[mongodb] Support to connect MongoDB without authentication (#642)

flink-connector-mongodb-cdc/src/main/java/com/ververica/cdc/connectors/mongodb/MongoDBSource.java

@@ -19,6 +19,7 @@
 package com.ververica.cdc.connectors.mongodb;
 
 import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.annotation.VisibleForTesting;
 
 import com.mongodb.ConnectionString;
 import com.mongodb.client.model.changestream.FullDocument;
@@ -321,14 +322,18 @@ public class MongoDBSource {
         }
 
         /** Build connection uri. */
-        private ConnectionString buildConnectionUri() {
+        @VisibleForTesting
+        public ConnectionString buildConnectionUri() {
             StringBuilder sb = new StringBuilder(MONGODB_SCHEME).append("://");
 
-            if (username != null && password != null) {
-                sb.append(encodeValue(username)).append(":").append(encodeValue(password));
+            if (StringUtils.isNotEmpty(username) && StringUtils.isNotEmpty(password)) {
+                sb.append(encodeValue(username))
+                        .append(":")
+                        .append(encodeValue(password))
+                        .append("@");
             }
 
-            sb.append("@").append(checkNotNull(hosts));
+            sb.append(checkNotNull(hosts));
 
             if (StringUtils.isNotEmpty(connectionOptions)) {
                 sb.append("/?").append(connectionOptions);

flink-connector-mongodb-cdc/src/test/java/com/ververica/cdc/connectors/mongodb/MongoDBSourceTest.java

@@ -35,6 +35,7 @@ import org.apache.flink.util.Collector;
 import org.apache.flink.util.Preconditions;
 
 import com.jayway.jsonpath.JsonPath;
+import com.mongodb.ConnectionString;
 import com.mongodb.client.MongoCollection;
 import com.mongodb.client.model.Filters;
 import com.mongodb.client.model.Updates;
@@ -347,6 +348,31 @@ public class MongoDBSourceTest extends MongoDBTestBase {
         }
     }
 
+    @Test
+    public void testConnectionUri() {
+        String hosts = MONGODB_CONTAINER.getHostAndPort();
+
+        ConnectionString case0 = MongoDBSource.builder().hosts(hosts).buildConnectionUri();
+        assertEquals(String.format("mongodb://%s", hosts), case0.toString());
+
+        ConnectionString case1 =
+                MongoDBSource.builder().username("").hosts(hosts).buildConnectionUri();
+        assertEquals(String.format("mongodb://%s", hosts), case1.toString());
+
+        ConnectionString case2 =
+                MongoDBSource.builder().password("").hosts(hosts).buildConnectionUri();
+        assertEquals(String.format("mongodb://%s", hosts), case2.toString());
+
+        ConnectionString case3 =
+                MongoDBSource.builder()
+                        .username(FLINK_USER)
+                        .password(FLINK_USER_PASSWORD)
+                        .hosts(hosts)
+                        .buildConnectionUri();
+        assertEquals(FLINK_USER, case3.getUsername());
+        assertEquals(FLINK_USER_PASSWORD, new String(case3.getPassword()));
+    }
+
     // ------------------------------------------------------------------------------------------
     // Utilities
     // ------------------------------------------------------------------------------------------