Merge pull request #11927 from kpentaris/resultset-count

Example code for Get the Number of Rows in a ResultSet

persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/RowCounterApp.java

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+package com.baeldung.resultsetrowcount;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.SQLException;
+import java.sql.Statement;
+
+class RowCounterApp {
+
+    public static void main(String[] args) throws SQLException {
+        Connection conn = createDummyDB();
+
+        String selectQuery = "SELECT * FROM STORAGE";
+
+        StandardRowCounter standardCounter = new StandardRowCounter(conn);
+        assert standardCounter.getQueryRowCount(selectQuery) == 3;
+
+        ScrollableRowCounter scrollableCounter = new ScrollableRowCounter(conn);
+        assert scrollableCounter.getQueryRowCount(selectQuery) == 3;
+    }
+
+    static Connection createDummyDB() throws SQLException {
+        String dbUrl = "jdbc:h2:mem:storagedb";
+        Connection conn = DriverManager.getConnection(dbUrl);
+        try (Statement statement = conn.createStatement()) {
+            String sql = "CREATE TABLE STORAGE (id INTEGER not null, val VARCHAR(50), PRIMARY KEY (id))";
+            statement.executeUpdate(sql);
+            sql = "INSERT INTO STORAGE VALUES (1, 'Entry A')";
+            statement.executeUpdate(sql);
+            sql = "INSERT INTO STORAGE VALUES (2, 'Entry A')";
+            statement.executeUpdate(sql);
+            sql = "INSERT INTO STORAGE VALUES (3, 'Entry A')";
+            statement.executeUpdate(sql);
+        }
+        return conn;
+    }
+
+}

persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/ScrollableRowCounter.java

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+package com.baeldung.resultsetrowcount;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+
+/**
+ * A ResultSet counter that uses a scrollable cursor.
+ * Scrollable cursors must be supported by the underlying JDBC driver
+ * and will not always be available for use.
+ */
+class ScrollableRowCounter {
+
+    Connection conn;
+
+    ScrollableRowCounter(Connection conn) {
+        this.conn = conn;
+    }
+
+    int getQueryRowCount(String query) throws SQLException {
+        try (Statement statement = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY); ResultSet scrollableRS = statement.executeQuery(query)) {
+            scrollableRS.last(); // check if we need a scrollable type for this (probably)
+            return scrollableRS.getRow();
+            // if we want to process the result set data we can move the cursor back to
+            // the beginning using the scrollableRS.beforeFirst() method
+        }
+    }
+
+}

persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/StandardRowCounter.java

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+package com.baeldung.resultsetrowcount;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+
+/**
+ * A ResultSet counter that iterates through the query
+ * results and increments a counter variable until it
+ * reaches the last result.
+ *
+ * This solution will work on all cases but is ineffective,
+ * especially if the ResultSet will be discarded afterwards.
+ */
+class StandardRowCounter {
+    Connection conn;
+
+    StandardRowCounter(Connection conn) {
+        this.conn = conn;
+    }
+
+    int getQueryRowCount(String query) throws SQLException {
+        try (Statement statement = conn.createStatement(); ResultSet standardRS = statement.executeQuery(query)) {
+            int size = 0;
+            while (standardRS.next()) {
+                size++;
+            }
+            return size;
+        }
+    }
+}

persistence-modules/core-java-persistence-2/src/test/java/com/baeldung/resultsetrowcount/ScrollableRowCounterUnitTest.java

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+package com.baeldung.resultsetrowcount;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+
+class ScrollableRowCounterUnitTest {
+
+    Connection conn;
+
+    @BeforeEach
+    void setUp() throws SQLException {
+        conn = RowCounterApp.createDummyDB();
+    }
+
+    @AfterEach
+    void tearDown() throws SQLException {
+        conn.close();
+    }
+
+    @Test
+    public void givenDummyDBWithThreeRows_whenAskingForScrollableRowCountForSelectStar_thenCountIsThree() throws SQLException {
+        ScrollableRowCounter counter = new ScrollableRowCounter(conn);
+
+        int queryRowCount = counter.getQueryRowCount("SELECT * FROM STORAGE");
+
+        Assertions.assertEquals(3, queryRowCount);
+    }
+
+    @Test
+    public void givenDummyDBWithThreeRows_whenAskingForScrollableRowCountForSelect1and2_thenCountIsTwo() throws SQLException {
+        ScrollableRowCounter counter = new ScrollableRowCounter(conn);
+
+        int queryRowCount = counter.getQueryRowCount("SELECT * FROM STORAGE WHERE ID IN (1,2)");
+
+        Assertions.assertEquals(2, queryRowCount);
+    }
+
+}

persistence-modules/core-java-persistence-2/src/test/java/com/baeldung/resultsetrowcount/StandardRowCounterUnitTest.java

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+package com.baeldung.resultsetrowcount;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+
+class StandardRowCounterUnitTest {
+
+    Connection conn;
+
+    @BeforeEach
+    void setUp() throws SQLException {
+        conn = RowCounterApp.createDummyDB();
+    }
+
+    @AfterEach
+    void tearDown() throws SQLException {
+        conn.close();
+    }
+
+    @Test
+    public void givenDummyDBWithThreeRows_whenAskingForStandardRowCountForSelectStar_thenCountIsThree() throws SQLException {
+        StandardRowCounter counter = new StandardRowCounter(conn);
+
+        int queryRowCount = counter.getQueryRowCount("SELECT * FROM STORAGE");
+
+        Assertions.assertEquals(3, queryRowCount);
+    }
+
+    @Test
+    public void givenDummyDBWithThreeRows_whenAskingForStandardRowCountForSelect1and2_thenCountIsTwo() throws SQLException {
+        StandardRowCounter counter = new StandardRowCounter(conn);
+
+        int queryRowCount = counter.getQueryRowCount("SELECT * FROM STORAGE WHERE ID IN (1,2)");
+
+        Assertions.assertEquals(2, queryRowCount);
+    }
+
+}