第15章 网络编程
历史上的网络编程都倾向于困难、复杂，而且极易出错。
程序员必须掌握与网络有关的大量细节，有时甚至要对硬件有深刻的认识。一般地，我们需要理解连网协议中不同的“层”（Layer）。而且对于每个连网库，一般都包含了数量众多的函数，分别涉及信息块的连接、打包和拆包；这些块的来回运输；以及握手等等。这是一项令人痛苦的工作。
但是，连网本身的概念并不是很难。我们想获得位于其他地方某台机器上的信息，并把它们移到这儿；或者相反。这与读写文件非常相似，只是文件存在于远程机器上，而且远程机器有权决定如何处理我们请求或者发送的数据。
Java最出色的一个地方就是它的“无痛苦连网”概念。有关连网的基层细节已被尽可能地提取出去，并隐藏在JVM以及Java的本机安装系统里进行控制。我们使用的编程模型是一个文件的模型；事实上，网络连接（一个“套接字”）已被封装到系统对象里，所以可象对其他数据流那样采用同样的方法调用。除此以外，在我们处理另一个连网问题——同时控制多个网络连接——的时候，Java内建的多线程机制也是十分方便的。
本章将用一系列易懂的例子解释Java的连网支持。
15.1 机器的标识
当然，为了分辨来自别处的一台机器，以及为了保证自己连接的是希望的那台机器，必须有一种机制能独一无二地标识出网络内的每台机器。早期网络只解决了如何在本地网络环境中为机器提供唯一的名字。但Java面向的是整个因特网，这要求用一种机制对来自世界各地的机器进行标识。为达到这个目的，我们采用了IP（互联网地址）的概念。IP以两种形式存在着：
(1) 大家最熟悉的DNS（域名服务）形式。我自己的域名是bruceeckel.com。所以假定我在自己的域内有一台名为Opus的计算机，它的域名就可以是Opus.bruceeckel.com。这正是大家向其他人发送电子函件时采用的名字，而且通常集成到一个万维网（WWW）地址里。
(2) 此外，亦可采用“四点”格式，亦即由点号（.）分隔的四组数字，比如202.98.32.111。
不管哪种情况，IP地址在内部都表达成一个由32个二进制位（bit）构成的数字（注释①），所以IP地址的每一组数字都不能超过255。利用由java.net提供的static
InetAddress.getByName()，我们可以让一个特定的Java对象表达上述任何一种形式的数字。结果是类型为InetAddress的一个对象，可用它构成一个“套接字”（Socket），大家在后面会见到这一点。
①：这意味着最多只能得到40亿左右的数字组合，全世界的人很快就会把它用光。但根据目前正在研究的新IP编址方案，它将采用128
bit的数字，这样得到的唯一性IP地址也许在几百年的时间里都不会用完。
作为运用InetAddress.getByName()一个简单的例子，请考虑假设自己有一家拨号连接因特网服务提供者（ISP），那么会发生什么情况。每次拨号连接的时候，都会分配得到一个临时IP地址。但在连接期间，那个IP地址拥有与因特网上其他IP地址一样的有效性。如果有人按照你的IP地址连接你的机器，他们就有可能使用在你机器上运行的Web或者FTP服务器程序。当然这有个前提，对方必须准确地知道你目前分配到的IP。由于每次拨号连接获得的IP都是随机的，怎样才能准确地掌握你的IP呢？
下面这个程序利用InetAddress.getByName()来产生你的IP地址。为了让它运行起来，事先必须知道计算机的名字。该程序只在Windows
95中进行了测试，但大家可以依次进入自己的“开始”、“设置”、“控制面板”、“网络”，然后进入“标识”卡片。其中，“计算机名称”就是应在命令行输入的内容。
//: WhoAmI.java
// Finds out your network address when you're
// connected to the Internet.
package c15;
import java.net.*;
public class WhoAmI {
public static void main(String[] args)
throws Exception {
if(args.length != 1) {
System.err.println(
"Usage: WhoAmI MachineName");
System.exit(1);
}
InetAddress a =
InetAddress.getByName(args[0]);
System.out.println(a);
}
} ///:~//: JabberServer.java
// Very simple server that just
// echoes whatever the client sends.
