How do I get the Java classpath?

By Wayan in Core API, Management 0 Comment

The RuntimeMXBean.getClassPath() returns the Java class path that is used by the system class loader to search for class files. This method is equivalent to System.getProperty("java.class.path").

Multiple paths in the Java class path are separated by the path separator character of the platform of the Java virtual machine being monitored.

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

public class GetClassPath {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();
        String classPath = bean.getClassPath();
        System.out.println("ClassPath = " + classPath);
    }
}

How do I get system properties information?

By Wayan in Core API, Management 0 Comment 
package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.util.Map;
import java.util.Set;

public class GetSystemProperties {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Returns a map of names and values of all system
        // properties. This method calls System.getProperties()
        // to get all system properties. Properties whose
        // name or value is not a String are omitted.
        Map<String, String> systemProperties = bean.getSystemProperties();
        Set<String> keys = systemProperties.keySet();
        for (String key : keys) {
            String value = systemProperties.get(key);
            System.out.printf("Property[%s] = %s%n", key, value);
        }
    }
}

Some properties produced by the code snippet above are:

Property[java.specification.version] = 17
Property[sun.cpu.isalist] = amd64
Property[sun.jnu.encoding] = Cp1252
Property[java.vm.vendor] = Oracle Corporation
Property[sun.arch.data.model] = 64
Property[user.variant] = 
Property[java.vendor.url] = https://java.oracle.com/
...
...
Property[java.vm.info] = mixed mode, sharing.
Property[java.vendor] = Oracle Corporation.
Property[java.vm.version] = 17+35-LTS-2724.
Property[sun.io.unicode.encoding] = UnicodeLittle.
Property[java.class.version] = 61.0.

How do I get the start time of a JVM?

By Wayan in Core API, Management 0 Comment 
package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.util.Date;

public class GetStartTime {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Returns the start time of the Java virtual machine in 
        // milliseconds. This method returns the approximate time 
        // when the Java virtual machine started.
        long startTime = bean.getStartTime();
        Date startDate = new Date(startTime);
        System.out.println("Start Time = " + startTime);
        System.out.println("Start Date = " + startDate);
    }
}

The result of the code snippet above:

Start Time = 1634391703196
Start Date = Sat Oct 16 21:41:43 CST 2021

How do I get the uptime of a JVM?

By Wayan in Core API, Management 0 Comment

The following code snippet demonstrates how to get the time for how long has the JVM been running.

package org.kodejava.lang.management;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;

public class GetUptime {
    public static void main(String[] args) {
        RuntimeMXBean bean = ManagementFactory.getRuntimeMXBean();

        // Returns the uptime of the Java virtual machine in
        // milliseconds.
        long uptime = bean.getUptime();
        System.out.printf("Uptime = %d (ms).", uptime);
    }
}

The output of the code snippet above:

Uptime = 125 (ms).

How do I limit MySQL query result?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class SqlLimitExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Create PreparedStatement to get all data from a database.
            String query = "select count(*) from product";
            PreparedStatement ps = connection.prepareStatement(query);
            ResultSet result = ps.executeQuery();

            int total = 0;
            while (result.next()) {
                total = result.getInt(1);
            }

            System.out.println("Total number of data in database: " +
                               total + "\n");

            // Create PreparedStatement to the first 5 records only.
            query = "select * from product limit 5";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("Result fetched with specified limit 5");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }

            // Create PreparedStatement to get data from the 4th
            // record (remember the first record is 0) and limited
            // to 3 records only.
            query = "select * from product limit 3, 3";
            ps = connection.prepareStatement(query);
            result = ps.executeQuery();

            System.out.println("\nResult fetched with specified limit 3, 3");
            System.out.println("====================================");
            while (result.next()) {
                System.out.println("id:" + result.getInt("id") +
                                   ", code:" + result.getString("code") +
                                   ", name:" + result.getString("name") +
                                   ", price:" + result.getString("price"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

An example result of our program is:

Total number of data in database: 9

Result fetched with specified limit 5
====================================
id:1, code:P0000001, name:UML Distilled 3rd Edition, price:25.00
id:3, code:P0000003, name:PHP Programming, price:20.00
id:4, code:P0000004, name:Longman Active Study Dictionary, price:40.00
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00

Result fetched with specified limit 3, 3
====================================
id:5, code:P0000005, name:Ruby on Rails, price:24.00
id:6, code:P0000006, name:Championship Manager, price:0.00
id:7, code:P0000007, name:Transport Tycoon Deluxe, price:0.00

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.4.0</version>
</dependency>

Maven Central