FilterIdGenerator fixes (#1544)

Don't create a new SecureRandom instance every time a filter ID is generated.
Fix intermittency in FilterIdGeneratorTest - quantity values omit leading 0s.
Signed-off-by: Adrian Sutton <adrian.sutton@consensys.net>

ethereum/jsonrpc/src/main/java/tech/pegasys/pantheon/ethereum/jsonrpc/internal/filter/FilterIdGenerator.java

@@ -15,11 +15,15 @@ package tech.pegasys.pantheon.ethereum.jsonrpc.internal.filter;
 import tech.pegasys.pantheon.crypto.SecureRandomProvider;
 import tech.pegasys.pantheon.ethereum.jsonrpc.internal.results.Quantity;
 
+import java.security.SecureRandom;
+
 public class FilterIdGenerator {
 
+  private final SecureRandom secureRandom = SecureRandomProvider.createSecureRandom();
+
   public String nextId() {
     final byte[] randomBytes = new byte[16];
-    SecureRandomProvider.createSecureRandom().nextBytes(randomBytes);
+    secureRandom.nextBytes(randomBytes);
     return Quantity.create(randomBytes);
   }
 }

ethereum/jsonrpc/src/test/java/tech/pegasys/pantheon/ethereum/jsonrpc/internal/filter/FilterIdGeneratorTest.java

@@ -14,7 +14,7 @@ package tech.pegasys.pantheon.ethereum.jsonrpc.internal.filter;
 
 import static org.junit.Assert.assertEquals;
 
-import tech.pegasys.pantheon.util.bytes.BytesValue;
+import tech.pegasys.pantheon.util.uint.UInt256;
 
 import org.junit.Test;
 
@@ -24,7 +24,7 @@ public class FilterIdGeneratorTest {
   public void idIsAHexString() {
     final FilterIdGenerator generator = new FilterIdGenerator();
     final String s = generator.nextId();
-    final BytesValue bytesValue = BytesValue.fromHexString(s);
-    assertEquals(s, bytesValue.toString());
+    final UInt256 bytesValue = UInt256.fromHexString(s);
+    assertEquals(s, bytesValue.toShortHexString());
   }
 }