import java.io.*;
import java.net.*;
public class JabberServer {
// Choose a port outside of the range 1-1024:
public static final int PORT = 8080;
public static void main(String[] args)
throws IOException {
ServerSocket s = new ServerSocket(PORT);
System.out.println("Started: " + s);
try {
// Blocks until a connection occurs:
Socket socket = s.accept();
try {
System.out.println(
"Connection accepted: "+ socket);
BufferedReader in =
new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
// Output is automatically flushed
// by PrintWriter:
PrintWriter out =
new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
socket.getOutputStream())),true);
while (true) {
String str = in.readLine();
if (str.equals("END")) break;
System.out.println("Echoing: " + str);
out.println(str);
}
// Always close the two sockets...
} finally {
System.out.println("closing...");
socket.close();
}
} finally {
s.close();
}
}
} ///:~ServerSocket[addr=0.0.0.0,PORT=0,localport=8080] Socket[addr=127.0.0.1,PORT=1077,localport=8080]
//: JabberClient.java
// Very simple client that just sends
// lines to the server and reads lines
// that the server sends.
import java.net.*;
import java.io.*;
public class JabberClient {
public static void main(String[] args)
throws IOException {
// Passing null to getByName() produces the
// special "Local Loopback" IP address, for
// testing on one machine w/o a network:
InetAddress addr =
InetAddress.getByName(null);
// Alternatively, you can use
// the address or name:
// InetAddress addr =
// InetAddress.getByName("127.0.0.1");
// InetAddress addr =
// InetAddress.getByName("localhost");
System.out.println("addr = " + addr);
Socket socket =
new Socket(addr, JabberServer.PORT);
// Guard everything in a try-finally to make
// sure that the socket is closed:
try {
System.out.println("socket = " + socket);
BufferedReader in =
new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
// Output is automatically flushed
// by PrintWriter:
PrintWriter out =
new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
socket.getOutputStream())),true);
for(int i = 0; i < 10; i ++) {
out.println("howdy " + i);
String str = in.readLine();
System.out.println(str);
}
out.println("END");
} finally {
System.out.println("closing...");
socket.close();
}
}
} ///:~//: MultiJabberServer.java
// A server that uses multithreading to handle
// any number of clients.
import java.io.*;
import java.net.*;
class ServeOneJabber extends Thread {
private Socket socket;
private BufferedReader in;
private PrintWriter out;
public ServeOneJabber(Socket s)
throws IOException {
socket = s;
in =
new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
// Enable auto-flush:
out =
new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
socket.getOutputStream())), true);
// If any of the above calls throw an
// exception, the caller is responsible for
// closing the socket. Otherwise the thread
// will close it.
start(); // Calls run()
}
public void run() {
try {
while (true) {
String str = in.readLine();
if (str.equals("END")) break;
System.out.println("Echoing: " + str);
out.println(str);
}
System.out.println("closing...");
} catch (IOException e) {
} finally {
try {
socket.close();
} catch(IOException e) {}
}
}
}
public class MultiJabberServer {
static final int PORT = 8080;
public static void main(String[] args)
throws IOException {
ServerSocket s = new ServerSocket(PORT);
System.out.println("Server Started");
try {
while(true) {
// Blocks until a connection occurs:
Socket socket = s.accept();
try {
new ServeOneJabber(socket);
} catch(IOException e) {
// If it fails, close the socket,
// otherwise the thread will close it:
socket.close();
}
}
} finally {
s.close();
}
}
} ///:~//: MultiJabberClient.java
// Client that tests the MultiJabberServer
// by starting up multiple clients.
import java.net.*;
import java.io.*;
class JabberClientThread extends Thread {
private Socket socket;
private BufferedReader in;
private PrintWriter out;
private static int counter = 0;
private int id = counter++;
private static int threadcount = 0;
public static int threadCount() {
return threadcount;
}
public JabberClientThread(InetAddress addr) {
System.out.println("Making client " + id);
threadcount++;
try {
socket =
new Socket(addr, MultiJabberServer.PORT);
} catch(IOException e) {
// If the creation of the socket fails,
// nothing needs to be cleaned up.
