BAEL-4789 Check if a database table exists (#10565)

* BAEL-4789 Check if a database table exists

* BAEL-4789 fix db credentials

* BAEL-4789 fix test method name

persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/tableexists/DatabaseConfig.java

@@ -0,0 +1,21 @@
+package com.baeldung.tableexists;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+
+class DatabaseConfig {
+    static Connection connect() throws ClassNotFoundException, SQLException {
+        Class.forName("org.h2.Driver");
+        String url = "jdbc:h2:mem:testdb";
+        return DriverManager.getConnection(url, "user", "password");
+    }
+
+    static void createTables(Connection connection) throws SQLException {
+        connection.createStatement().executeUpdate("create table EMPLOYEE (id int primary key auto_increment, name VARCHAR(255))");
+    }
+
+    static void dropTables(Connection connection) throws SQLException {
+        connection.createStatement().executeUpdate("drop table EMPLOYEE");
+    }
+}

persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/tableexists/TableChecker.java

@@ -0,0 +1,35 @@
+package com.baeldung.tableexists;
+
+import java.sql.*;
+
+class TableChecker {
+    static void printAllTables(Connection connection, String tableName) throws SQLException {
+        DatabaseMetaData databaseMetaData = connection.getMetaData();
+        ResultSet resultSet = databaseMetaData.getTables(null, null, tableName, new String[] {"TABLE"});
+
+        while (resultSet.next()) {
+            String name = resultSet.getString("TABLE_NAME");
+            String schema = resultSet.getString("TABLE_SCHEM");
+            System.out.println(name + " on schema " + schema);
+        }
+    }
+
+    static boolean tableExists(Connection connection, String tableName) throws SQLException {
+        DatabaseMetaData meta = connection.getMetaData();
+        ResultSet resultSet = meta.getTables(null, null, tableName, new String[] {"TABLE"});
+
+        return resultSet.next();
+    }
+
+    static boolean tableExistsSQL(Connection connection, String tableName) throws SQLException {
+        PreparedStatement preparedStatement = connection.prepareStatement("SELECT count(*) " +
+                "FROM information_schema.tables " +
+                "WHERE table_name = ?" +
+                "LIMIT 1;");
+        preparedStatement.setString(1, tableName);
+
+        ResultSet resultSet = preparedStatement.executeQuery();
+        resultSet.next();
+        return resultSet.getInt(1) != 0;
+    }
+}

persistence-modules/core-java-persistence-2/src/test/java/com/baeldung/tableexists/TableCheckerTest.java

@@ -0,0 +1,70 @@
+package com.baeldung.tableexists;
+
+import org.junit.jupiter.api.Test;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class TableCheckerUnitTest {
+
+    @Test
+    void givenCreatedTable_shouldFindTable() throws SQLException, ClassNotFoundException {
+        // given
+        Connection connection = DatabaseConfig.connect();
+        DatabaseConfig.createTables(connection);
+
+        // when
+        boolean tableExists = TableChecker.tableExists(connection, "EMPLOYEE");
+
+        // then
+        TableChecker.printAllTables(connection, null);
+        assertTrue(tableExists);
+
+        DatabaseConfig.dropTables(connection);
+    }
+
+    @Test
+    void givenCreatedTable_shouldFindTableWithSQL() throws SQLException, ClassNotFoundException {
+        // given
+        Connection connection = DatabaseConfig.connect();
+        DatabaseConfig.createTables(connection);
+
+        // when
+        boolean tableExists = TableChecker.tableExistsSQL(connection, "EMPLOYEE");
+
+        // then
+        TableChecker.printAllTables(connection, null);
+        assertTrue(tableExists);
+
+        DatabaseConfig.dropTables(connection);
+    }
+
+    @Test
+    void givenNoTable_shouldNotFindTable() throws SQLException, ClassNotFoundException {
+        // given
+        Connection connection = DatabaseConfig.connect();
+
+        // when
+        boolean tableExists = TableChecker.tableExists(connection, "EMPLOYEE");
+
+        // then
+        TableChecker.printAllTables(connection, null);
+        assertFalse(tableExists);
+    }
+
+    @Test
+    void givenNoTable_shouldNotFindTableWithSQL() throws SQLException, ClassNotFoundException {
+        // given
+        Connection connection = DatabaseConfig.connect();
+
+        // when
+        boolean tableExists = TableChecker.tableExistsSQL(connection, "EMPLOYEE");
+
+        // then
+        TableChecker.printAllTables(connection, null);
+        assertFalse(tableExists);
+    }
+}