[Java] Add static method RocksDB.loadLibrary()

Summary:
Add static method RocksDB.loadLibrary() which loads necessary library
files.

Test Plan:
make rocksdbjava
make jtest
make jdb_bench
java/jdb_bench.sh

Reviewers: haobo, dhruba, sdong, ankgup87, rsumbaly, swapnilghike, zzbennett

Reviewed By: ankgup87

CC: leveldb

Differential Revision: https://reviews.facebook.net/D18375

java/Makefile

@@ -8,7 +8,7 @@ clean:
 	rm -f $(ROCKSDB_JAR)
 
 java:
-	javac org/rocksdb/*.java org/rocksdb/util/*.java
+	javac org/rocksdb/util/*.java org/rocksdb/*.java
 	jar -cf $(ROCKSDB_JAR) org/rocksdb/*.class org/rocksdb/util/*.class
 	javah -d $(NATIVE_INCLUDE) -jni $(NATIVE_JAVA_CLASSES)
 

java/RocksDBSample.java

@@ -13,7 +13,7 @@ import java.io.IOException;
 
 public class RocksDBSample {
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
 
   public static void main(String[] args) {

java/org/rocksdb/RocksDB.java

@@ -10,6 +10,7 @@ import java.util.Map;
 import java.util.HashMap;
 import java.io.Closeable;
 import java.io.IOException;
+import org.rocksdb.util.Environment;
 
 /**
  * A RocksDB is a persistent ordered map from keys to values.  It is safe for
@@ -19,6 +20,60 @@ import java.io.IOException;
  */
 public class RocksDB {
   public static final int NOT_FOUND = -1;
+  private static final String[] compressionLibs_ = {
+      "snappy", "zlib", "bzip2", "lz4", "lz4hc"};
+
+  /**
+   * Loads the necessary library files.
+   * Calling this method twice will have no effect.
+   */
+  public static synchronized void loadLibrary() {
+    // loading possibly necessary libraries.
+    for (String lib : compressionLibs_) {
+      try {
+      System.loadLibrary(lib);
+      } catch (UnsatisfiedLinkError e) {
+        // since it may be optional, we ignore its loading failure here.
+      }
+    }
+    // However, if any of them is required.  We will see error here.
+    System.loadLibrary("rocksdbjni");
+  }
+
+  /**
+   * Tries to load the necessary library files from the given list of
+   * directories.
+   *
+   * @param paths a list of strings where each describes a directory
+   *     of a library.
+   */
+  public static synchronized void loadLibrary(List<String> paths) {
+    for (String lib : compressionLibs_) {
+      for (String path : paths) {
+        try {
+          System.load(path + "/" + Environment.getSharedLibraryName(lib));
+          break;
+        } catch (UnsatisfiedLinkError e) {
+          // since they are optional, we ignore loading fails.
+        }
+      }
+    }
+    boolean success = false;
+    UnsatisfiedLinkError err = null;
+    for (String path : paths) {
+      try {
+        System.load(path + "/" + Environment.getJniLibraryName("rocksdbjni"));
+        success = true;
+        break;
+      } catch (UnsatisfiedLinkError e) {
+        err = e;
+      }
+    }
+    if (success == false) {
+      throw err;
+    }
+  }
+
   /**
    * The factory constructor of RocksDB that opens a RocksDB instance given
    * the path to the database using the default options w/ createIfMissing

java/org/rocksdb/WriteBatchTest.java

@@ -16,7 +16,7 @@ import java.io.UnsupportedEncodingException;
  */
 public class WriteBatchTest {
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
 
   public static void main(String args[]) {

java/org/rocksdb/benchmark/DbBenchmark.java

@@ -172,7 +172,7 @@ public class DbBenchmark {
   }
 
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
 
   abstract class BenchmarkTask implements Callable<Stats> {

java/org/rocksdb/test/BackupableDBTest.java

@@ -11,7 +11,7 @@ public class BackupableDBTest {
   static final String db_path = "/tmp/backupablejni_db";
   static final String backup_path = "/tmp/backupablejni_db_backup";
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
   public static void main(String[] args) {
 

java/org/rocksdb/test/OptionsTest.java

@@ -6,11 +6,12 @@
 package org.rocksdb.test;
 
 import java.util.Random;
+import org.rocksdb.RocksDB;
 import org.rocksdb.Options;
 
 public class OptionsTest {
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
   public static void main(String[] args) {
     Options opt = new Options();

java/org/rocksdb/test/ReadOptionsTest.java

@@ -6,11 +6,12 @@
 package org.rocksdb.test;
 
 import java.util.Random;
-import org.rocksdb.*;
+import org.rocksdb.RocksDB;
+import org.rocksdb.ReadOptions;
 
 public class ReadOptionsTest {
   static {
-    System.loadLibrary("rocksdbjni");
+    RocksDB.loadLibrary();
   }
   public static void main(String[] args) {
     ReadOptions opt = new ReadOptions();

java/org/rocksdb/util/Environment.java

@@ -0,0 +1,37 @@
+package org.rocksdb.util;
+
+public class Environment {
+  private static String OS = System.getProperty("os.name").toLowerCase();
+
+  public static boolean isWindows() {
+    return (OS.indexOf("win") >= 0);
+  }
+
+  public static boolean isMac() {
+    return (OS.indexOf("mac") >= 0);
+  }
+
+  public static boolean isUnix() {
+    return (OS.indexOf("nix") >= 0 ||
+            OS.indexOf("nux") >= 0 ||
+            OS.indexOf("aix") >= 0);
+  }
+
+  public static String getSharedLibraryName(String name) {
+    if (isUnix()) {
+      return String.format("lib%s.so", name);
+    } else if (isMac()) {
+      return String.format("lib%s.dylib", name);
+    }
+    throw new UnsupportedOperationException();
+  }
+
+  public static String getJniLibraryName(String name) {
+    if (isUnix()) {
+      return String.format("lib%s.so", name);
+    } else if (isMac()) {
+      return String.format("lib%s.jnilib", name);
+    }
+    throw new UnsupportedOperationException();
+  }
+}