}
try {
in =
new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
// Enable auto-flush:
out =
new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
socket.getOutputStream())), true);
start();
} catch(IOException e) {
// The socket should be closed on any
// failures other than the socket
// constructor:
try {
socket.close();
} catch(IOException e2) {}
}
// Otherwise the socket will be closed by
// the run() method of the thread.
}
public void run() {
try {
for(int i = 0; i < 25; i++) {
out.println("Client " + id + ": " + i);
String str = in.readLine();
System.out.println(str);
}
out.println("END");
} catch(IOException e) {
} finally {
// Always close it:
try {
socket.close();
} catch(IOException e) {}
threadcount--; // Ending this thread
}
}
}
public class MultiJabberClient {
static final int MAX_THREADS = 40;
public static void main(String[] args)
throws IOException, InterruptedException {
InetAddress addr =
InetAddress.getByName(null);
while(true) {
if(JabberClientThread.threadCount()
< MAX_THREADS)
new JabberClientThread(addr);
Thread.currentThread().sleep(100);
}
}
} ///:~//: Dgram.java
// A utility class to convert back and forth
// Between Strings and DataGramPackets.
import java.net.*;
public class Dgram {
public static DatagramPacket toDatagram(
String s, InetAddress destIA, int destPort) {
// Deprecated in Java 1.1, but it works:
byte[] buf = new byte[s.length() + 1];
s.getBytes(0, s.length(), buf, 0);
// The correct Java 1.1 approach, but it's
// Broken (it truncates the String):
// byte[] buf = s.getBytes();
return new DatagramPacket(buf, buf.length,
destIA, destPort);
}
public static String toString(DatagramPacket p){
// The Java 1.0 approach:
// return new String(p.getData(),
// 0, 0, p.getLength());
// The Java 1.1 approach:
return
new String(p.getData(), 0, p.getLength());
}
} ///:~//: ChatterServer.java
// A server that echoes datagrams
import java.net.*;
import java.io.*;
import java.util.*;
public class ChatterServer {
static final int INPORT = 1711;
private byte[] buf = new byte[1000];
private DatagramPacket dp =
new DatagramPacket(buf, buf.length);
// Can listen & send on the same socket:
private DatagramSocket socket;
public ChatterServer() {
try {
socket = new DatagramSocket(INPORT);
System.out.println("Server started");
while(true) {
// Block until a datagram appears:
socket.receive(dp);
String rcvd = Dgram.toString(dp) +
", from address: " + dp.getAddress() +
", port: " + dp.getPort();
System.out.println(rcvd);
String echoString =
"Echoed: " + rcvd;
// Extract the address and port from the
// received datagram to find out where to
// send it back:
DatagramPacket echo =
Dgram.toDatagram(echoString,
dp.getAddress(), dp.getPort());
socket.send(echo);
}
} catch(SocketException e) {
System.err.println("Can't open socket");
System.exit(1);
} catch(IOException e) {
System.err.println("Communication error");
e.printStackTrace();
}
}
public static void main(String[] args) {
new ChatterServer();
}
} ///:~//: ChatterServer.java
// A server that echoes datagrams
import java.net.*;
import java.io.*;
import java.util.*;
public class ChatterServer {
static final int INPORT = 1711;
private byte[] buf = new byte[1000];
private DatagramPacket dp =
new DatagramPacket(buf, buf.length);
// Can listen & send on the same socket:
private DatagramSocket socket;
public ChatterServer() {
try {
socket = new DatagramSocket(INPORT);
System.out.println("Server started");
while(true) {
// Block until a datagram appears:
socket.receive(dp);
String rcvd = Dgram.toString(dp) +
", from address: " + dp.getAddress() +
