reject singleton ConnectionProvider when given to NonBlockingConnecti…

…onPool builder #34

rxjava2-jdbc/src/main/java/org/davidmoten/rx/jdbc/ConnectionProvider.java

@@ -8,6 +8,7 @@
 import javax.annotation.Nonnull;
 
 import org.davidmoten.rx.jdbc.exceptions.SQLRuntimeException;
+import org.davidmoten.rx.jdbc.internal.SingletonConnectionProvider;
 
 import com.github.davidmoten.guavamini.Preconditions;
 
@@ -44,19 +45,8 @@ public interface ConnectionProvider {
      * @return singleton connection provider (don't use with connection pools!)
      */
     static ConnectionProvider from(@Nonnull Connection connection) {
-        Preconditions.checkNotNull(connection, "connection cannot be null");
-        return new ConnectionProvider() {
-
-            @Override
-            public Connection get() {
-                return connection;
-            }
-
-            @Override
-            public void close() {
-                // do nothing as con was not created by this provider
-            }
-        };
+        Preconditions.checkNotNull(connection, "connection  cannot be null");
+        return new SingletonConnectionProvider(connection);
     }
 
     static ConnectionProvider from(@Nonnull String url) {

rxjava2-jdbc/src/main/java/org/davidmoten/rx/jdbc/internal/SingletonConnectionProvider.java

@@ -0,0 +1,24 @@
+package org.davidmoten.rx.jdbc.internal;
+
+import java.sql.Connection;
+
+import org.davidmoten.rx.jdbc.ConnectionProvider;
+
+public final class SingletonConnectionProvider implements ConnectionProvider {
+
+    private final Connection connection;
+
+    public SingletonConnectionProvider(Connection connection) {
+        this.connection = connection;
+    }
+
+    @Override
+    public Connection get() {
+        return connection;
+    }
+
+    @Override
+    public void close() {
+        // do nothing as con was not created by this provider
+    }
+}

rxjava2-jdbc/src/main/java/org/davidmoten/rx/jdbc/pool/NonBlockingConnectionPool.java

@@ -13,6 +13,7 @@
 
 import org.davidmoten.rx.jdbc.ConnectionProvider;
 import org.davidmoten.rx.jdbc.Util;
+import org.davidmoten.rx.jdbc.internal.SingletonConnectionProvider;
 import org.davidmoten.rx.jdbc.pool.internal.HealthCheckPredicate;
 import org.davidmoten.rx.jdbc.pool.internal.PooledConnection;
 import org.davidmoten.rx.jdbc.pool.internal.SerializedConnectionListener;
@@ -69,6 +70,10 @@ public Builder(Function<NonBlockingConnectionPool, T> transform) {
          * @return this
          */
         public Builder<T> connectionProvider(ConnectionProvider cp) {
+            Preconditions.checkArgument(!(cp instanceof SingletonConnectionProvider), //
+                    "connection provider should not return a singleton connection because " //
+                    + "a pool needs control over the creation and closing of connections. " //
+                    + "Use ConnectionProvider.from(url,...) instead.");
             this.cp = cp;
             return this;
         }

rxjava2-jdbc/src/test/java/org/davidmoten/rx/jdbc/pool/NonBlockingConnectionPoolTest.java

@@ -0,0 +1,17 @@
+package org.davidmoten.rx.jdbc.pool;
+
+import java.sql.Connection;
+
+import org.davidmoten.rx.jdbc.ConnectionProvider;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+public class NonBlockingConnectionPoolTest {
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testRejectSingletonConnectionProvider() {
+        Connection con = Mockito.mock(Connection.class);
+        NonBlockingConnectionPool.builder().connectionProvider(ConnectionProvider.from(con));
+    }
+
+}