[wpiutil, wpilib] Add FileLogger and log console output (#6977)

wpiutil/src/main/java/edu/wpi/first/util/FileLogger.java

@@ -0,0 +1,32 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.util;
+
+import edu.wpi.first.util.datalog.DataLog;
+
+/**
+ * A class version of `tail -f`, otherwise known as `tail -f` at home. Watches a file and puts the
+ * data into a data log. Only works on Linux-based platforms.
+ */
+public class FileLogger implements AutoCloseable {
+  private final long m_impl;
+
+  /**
+   * Construct a FileLogger. When the specified file is modified, appended data will be appended to
+   * the specified data log.
+   *
+   * @param file The path to the file.
+   * @param log A data log.
+   * @param key The log key to append data to.
+   */
+  public FileLogger(String file, DataLog log, String key) {
+    m_impl = WPIUtilJNI.createFileLogger(file, log.getImpl(), key);
+  }
+
+  @Override
+  public void close() {
+    WPIUtilJNI.freeFileLogger(m_impl);
+  }
+}

wpiutil/src/main/java/edu/wpi/first/util/WPIUtilJNI.java

@@ -217,6 +217,24 @@ public class WPIUtilJNI {
   public static native int[] waitForObjectsTimeout(int[] handles, double timeout)
       throws InterruptedException;
 
+  /**
+   * Create a native FileLogger. When the specified file is modified, appended data will be appended
+   * to the specified data log.
+   *
+   * @param file path to the file
+   * @param log data log implementation handle
+   * @param key log key to append data to
+   * @return The FileLogger handle.
+   */
+  public static native long createFileLogger(String file, long log, String key);
+
+  /**
+   * Free a native FileLogger. This causes the FileLogger to stop appending data to the log.
+   *
+   * @param fileTail The FileLogger handle.
+   */
+  public static native void freeFileLogger(long fileTail);
+
   /** Utility class. */
   protected WPIUtilJNI() {}
 }