", port: " + dp.getPort();
System.out.println(rcvd);
String echoString =
"Echoed: " + rcvd;
// Extract the address and port from the
// received datagram to find out where to
// send it back:
DatagramPacket echo =
Dgram.toDatagram(echoString,
dp.getAddress(), dp.getPort());
socket.send(echo);
}
} catch(SocketException e) {
System.err.println("Can't open socket");
System.exit(1);
} catch(IOException e) {
System.err.println("Communication error");
e.printStackTrace();
}
}
public static void main(String[] args) {
new ChatterServer();
}
} ///:~//: Listmgr.c
// Used by NameCollector.java to manage
// the email list file on the server
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BSIZE 250
int alreadyInList(FILE* list, char* name) {
char lbuf[BSIZE];
// Go to the beginning of the list:
fseek(list, 0, SEEK_SET);
// Read each line in the list:
while(fgets(lbuf, BSIZE, list)) {
// Strip off the newline:
char * newline = strchr(lbuf, '\n');
if(newline != 0)
*newline = '\0';
if(strcmp(lbuf, name) == 0)
return 1;
}
return 0;
}
int main() {
char buf[BSIZE];
FILE* list = fopen("emlist.txt", "a+t");
if(list == 0) {
perror("could not open emlist.txt");
exit(1);
}
while(1) {
gets(buf); /* From stdin */
if(alreadyInList(list, buf)) {
printf("Already in list: %s", buf);
fflush(stdout);
}
else {
fseek(list, 0, SEEK_END);
fprintf(list, "%s\n", buf);
fflush(list);
printf("%s added to list", buf);
fflush(stdout);
}
}
} ///:~//: NameCollector.java
// Extracts email names from datagrams and stores
// them inside a file, using Java 1.02.
import java.net.*;
import java.io.*;
import java.util.*;
public class NameCollector {
final static int COLLECTOR_PORT = 8080;
final static int BUFFER_SIZE = 1000;
byte[] buf = new byte[BUFFER_SIZE];
DatagramPacket dp =
new DatagramPacket(buf, buf.length);
// Can listen & send on the same socket:
DatagramSocket socket;
Process listmgr;
PrintStream nameList;
DataInputStream addResult;
public NameCollector() {
try {
listmgr =
Runtime.getRuntime().exec("listmgr.exe");
nameList = new PrintStream(
new BufferedOutputStream(
listmgr.getOutputStream()));
addResult = new DataInputStream(
new BufferedInputStream(
listmgr.getInputStream()));
} catch(IOException e) {
System.err.println(
"Cannot start listmgr.exe");
System.exit(1);
}
try {
socket =
new DatagramSocket(COLLECTOR_PORT);
System.out.println(
"NameCollector Server started");
while(true) {
// Block until a datagram appears:
socket.receive(dp);
String rcvd = new String(dp.getData(),
0, 0, dp.getLength());
// Send to listmgr.exe standard input:
nameList.println(rcvd.trim());
nameList.flush();
byte[] resultBuf = new byte[BUFFER_SIZE];
int byteCount =
addResult.read(resultBuf);
if(byteCount != -1) {
String result =
new String(resultBuf, 0).trim();
// Extract the address and port from
// the received datagram to find out
// where to send the reply:
InetAddress senderAddress =
dp.getAddress();
int senderPort = dp.getPort();
byte[] echoBuf = new byte[BUFFER_SIZE];
result.getBytes(
0, byteCount, echoBuf, 0);
DatagramPacket echo =
new DatagramPacket(
echoBuf, echoBuf.length,
senderAddress, senderPort);
socket.send(echo);
}
else
System.out.println(
"Unexpected lack of result from " +
"listmgr.exe");
}
} catch(SocketException e) {
System.err.println("Can't open socket");
System.exit(1);
} catch(IOException e) {
System.err.println("Communication error");
e.printStackTrace();
}
}
public static void main(String[] args) {
new NameCollector();
}
} ///:~//: NameSender.java
// An applet that sends an email address
// as a datagram, using Java 1.02.
