Source code for JAVA Networking (java.net)

Creating a URL
try {
// With components.
URL url = new URL("http","hostname", 80, "index.html");

// With a single string.
url = new URL(
"http://hostname:80/index.html");
} catch (MalformedURLException e) {
}

Parsing a URL
try {
URL url = new URL("http://hostname:80/index.html#_top_");
String protocol = url.getProtocol(); // http
String host = url.getHost(); // hostname
int port = url.getPort(); // 80
String file = url.getFile(); // index.html
String ref = url.getRef(); // _top_
} catch (MalformedURLException e) {
}

Reading Text from a URL
try {
URL url = new URL("http://hostname:80/index.html");
BufferedReader in = new BufferedReader(
new InputStreamReader(url.openStream()));

String str;
while ((str = in.readLine()) != null) {
process(str);
}
in.close();
} catch (MalformedURLException e) {
} catch (IOException e) {
}

Resolving a Hostname

Creating a Client Socket
try {
InetAddress addr = InetAddress.getByName("java.sun.com");
int port = 80;
Socket sock = new Socket(addr, port);
} catch (IOException e) {
}

Creating a Server Socket
try {
int port = 2000;
ServerSocket srv = new ServerSocket(port);

// Wait for connection from client.
Socket socket = srv.accept();
} catch (IOException e) {
}

Reading Text from a Socket
try {
BufferedReader rd = new BufferedReader(
new InputStreamReader(socket.getInputStream()));

String str;
while ((str = rd.readLine()) != null) {
process(str);

}
rd.close();
} catch (IOException e) {
}

Writing Text to a Socket
try {
BufferedWriter wr = new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream()));
wr.write("aString");
wr.flush();
} catch (IOException e) {
}

Sending a Datagram
public static void send(InetAddress dst,
int port, byte[] outbuf, int len) {
try {
DatagramPacket request = new DatagramPacket(
outbuf, len, dst, port);
DatagramSocket socket = new DatagramSocket();
socket.send(request);
} catch (SocketException e) {
} catch (IOException e) {
}
}
Receiving a Datagram
try {
byte[] inbuf = new byte[256]; // default size
DatagramSocket socket = new DatagramSocket();

// Wait for packet
DatagramPacket packet = new DatagramPacket(
inbuf, inbuf.length);
socket.receive(packet);

// Data is now in inbuf
int numBytesReceived = packet.getLength();
} catch (SocketException e) {
} catch (IOException e) {
}

Joining a Multicast Group
public void join(String groupName, int port) {
try {
MulticastSocket msocket = new MulticastSocket(port);
group = InetAddress.getByName(groupName);
msocket.joinGroup(group);
} catch (IOException e) {
}
}

Receiving from a Multicast Group
public void read(MulticastSocket msocket,
byte[] inbuf) {
try {
DatagramPacket packet = new DatagramPacket(
inbuf, inbuf.length);

// Wait for packet
msocket.receive(packet);

// Data is now in inbuf
int numBytesReceived = packet.getLength();
} catch (IOException e) {
}
}

Sending to a Multicast Group
byte[] outbuf = new byte[1024];
int port = 1234;
try {
DatagramSocket socket = new DatagramSocket();
InetAddress groupAddr = InetAddress.getByName(
"228.1.2.3");
DatagramPacket packet = new DatagramPacket(
outbuf, outbuf.length, groupAddr, port);
socket.send(packet);
} catch (SocketException e) {
} catch (IOException e) {
}
Defining and Exporting a Remote Object
1. Define the remote interface.
import java.rmi.*;

public interface RObject extends Remote {
void aMethod() throws RemoteException;
}

Looking Up a Remote Object and Invoking a Method
try {
// Look up remote object
RObject robj = (RObject) Naming.lookup(
"//localhost/RObjectServer");

// Invoke method on remote object
robj.aMethod();
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}

Passing Parameters to a Remote Method
Arguments to remote methods must be primitive, serializable, or Remote. This example demonstrates the declaration and use of all three parameter types.

1. Define the remote interface.
import java.rmi.*;

public interface RObject extends Remote {
// This parameter is primitive.
void primitiveArg(int num) throws RemoteException;

// This parameter implements Serializable.
void byValueArg(Integer num) throws RemoteException;

// This parameter implements Remote.
void byRefArg(ArgObject arg) throws RemoteException;
}

public interface ArgObject extends Remote {
int aMethod() throws RemoteException;
}

2. Define the remote object implementation.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

public class RObjectImpl extends UnicastRemoteObject implements RObject {
public RObjectImpl() throws RemoteException {
super();
}
public void primitiveArg(int num) throws RemoteException {
}
public void byValueArg(Integer num) throws RemoteException {
}
public void byRefArg(ArgObject arg) throws RemoteException {
}
}

3. Compile the remote object implementation.
> javac RObject.java RObjectImpl.java

4. Generate the skeletons and stubs.
> rmic RObjectImpl

5. Create an instance of RObjectImpl and bind it to the RMI Registry.
try {
RObject robj = new RObjectImpl();
Naming.rebind("//localhost/RObjectServer", robj);
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (RemoteException e) {
}

6. Look Up the Remote object and pass the parameters.
try {
// Look up the remote object
RObject robj = (RObject) Naming.lookup("//localhost/RObjectServer");

// Pass a primitive value as argument
robj.primitiveArg(1998);

// Pass a serializable object as argument
robj.byValueArg(new Integer(9));

