import java.io.BufferedInputStream;
public synchronized int read() throws IOException
List<String> TRAIN = List.of("...","...");record Employee(int id){ }
var empList = List.of(new Employee(1),
new Employee(2),
new Employee(3));
System.out.println(empList);List<Integer> list = List.of(1, 2, null); // Fails with a NullPointerExceptionList<Integer> list = List.of(1, 2, 3);
list.contains(null); // Throws NullPointerExceptionList<Integer> list = List.of(1, 2, 3);
list.set(1, 10); // FailsIt takes an array or a series of elements and returns a List backed by the original array. This means any changes made to the list will directly affect the original array, and vice versa.
You can change the value of existing elements in a list but since it has a fixed size. You cannot add or remove elements from the list. Any attempt to add/remove will result in an UnsupportedOperationException.
Integer[] array = {1,2,3};
List<Integer> list = List.of(array);
array[1] = 10;
System.out.println(list); // Prints [1, 2, 3]List<Employee> empList = List.of(new Employee(1),
new Employee(2),
new Employee(3));
empList.set(0, new Employee(50));// Not Supported
System.out.println(empList);
List<Employee> empList1 = Arrays.asList(new Employee(1),
new Employee(2),
new Employee(3));
empList1.set(0, new Employee(50));// Supported
System.out.println(empList1);// Create a DatagramChannel.
DatagramChannel channel = DatagramChannel.open();
// Bind the channel to a local port.
channel.bind(new InetSocketAddress(9999));
// Join the multicast group.
InetAddress address = InetAddress.getByName("127.0.0.1");
NetworkInterface networkInterface = NetworkInterface.getByInetAddress(address);
InetAddress group = InetAddress.getByName("224.0.0.255");
channel.join(group,networkInterface);
// Create a datagram packet.
byte[] data = "Hello, world!".getBytes();
DatagramPacket packet = new DatagramPacket(data, data.length, group, 9999);
// Send the datagram packet.
channel.send(packet);
// Close the channel.
channel.close();InetAddress address = InetAddress.getByName("127.0.0.1");
NetworkInterface networkInterface = NetworkInterface.getByInetAddress(address);
InetAddress group = InetAddress.getByName("239.255.0.1")
DatagramChannel channel = DatagramChannel.open(StandardProtocolFamily.INET)
.setOption(StandardSocketOptions.SO_REUSEADDR, true)
.bind(new InetSocketAddress(5000))
.setOption(StandardSocketOptions.IP_MULTICAST_IF, networkInterface);
MembershipKey key = channel.join(group, networkInterface);// Create a DatagramSocketDatagramSocket socket = new DatagramSocket(9999);// Receive a datagram packetDatagramPacket packet = new DatagramPacket(new byte[1024], 1024);socket.receive(packet);// Get the data from the packetString data = new String(packet.getData(), 0, packet.getLength());// Send a replyString reply = "Hello, world!";DatagramPacket replyPacket = new DatagramPacket(reply.getBytes(),reply.length(),packet.getAddress(),packet.getPort());socket.send(replyPacket);
int port = 12345; // Change this to the desired port numberDatagramChannel channel = DatagramChannel.open(); channel.bind(new InetSocketAddress(port)); System.out.println("Server listening on port " + port); ByteBuffer buffer = ByteBuffer.allocate(1024); while (true) { buffer.clear(); InetSocketAddress clientAddress = (InetSocketAddress) channel.receive(buffer); buffer.flip(); // prepare for reading after data has been written into it System.out.println("Received message from " + clientAddress.getAddress() + ":" + clientAddress.getPort()); // Process the received data (here we're just echoing it back) channel.send(buffer, clientAddress);
email.host=imap.example.comemail.port=993email.protocol=imapsemail.username=your-email@example.comemail.password=your-email-password
import javax.mail.*;
import java.util.properties;
@Configuration
public class EmailConfiguration {
@Value("${email.host}")
private String emailHost;
@Value("${email.port}")
private String emailPort;
@Value("${email.username}")
private String emailUsername;
@Value("${email.password}")
private String emailPassword;
@Bean
public Session mailSession() {
Properties props = new Properties();
props.setProperty("mail.store.protocol", "imaps");
props.setProperty("mail.imaps.host", emailHost);
props.setProperty("mail.imaps.port", emailPort);
// Create a new session with the properties
Session session = Session.getInstance(props);
session.setDebug(true); // Enable debug mode for troubleshooting
return session;
}
}@Configuration
public class EmailConfiguration {
@Bean
public EmailListener emailListener() {
return new EmailListener(mailSession(), emailUsername, emailPassword);
}
}import javax.mail.*;
import javax.mail.event.MessageCountAdapter;
import javax.mail.event.MessageCountEvent;
import com.sun.mail.imap.IMAPFolder;
public class EmailListener extends MessageCountAdapter {
private Session session;
private String username;
private String password;
public EmailListener(Session session, String username, String password) {
this.session = session;
this.username = username;
this.password = password;
}
...
