Chapter12

Chapter 12: Network Clients

12.1 HTTP/REST Web Client

Problem

You need to read from a URL, for example, to connect to a RESTful web service or to download a web page or other resource over HTTP/HTTPS.

Solution

Use the standard Java 11 HttpClient or the URLConnection class.

This technique applies anytime you need to read from a URL, not just a RESTful web service.

12.2 Contacting a Socket Server

Problem

You need to contact a server using TCP/IP.

Solution

Just create a java.net.Socket, passing the hostname and port number into the constructor.

12.3 Finding and Reporting Network Addresses

Problem

You want to look up a host’s address name or number or get the address at the other end of a network connection.

Solution

Get an InetAddress object.

12.5 Reading and Writing Textual Data

Problem

Having connected, you wish to transfer textual data.

Solution

Construct a BufferedReader or PrintWriter from the socket’s getInputStream() or getOutputStream().

Example:

BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

12.6 Reading and Writing Binary or Serialized Data

Problem

Having connected, you wish to transfer binary data, either raw binary data or serialized Java objects.

Solution

For plain binary data, construct a DataInputStream or DataOutputStream from the socket’s getInputStream() or getOutputStream(). For serialized Java object data, construct an ObjectInputStream or ObjectOutputStream.

If the volume of data might be large, insert a buffered stream for efficiency:

DataInputStream is = new DataInputStream(new BufferedInputStream(sock.getInputStream()));
DataOutputStream is = new DataOutputStream(new BufferedOutputStream(sock.getOutputStream()));

12.7 UDP Datagrams

Problem

You need to use a datagram connection (UDP) instead of a stream connection (TCP).

Solution

Use DatagramSocket and DatagramPacket.