// Pass a Remote object as argument
robj.byRefArg(new ArgObjectImpl());
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}
Returning Values from a Remote Method
Return values from remote methods must be primitive, serializable, or Remote. This example demonstrates the declaration and use of all three return types. 1. Define the remote interface.

import java.rmi.*;
public interface RObject extends Remote {
// This return value is primitive.
int primitiveRet() throws RemoteException;

// This return value implements Serializable.
Integer byValueRet() throws RemoteException;

// This return value implements Remote.
ArgObject byRefRet() throws RemoteException;
}

public interface ArgObject extends Remote {
int aMethod() throws RemoteException;
}

2. Define the remote object implementation.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

public class RObjectImpl extends UnicastRemoteObject
implements RObject {
public RObjectImpl() throws RemoteException {
super();
}
public int primitiveRet() throws RemoteException {
return 3000;
}
public Integer byValueRet() throws RemoteException {
return new Integer(2000);
}
public ArgObject byRefRet() throws RemoteException {
return new ArgObjectImpl();
}
}

3. Compile the remote object implementation.
> javac RObject.java RObjectImpl.java

4. Generate the skeletons and stubs.
> rmic RObjectImpl

5. Create an instance of RObjectImpl and bind it to the RMI Registry.
try {
RObject robj = new RObjectImpl();
Naming.rebind("//localhost/RObjectServer", robj);
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (RemoteException e) {
}
6. Look Up the Remote object, invoke the methods, and receive the return values.
try {
// Look up the remote object
RObject robj = (RObject) Naming.lookup(
"//localhost/RObjectServer");

// Receive the primitive value as return value
int r1 = robj.primitiveRet();

// Receive the serializable object as return value
Integer r2 = robj.byValueRet();

// Receive the Remote Object as return value
ArgObject aobj = robj.byRefRet();
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
}

Throwing an Exception from a Remote Method

1. Define the remote interface.
import java.rmi.*;

public interface RObject extends Remote {
void aMethod() throws RemoteException;
}

2. Define the remote object implementation.
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

public class RObjectImpl extends
UnicastRemoteObject implements RObject {
public RObjectImpl() throws RemoteException {
super();
}
public void aMethod() throws RemoteException {
// The actual exception must be wrapped in
// a RemoteException
throw new RemoteException(
"message", new FileNotFoundException("message"));
}
}

3. Compile the remote object implementation.
> javac RObject.java RObjectImpl.java

4. Generate the skeletons and stubs.
> rmic RObjectImpl
5. Create an instance of RObjectImpl and bind it to the RMI Registry.
try {
RObject robj = new RObjectImpl();
Naming.rebind("//localhost/RObjectServer", robj);
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (RemoteException e) {
}

6. Look up the Remote object, invoke the method, and catch the exception.
try {
// Look up the remote object.
RObject robj = (RObject) Naming.lookup(
"//localhost/RObjectServer");

// Invoke the method.
robj.aMethod();
} catch (MalformedURLException e) {
} catch (UnknownHostException e) {
} catch (NotBoundException e) {
} catch (RemoteException e) {
// Get the actual exception that was thrown.
Throwable realException = e.detail;
}

Strings (java.lang)


Constructing a String
If you are constructing a string with several appends, it may be more efficient to construct it using a StringBuffer and then convert it to an immutable String object.
StringBuffer buf = new StringBuffer("Initial Text");

// Modify
int index = 1;
buf.insert(index, "abc");
buf.append("def");

// Convert to string
String s = buf.toString();
Getting a Substring from a String
int start = 1;
int end = 4;
String substr = "aString".substring(start, end); // Str

Searching a String
String string = "aString";

// First occurrence.
int index = string.indexOf('S'); // 1

// Last occurrence.
index = string.lastIndexOf('i'); // 4

// Not found.
index = string.lastIndexOf('z'); // -1

Replacing Characters in a String
// Replace all occurrences of 'a' with 'o'
String newString = string.replace('a', 'o');

Replacing Substrings in a String
static String replace(String str,
String pattern, String replace) {
int s = 0;
int e = 0;
StringBuffer result = new StringBuffer();

while ((e = str.indexOf(pattern, s)) >= 0) {
result.append(str.substring(s, e));
result.append(replace);
s = e+pattern.length();
}
result.append(str.substring(s));
return result.toString();
}
Converting a String to Upper or Lower Case

// Convert to upper case
String upper = string.toUpperCase();

// Convert to lower case
String lower = string.toLowerCase();

Converting a String to a Number
int i = Integer.parseInt("123");
long l = Long.parseLong("123");
float f = Float.parseFloat("123.4");
double d = Double.parseDouble("123.4e10");

Converting Unicode to UTF-8
try {
String string = "\u5639\u563b";
byte[] utf8 = string.getBytes("UTF8");
} catch (UnsupportedEncodingException e) {
}

Converting UTF-8 to Unicode
public static String toUnicode(byte[] utf8buf) {
try {
return new String(utf8buf, "UTF8");
} catch (UnsupportedEncodingException e) {
}
return null;
}

Determining a Character's Unicode Block
char ch = '\u5639';
Character.UnicodeBlock block =
Character.UnicodeBlock.of(ch);

Breaking a String into Words
String aString = "word1 word2 word3";
StringTokenizer parser =
new StringTokenizer(aString);
while (parser.hasMoreTokens()) {
processWord(parser.nextToken());
}

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