}import com.sun.mail.imap.IMAPFolder;
public class EmailListener extends MessageCountAdapter {
...
public void startListening() throws MessagingException, InterruptedException,
IOException {
Store store = session.getStore("imaps");
store.connect(username, password);
IMAPFolder inbox = (IMAPFolder)store.getFolder("INBOX");
inbox.open(Folder.READ_WRITE);
// Create a new thread to keep the connection alive
Thread keepAliveThread = new Thread(new KeepAliveRunnable(inbox),
"IdleConnectionKeepAlive");
keepAliveThread.start();
inbox.addMessageCountListener(new MessageCountAdapter() {
@Override
public void messagesAdded(MessageCountEvent event) {
// Process the newly added messages
Message[] messages = event.getMessages();
for (Message message : messages) {
try {
// Implement your email processing logic here
System.out.println("New email received: " + message.getSubject());
} catch (MessagingException e) {
...
}
}
}
});
// Start the IDLE Loop
while (!Thread.interrupted()) {
try {
System.out.println("Starting IDLE");
inbox.idle();
} catch (MessagingException e) {
...
throw new RuntimeException(e);
}
}
// Interrupt and shutdown the keep-alive thread
if (keepAliveThread.isAlive()) {
keepAliveThread.interrupt();
}
}
}import com.sun.mail.imap.IMAPFolder;
import javax.mail.MessagingException;
public class KeepAliveRunnable implements Runnable {
private static final long KEEP_ALIVE_FREQ = 300000; // 5 minutes
private IMAPFolder folder;
public KeepAliveRunnable(IMAPFolder folder) {
this.folder = folder;
}
@Override
public void run() {
while (!Thread.interrupted()) {
try {
Thread.sleep(KEEP_ALIVE_FREQ);
// Perform a NOOP to keep the connection alive
System.out.println("Performing a NOOP to keep the connection alive");
folder.doCommand(protocol -> {
protocol.simpleCommand("NOOP", null);
return null;
});
} catch (InterruptedException e) {
// Ignore, just aborting the thread...
} catch (MessagingException e) {
// Shouldn't really happen...
System.out.println("Unexpected exception");
e.printStackTrace();
}
}
}
}We need an email server that supports the IMAP IDLE feature. IMAP IDLE allows our application to receive immediate notifications when new messages arrive in the inbox rather than relying on periodic polling.Some servers have specific setting or timeouts that may terminate the IDLE connection after a certain period of inactivity. e.g. Gmail ~ 10 mins. So KeepAlive mechanism is necessary to receive email indefinitely.
public ResultSet getTables(String catalog, String schemaPattern, String tableNamePattern, String[] types) throws SQLException
Typical types are "TABLE", "VIEW", "SYSTEM TABLE", "GLOBAL TEMPORARY", "LOCAL TEMPORARY", "ALIAS", "SYNONYM".
TABLE_CAT : Catalog of the table.TABLE_SCHEM : Catalog of the schema.TABLE_NAME : Name of the table.TABLE_TYPE : Type of the table. (table, view, system table, global table, alias, synonym etc..)REMARKS : Comments on the column.TYPE_SCHEM : Schema of the table.TYPE_NAME : Name of the type.SELF_REFERENCING_COL_NAME : Name of the designated column of the table.REF_GENERATION : Either SYSTEM or, USER or, DERIVED.
try(ResultSet rs = conn.getMetaData().getTables(conn.getCatalog(), conn.getSchema(), null, new String[] {"TABLE"})) { ... }
try(ResultSet rs = conn.getMetaData().getTables(null,null,null,new String[] {"TABLE"})) { while (rs.next()) { System.out.println(rs.getString("TABLE_SCHEM") + "." + rs.getString("TABLE_NAME")); } } // Output app96.t1 app96.t2 public.administration$account public.appmodule$uploadedfile public.audittrail$audittrailsuperclass
record Point(int x, int y) { }
Object obj = new Point(2, 3);if (obj instanceof Point(int x, int y)) {System.out.println("x: " + x + ", y: " + y);} else {System.out.println("Not a point");}
Object shape = new Circle(5); String description = switch (shape) { case Point(int x, int y) -> "Point at (" + x + ", " + y + ")"; case Circle(int radius) -> "Circle with radius " + radius; default -> "Unknown shape"; }; System.out.println(description);