import java.awt.*;
import java.applet.*;
import java.net.*;
import java.io.*;
public class NameSender extends Applet
implements Runnable {
private Thread pl = null;
private Button send = new Button(
"Add email address to mailing list");
private TextField t = new TextField(
"type your email address here", 40);
private String str = new String();
private Label
l = new Label(), l2 = new Label();
private DatagramSocket s;
private InetAddress hostAddress;
private byte[] buf =
new byte[NameCollector.BUFFER_SIZE];
private DatagramPacket dp =
new DatagramPacket(buf, buf.length);
private int vcount = 0;
public void init() {
setLayout(new BorderLayout());
Panel p = new Panel();
p.setLayout(new GridLayout(2, 1));
p.add(t);
p.add(send);
add("North", p);
Panel labels = new Panel();
labels.setLayout(new GridLayout(2, 1));
labels.add(l);
labels.add(l2);
add("Center", labels);
try {
// Auto-assign port number:
s = new DatagramSocket();
hostAddress = InetAddress.getByName(
getCodeBase().getHost());
} catch(UnknownHostException e) {
l.setText("Cannot find host");
} catch(SocketException e) {
l.setText("Can't open socket");
}
l.setText("Ready to send your email address");
}
public boolean action (Event evt, Object arg) {
if(evt.target.equals(send)) {
if(pl != null) {
// pl.stop(); Deprecated in Java 1.2
Thread remove = pl;
pl = null;
remove.interrupt();
}
l2.setText("");
// Check for errors in email name:
str = t.getText().toLowerCase().trim();
if(str.indexOf(' ') != -1) {
l.setText("Spaces not allowed in name");
return true;
}
if(str.indexOf(',') != -1) {
l.setText("Commas not allowed in name");
return true;
}
if(str.indexOf('@') == -1) {
l.setText("Name must include '@'");
l2.setText("");
return true;
}
if(str.indexOf('@') == 0) {
l.setText("Name must preceed '@'");
l2.setText("");
return true;
}
String end =
str.substring(str.indexOf('@'));
if(end.indexOf('.') == -1) {
l.setText("Portion after '@' must " +
"have an extension, such as '.com'");
l2.setText("");
return true;
}
// Everything's OK, so send the name. Get a
// fresh buffer, so it's zeroed. For some
// reason you must use a fixed size rather
// than calculating the size dynamically:
byte[] sbuf =
new byte[NameCollector.BUFFER_SIZE];
str.getBytes(0, str.length(), sbuf, 0);
DatagramPacket toSend =
new DatagramPacket(
sbuf, 100, hostAddress,
NameCollector.COLLECTOR_PORT);
try {
s.send(toSend);
} catch(Exception e) {
l.setText("Couldn't send datagram");
return true;
}
l.setText("Sent: " + str);
send.setLabel("Re-send");
pl = new Thread(this);
pl.start();
l2.setText(
"Waiting for verification " + ++vcount);
}
else return super.action(evt, arg);
return true;
}
// The thread portion of the applet watches for
// the reply to come back from the server:
public void run() {
try {
s.receive(dp);
} catch(Exception e) {
l2.setText("Couldn't receive datagram");
return;
}
l2.setText(new String(dp.getData(),
0, 0, dp.getLength()));
}
} ///:~<HTML> <HEAD> <META CONTENT="text/html"> <TITLE> Add Yourself to Bruce Eckel's Java Mailing List </TITLE> </HEAD> <BODY LINK="#0000ff" VLINK="#800080" BGCOLOR="#ffffff"> <FONT SIZE=6><P> Add Yourself to Bruce Eckel's Java Mailing List </P></FONT> The applet on this page will automatically add your email address to the mailing list, so you will receive update information about changes to the online version of "Thinking in Java," notification when the book is in print, information about upcoming Java seminars, and notification about the “Hands-on Java Seminar” Multimedia CD. Type in your email address and press the button to automatically add yourself to this mailing list. <HR> <applet code=NameSender width=400 height=100> </applet> <HR> If after several tries, you do not get verification it means that the Java application on the server is having problems. In this case, you can add yourself to the list by sending email to <A HREF="mailto:Bruce@EckelObjects.com"> Bruce@EckelObjects.com</A> </BODY> </HTML>
<Form method="GET" ACTION="/cgi-bin/Listmgr2.exe"> <P>Name: <INPUT TYPE = "text" NAME = "name" VALUE = "" size = "40"></p> <P>Email Address: <INPUT TYPE = "text" NAME = "email" VALUE = "" size = "40"></p> <p><input type = "submit" name = "submit" > </p> </Form>
//: EncodeDemo.java
// Demonstration of URLEncoder.encode()
import java.net.*;
public class EncodeDemo {
public static void main(String[] args) {
String s = "";
for(int i = 0; i < args.length; i++)
s += args[i] + " ";
s = URLEncoder.encode(s.trim());
System.out.println(s);
}
} ///:~//: NameSender2.java
// An applet that sends an email address
// via a CGI GET, using Java 1.02.
