     * Maximum number of log lines for a stack trace
+     */
+    public static final int DEFUALT_MAX_LENGTH = 1000;
+
+    /**
+     * Maximum number of log lines for a stack trace
+     */
+    public static volatile int maxStackLength = DEFUALT_MAX_LENGTH;
+
     /**
      * Public ctor.
      * @param prc The process to work with
@@ -281,7 +291,7 @@ private String stdout(final boolean check) {
             this.process, result.code(), result.stdout().length(),
             System.currentTimeMillis() - start
         );
-        if (check && result.code() != 0) {
+        if (check && (result.code() != 0)) {
             throw new IllegalArgumentException(
                 Logger.format(
                     "Non-zero exit code %d: %[text]s",
@@ -389,6 +399,20 @@ private static void close(final Closeable res) {
      * Stream monitor.
      */
     private static final class Monitor implements Callable<Void> {
+
+        /**
+         * Prefix "at "
+         */
+        private static final String PREFIX_AT = "at ";
+        /**
+         * Prefix "Caused by"
+         */
+        private static final String PREFIX_CB = "Caused by";
+        /**
+         * Prefix "... "
+         */
+        private static final String PREFIX_DOTS = "... ";
+
         /**
          * Stream to read.
          */
@@ -420,6 +444,34 @@ private static final class Monitor implements Callable<Void> {
             this.output = out;
             this.level = lvl;
         }
+
+        /**
+         * Checks if line is part of a stack trace and should be appended.
+         * @param string String to check
+         * @return boolean result
+         */
+        private static boolean shouldAppend(final String string) {
+            final String leftStrip = stripStart(string);
+            return leftStrip.startsWith(PREFIX_AT) || leftStrip.startsWith(PREFIX_CB) || leftStrip.startsWith(PREFIX_DOTS);
+        }
+
+        /**
+         * Strips whitespace at beginning of String
+         * @param string String to strip
+         * @return string Stripped String
+         */
+        private static String stripStart(final String string) {
+            if ((string == null) || string.isEmpty()) {
+                return null;
+            }
+            final int stringLength = string.length();
+            int start = 0;
+            while ((start != stringLength) && Character.isWhitespace(string.charAt(start))) {
+                start++;
+            }
+            return string.substring(start);
+        }
+
         @Override
         public Void call() throws Exception {
             final BufferedReader reader = new BufferedReader(
@@ -433,6 +485,9 @@ public Void call() throws Exception {
                     new OutputStreamWriter(this.output, VerboseProcess.UTF_8)
                 );
                 try {
+                    StringBuilder sb = new StringBuilder();
+                    String previousLine = null;
+                    int lineCount = 0;
                     while (true) {
                         if (Thread.interrupted()) {
                             Logger.debug(
@@ -441,16 +496,33 @@ public Void call() throws Exception {
                             );
                             break;
                         }
+                        if (previousLine != null) {
+                            sb.append(previousLine).append(System.getProperty("line.separator"));
+                            previousLine = null;
+                        }
+
                         final String line = reader.readLine();
                         if (line == null) {
+                            if (sb.length() > 0) {
+                                final String logText = sb.toString();
+                                Logger.log(this.level, VerboseProcess.class, ">> %s", logText);
+                                writer.write(logText);
+                            }
                             break;
                         }
-                        Logger.log(
-                            this.level, VerboseProcess.class,
-                            ">> %s", line
-                        );
-                        writer.write(line);
-                        writer.newLine();
+
+                        if (shouldAppend(line) && (++lineCount < maxStackLength)) {
+                            sb.append(line).append(System.getProperty("line.separator"));
+                        } else {
+                            if (sb.length() > 0) {
+                                final String logText = sb.toString();
+                                Logger.log(this.level, VerboseProcess.class, ">> %s", logText);
+                                writer.write(logText);
+                                sb = new StringBuilder();
+                            }
+                            lineCount = 1;
+                            previousLine = line;
+                        }
                     }
                 } catch (final ClosedByInterruptException ex) {
                     Thread.interrupted();