From: Emmanuel Bourg <ebourg@apache.org>
Date: Mon, 16 Jan 2023 23:22:18 +0100
Subject: Adds a log formatter suitable for systemd

Forwarded: no
---
 java/org/apache/juli/SystemdFormatter.java | 109 +++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 java/org/apache/juli/SystemdFormatter.java

--- /dev/null
+++ b/java/org/apache/juli/SystemdFormatter.java
@@ -0,0 +1,109 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.juli;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.TreeMap;
+import java.util.logging.Formatter;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+
+/**
+ * Formatter suitable for logs handled by systemd/journald:
+ * <ul>
+ *   <li>Timestamps are removed (already added by journald)</li>
+ *   <li>Messages are prefixed with a marker specifying the log level. For example:
+ *     <pre>    &lt;6&gt;Tomcat started</pre>
+ *   </li>
+ *   <li>Tabulations are replaced by spaces (they are escaped as <tt>#011</tt> in /var/log/syslog otherwise)</li>
+ * </ul>
+ *
+ * If systemd isn't enabled the format falls back to the default one-line format.
+ */
+public class SystemdFormatter extends Formatter {
+
+    /** Default formatter if Tomcat isn't managed by systemd */
+    private final Formatter defaultFormatter = new OneLineFormatter();
+
+    private boolean systemdEnabled = System.getenv("INVOCATION_ID") != null && System.getenv("JOURNAL_STREAM") != null;
+
+    /** Mapping between JUL levels and systemd logging levels */
+    private TreeMap<Integer, String> levelMapping = new TreeMap<>();
+    {
+        levelMapping.put(Level.OFF.intValue(),     "<0>"); // emergency
+        levelMapping.put(Level.SEVERE.intValue(),  "<2>"); // critical
+        levelMapping.put(Level.WARNING.intValue(), "<4>"); // warning
+        levelMapping.put(Level.INFO.intValue(),    "<6>"); // info
+        levelMapping.put(Level.CONFIG.intValue(),  "<6>"); // info
+        levelMapping.put(Level.FINE.intValue(),    "<7>"); // debug
+        levelMapping.put(Level.FINER.intValue(),   "<7>"); // debug
+        levelMapping.put(Level.FINEST.intValue(),  "<7>"); // debug
+    }
+
+    @Override
+    public String format(LogRecord record) {
+        if (!systemdEnabled) {
+            return defaultFormatter.format(record);
+        }
+
+        StringBuilder sb = new StringBuilder();
+
+        // Severity
+        String prefix = getSystemdLevel(record.getLevel());
+        sb.append(prefix);
+
+        // Message
+        sb.append(formatMessage(record));
+
+        // Stack trace
+        if (record.getThrown() != null) {
+            sb.append("\n").append(prefix);
+            sb.append(toString(record.getThrown())
+                            .replaceAll("\t", "    ")       // tabulations are escaped as #011 in /var/log/syslog
+                            .replaceAll("\\n", "\n" + prefix)
+            );
+        }
+
+        // New line for next record
+        sb.append(System.lineSeparator());
+
+        return sb.toString();
+    }
+
+    private String toString(Throwable t) {
+        StringWriter sw = new StringWriter();
+        PrintWriter pw = new PrintWriter(sw);
+        t.printStackTrace(pw);
+        pw.close();
+
+        return sw.toString();
+    }
+
+    /**
+     * Returns the systemd log level mapped to the specified JUL level.
+     */
+    private String getSystemdLevel(Level level) {
+        String systemdLevel = levelMapping.get(level.intValue());
+        if (systemdLevel == null) {
+            // no exact match (custom level?), pick the nearest one above
+            systemdLevel = levelMapping.ceilingEntry(level.intValue()).getValue();
+            levelMapping.put(level.intValue(), systemdLevel);
+        }
+        return systemdLevel;
+    }
+}