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Example code for Get the Number of Rows in a ResultSet

This commit is contained in:
PentaKon 2022-03-14 20:16:03 +02:00
parent 2695ba0fde
commit 3c9ba66969
5 changed files with 191 additions and 0 deletions
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43
persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/RowCounterApp.java Normal file
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package com.baeldung.resultsetrowcount;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
class RowCounterApp {
static Logger logger = LoggerFactory.getLogger(RowCounterApp.class);
public static void main(String[] args) throws SQLException {
Connection conn = createDummyDB();
String selectQuery = "SELECT * FROM STORAGE";
StandardRowCounter standardCounter = new StandardRowCounter(conn);
logger.info("Standard counter count: {}", standardCounter.getQueryRowCount(selectQuery));
ScrollableRowCounter scrollableCounter = new ScrollableRowCounter(conn);
logger.info("Scrollable counter count: {}", scrollableCounter.getQueryRowCount(selectQuery));
}
static Connection createDummyDB() throws SQLException {
String dbUrl = "jdbc:h2:mem:testdb";
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;
}
}

30
persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/ScrollableRowCounter.java Normal file
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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
}
}
}

32
persistence-modules/core-java-persistence-2/src/main/java/com/baeldung/resultsetrowcount/StandardRowCounter.java Normal file
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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;
}
}
}

43
persistence-modules/core-java-persistence-2/src/test/java/com/baeldung/resultsetrowcount/ScrollableRowCounterUnitTest.java Normal file
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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);
}
}

43
persistence-modules/core-java-persistence-2/src/test/java/com/baeldung/resultsetrowcount/StandardRowCounterUnitTest.java Normal file
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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);
}
}