[KYUUBI #1645] Implement Flink engine GetSchemas operation

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### _Why are the changes needed?_
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Implement GetSchemas operation.

### _How was this patch tested?_
- [x] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.readthedocs.io/en/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #1768 from SteNicholas/KYUUBI-1645.

Closes #1645

7ff66db [SteNicholas] [KYUUBI #1645] Implement GetSchemas operation

Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: Kent Yao <yao@apache.org>

Author: SteNicholas

externals/kyuubi-flink-sql-engine/src/main/scala/org/apache/kyuubi/engine/flink/operation/FlinkSQLOperationManager.scala

@@ -47,7 +47,10 @@ class FlinkSQLOperationManager extends OperationManager("FlinkSQLOperationManage
   override def newGetSchemasOperation(
       session: Session,
       catalog: String,
-      schema: String): Operation = null
+      schema: String): Operation = {
+    val op = new GetSchemas(session, catalog, schema)
+    addOperation(op)
+  }
 
   override def newGetTablesOperation(
       session: Session,

externals/kyuubi-flink-sql-engine/src/main/scala/org/apache/kyuubi/engine/flink/operation/GetSchemas.scala

@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.kyuubi.engine.flink.operation
+
+import scala.collection.JavaConverters._
+
+import org.apache.commons.lang3.StringUtils
+import org.apache.flink.table.api.{DataTypes, ResultKind, TableEnvironment}
+import org.apache.flink.table.catalog.Column
+import org.apache.flink.types.Row
+
+import org.apache.kyuubi.engine.flink.result.ResultSet
+import org.apache.kyuubi.engine.flink.util.StringUtils.filterPattern
+import org.apache.kyuubi.operation.OperationType
+import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant._
+import org.apache.kyuubi.session.Session
+
+class GetSchemas(session: Session, catalogName: String, schema: String)
+  extends FlinkOperation(OperationType.GET_SCHEMAS, session) {
+
+  override protected def runInternal(): Unit = {
+    try {
+      val schemaPattern = toJavaRegex(schema)
+      val tableEnv: TableEnvironment = sessionContext.getExecutionContext.getTableEnvironment
+      val schemas = tableEnv.listCatalogs()
+        .filter { c => StringUtils.isEmpty(catalogName) || c == catalogName }
+        .flatMap { c =>
+          val catalog = tableEnv.getCatalog(c).get()
+          filterPattern(catalog.listDatabases().asScala, schemaPattern)
+            .map { d => Row.of(d, c) }
+        }
+      resultSet = ResultSet.builder.resultKind(ResultKind.SUCCESS_WITH_CONTENT)
+        .columns(
+          Column.physical(TABLE_SCHEM, DataTypes.STRING()),
+          Column.physical(TABLE_CATALOG, DataTypes.STRING()))
+        .data(schemas)
+        .build
+    } catch {
+      onError()
+    }
+  }
+}

externals/kyuubi-flink-sql-engine/src/test/scala/org/apache/kyuubi/engine/flink/operation/FlinkOperationSuite.scala

@@ -17,6 +17,8 @@
 
 package org.apache.kyuubi.engine.flink.operation
 
+import org.apache.flink.table.api.EnvironmentSettings.DEFAULT_BUILTIN_CATALOG
+import org.apache.flink.table.api.EnvironmentSettings.DEFAULT_BUILTIN_DATABASE
 import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatest.time.SpanSugar._
 
@@ -27,6 +29,8 @@ import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.FUNCTION_CAT
 import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.FUNCTION_NAME
 import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.FUNCTION_SCHEM
 import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.TABLE_CAT
+import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.TABLE_CATALOG
+import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.TABLE_SCHEM
 import org.apache.kyuubi.operation.meta.ResultSetSchemaConstant.TABLE_TYPE
 import org.apache.kyuubi.service.ServiceState._
 
@@ -58,6 +62,24 @@ class FlinkOperationSuite extends WithFlinkSQLEngine with HiveJDBCTestHelper {
     }
   }
 
+  test("get schemas") {
+    withJdbcStatement() { statement =>
+      val metaData = statement.getConnection.getMetaData
+      var resultSet = metaData.getSchemas(null, null)
+      while (resultSet.next()) {
+        assert(resultSet.getString(TABLE_SCHEM) == DEFAULT_BUILTIN_DATABASE)
+        assert(resultSet.getString(TABLE_CATALOG) === DEFAULT_BUILTIN_CATALOG)
+      }
+      resultSet = metaData.getSchemas(
+        DEFAULT_BUILTIN_CATALOG.split("_").apply(0),
+        DEFAULT_BUILTIN_DATABASE.split("_").apply(0))
+      while (resultSet.next()) {
+        assert(resultSet.getString(TABLE_SCHEM) == DEFAULT_BUILTIN_DATABASE)
+        assert(resultSet.getString(TABLE_CATALOG) === DEFAULT_BUILTIN_CATALOG)
+      }
+    }
+  }
+
   test("get table types") {
     withJdbcStatement() { statement =>
       val meta = statement.getConnection.getMetaData