Require Java version 1.6 or later

INSTALL.md

@@ -53,7 +53,7 @@ Mandatory dependencies:
 
 Optional:
 
- * Java compiler and SDK
+ * Java compiler and SDK 1.6.0 or later
  * ALSA sound library and headers (present on Linux, not on Android)
 
 Test dependencies:

configure.ac

@@ -79,8 +79,24 @@ AC_PROG_JAVAC
 popdef([AC_MSG_ERROR])
 AC_SUBST([JAVAC])
 
-dnl Check for JNI includes, keep going if not present.
+dnl Check Java version, ditch Java if not adequate
 if test -n "$JAVAC"; then
+    dnl Discover the version of the Java compiler
+    AC_PROG_JAVAC_VERSION
+    dnl Check that the Java compiler is modern enough
+    AS_CASE($ax_cv_prog_javac_version,
+            [[1.[6-9].*|1.[1-9][0-9].*|2.*]], [],
+            [''], [ dnl
+                AC_MSG_WARN([Java version not detected; omitting Java API])
+                JAVAC=""
+            ], [ dnl
+                AC_MSG_WARN([Java version $ax_cv_prog_javac_version is too old; omitting Java API])
+                JAVAC=""
+            ])
+fi
+
+if test -n "$JAVAC"; then
+    dnl Discover the locations of JNI header files
     dnl *** Kludge: override AC_MSG_ERROR because AC_JNI_INCLUDE_DIR does not have
     dnl *** [if-found] and [if-not-found] action parameters.
     pushdef([AC_MSG_ERROR], defn([AC_MSG_WARN]))

m4/ax_prog_javac_version.m4

@@ -0,0 +1,59 @@
+# SYNOPSIS
+#
+#   AX_PROG_JAVAC_VERSION
+#
+# DESCRIPTION
+#
+#   Discover the version of the java compiler by invoking it with the -version
+#   option and stripping off any leading "javac " word.  Cache the result in
+#   $ac_cv_prog_javac_version
+#
+# LICENSE
+#
+#   Copyright (C) 2017 Flinders University
+#
+#   This program is free software; you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation; either version 2 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, Flinders University gives unlimited permission to
+#   copy, distribute and modify the configure scripts that are the output of
+#   Autoconf when processing the Macro. You need not follow the terms of the
+#   GNU General Public License when using or distributing such scripts, even
+#   though portions of the text of the Macro appear in them. The GNU General
+#   Public License (GPL) does govern all other use of the material that
+#   constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by Flinders University. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 1
+
+AU_ALIAS([AC_PROG_JAVAC_VERSION], [AX_PROG_JAVAC_VERSION])
+AC_DEFUN([AX_PROG_JAVAC_VERSION],[
+    AC_REQUIRE([AC_PROG_SED])
+    AC_CACHE_CHECK([Java compiler version],
+                   ax_cv_prog_javac_version,
+                   [ dnl
+        dnl Many javac print their version number on standard output
+        if AC_TRY_COMMAND([$JAVAC -version >java_version 2>&1]); then
+            ax_cv_prog_javac_version=`sed -n 's/^javac //p' java_version`
+        else
+            AC_MSG_ERROR([The Java compiler $JAVAC failed (see config.log)])
+            ax_cv_prog_javac_version=""
+        fi
+        rm -f java_version
+    ])
+    AC_PROVIDE([$0])dnl
+])