feat: Create JAR file for Java native interface

Build with option `BUILD_JNI=1` would compile the Java code and create the JAR file.
The dcurl shared library `libdcurl.so` would be packaged into the JAR file
and can be extracted from it for Jave native interface easily.

Close #106.

.gitignore

@@ -8,7 +8,7 @@ docs/html
 *.obj
 *.elf
 
-# Precompiled Headers
+# Precompiled headers
 *.gch
 *.pch
 
@@ -23,3 +23,6 @@ docs/html
 *.so
 *.so.*
 *.dylib
+
+# Java bytecode
+*.class

Makefile

@@ -1,3 +1,5 @@
+VERSION = 0.2.0
+
 OUT ?= ./build
 SRC := src
 
@@ -89,7 +91,15 @@ TESTS := $(addprefix $(OUT)/test-, $(TESTS))
 LIBS = libdcurl.so
 LIBS := $(addprefix $(OUT)/, $(LIBS))
 
-all: config $(TESTS) $(LIBS)
+JARS := dcurljni-$(VERSION).jar
+JARS := $(addprefix $(OUT)/, $(JARS))
+
+PREQ := config $(TESTS) $(LIBS)
+ifeq ("$(BUILD_JNI)","1")
+PREQ += $(JARS)
+endif
+
+all: $(PREQ)
 .DEFAULT_GOAL := all
 
 OBJS = \

java/org/dltcollab/Dcurl.java

@@ -0,0 +1,43 @@
+package org.dltcollab;
+
+import java.io.*;
+import java.nio.file.Files;
+import java.nio.file.StandardCopyOption;
+
+public class Dcurl {
+    private static final String libraryName = "dcurl";
+    private static final String libraryPrefix = "lib";
+    private static final String librarySuffix = ".so";
+    private static final String libraryFileName = libraryPrefix + libraryName + librarySuffix;
+
+    public void loadLibraryFromJar() {
+        final File temp;
+        try {
+            temp = File.createTempFile(libraryPrefix + libraryName, librarySuffix);
+            if (temp.exists() && !temp.delete()) {
+                throw new RuntimeException("File: " + temp.getAbsolutePath() + " already exists and cannot be removed.");
+            }
+            if (!temp.createNewFile()) {
+                throw new RuntimeException("File: " + temp.getAbsolutePath() + " could not be created.");
+            }
+
+            if (!temp.exists()) {
+                throw new RuntimeException("File " + temp.getAbsolutePath() + " does not exist.");
+            } else {
+                temp.deleteOnExit();
+            }
+
+            // attempt to copy the library from the Jar file to the temp destination
+            try (final InputStream is = getClass().getClassLoader().getResourceAsStream(libraryFileName)) {
+                if (is == null) {
+                    throw new RuntimeException(libraryFileName + " was not found inside JAR.");
+                } else {
+                    Files.copy(is, temp.toPath(), StandardCopyOption.REPLACE_EXISTING);
+                }
+            }
+
+            System.load(temp.getAbsolutePath());
+        } catch (IOException e) {
+        }
+    }
+}

mk/java.mk

@@ -1,16 +1,17 @@
 UNAME_S := $(shell uname -s)
 
+JAVAC := $(shell which javac)
+ifndef JAVAC
+$(error "javac is not available. Please check JDK installation")
+endif
+
 # if JAVA_HOME is not set, guess it according to system configurations
 ifndef JAVA_HOME
 ifeq ($(UNAME_S),Darwin)
     # macOS
     JAVA_HOME := $(shell /usr/libexec/java_home)
 else
-# Default to Linux
-    JAVAC := $(shell which javac)
-    ifndef JAVAC
-    $(error "javac is not available. Please check JDK installation")
-    endif
+    # Default to Linux
     JAVA_HOME := $(shell readlink -f $(JAVAC) | sed "s:bin/javac::")
 endif
 endif # JAVA_HOME
@@ -60,3 +61,12 @@ jni/iri-pearldiver-exlib.c: $(OUT)/jni/iri-pearldiver-exlib.h
 $(OUT)/jni/%.o: jni/%.c
 	$(VECHO) "  CC\t$@\n"
 	$(Q)$(CC) -o $@ $(CFLAGS) $(CFLAGS_JNI) -c -MMD -MF $@.d $<
+
+java/org/dltcollab/%.class: java/org/dltcollab/%.java
+	$(VECHO) "  JAVAC\t$@\n"
+	$(Q)$(JAVAC) $<
+
+$(OUT)/dcurljni-$(VERSION).jar: $(OUT)/libdcurl.so java/org/dltcollab/Dcurl.class
+	$(VECHO) "  JAR\t$@\n"
+	$(Q)jar -cf $@ -C $(OUT) libdcurl.so
+	$(Q)jar -uf $@ -C java org/dltcollab/Dcurl.class