import java.awt.*;
import java.applet.*;
import java.net.*;
import java.io.*;
public class NameSender2 extends Applet {
final String CGIProgram = "Listmgr2.exe";
Button send = new Button(
"Add email address to mailing list");
TextField name = new TextField(
"type your name here", 40),
email = new TextField(
"type your email address here", 40);
String str = new String();
Label l = new Label(), l2 = new Label();
int vcount = 0;
public void init() {
setLayout(new BorderLayout());
Panel p = new Panel();
p.setLayout(new GridLayout(3, 1));
p.add(name);
p.add(email);
p.add(send);
add("North", p);
Panel labels = new Panel();
labels.setLayout(new GridLayout(2, 1));
labels.add(l);
labels.add(l2);
add("Center", labels);
l.setText("Ready to send email address");
}
public boolean action (Event evt, Object arg) {
if(evt.target.equals(send)) {
l2.setText("");
// Check for errors in data:
if(name.getText().trim()
.indexOf(' ') == -1) {
l.setText(
"Please give first and last name");
l2.setText("");
return true;
}
str = email.getText().trim();
if(str.indexOf(' ') != -1) {
l.setText(
"Spaces not allowed in email name");
l2.setText("");
return true;
}
if(str.indexOf(',') != -1) {
l.setText(
"Commas not allowed in email name");
return true;
}
if(str.indexOf('@') == -1) {
l.setText("Email name must include '@'");
l2.setText("");
return true;
}
if(str.indexOf('@') == 0) {
l.setText(
"Name must preceed '@' in email name");
l2.setText("");
return true;
}
String end =
str.substring(str.indexOf('@'));
if(end.indexOf('.') == -1) {
l.setText("Portion after '@' must " +
"have an extension, such as '.com'");
l2.setText("");
return true;
}
// Build and encode the email data:
String emailData =
"name=" + URLEncoder.encode(
name.getText().trim()) +
"&email=" + URLEncoder.encode(
email.getText().trim().toLowerCase()) +
"&submit=Submit";
// Send the name using CGI's GET process:
try {
l.setText("Sending...");
URL u = new URL(
getDocumentBase(), "cgi-bin/" +
CGIProgram + "?" + emailData);
l.setText("Sent: " + email.getText());
send.setLabel("Re-send");
l2.setText(
"Waiting for reply " + ++vcount);
DataInputStream server =
new DataInputStream(u.openStream());
String line;
while((line = server.readLine()) != null)
l2.setText(line);
} catch(MalformedURLException e) {
l.setText("Bad URl");
} catch(IOException e) {
l.setText("IO Exception");
}
}
else return super.action(evt, arg);
return true;
}
} ///:~ String emailData =
"name=" + URLEncoder.encode(
name.getText().trim()) +
"&email=" + URLEncoder.encode(
email.getText().trim().toLowerCase()) +
"&submit=Submit";
// Send the name using CGI's GET process:
try {
l.setText("Sending...");
URL u = new URL(
getDocumentBase(), "cgi-bin/" +
CGIProgram + "?" + emailData);
l.setText("Sent: " + email.getText());
send.setLabel("Re-send");
l2.setText(
"Waiting for reply " + ++vcount);
DataInputStream server =
new DataInputStream(u.openStream());
String line;
while((line = server.readLine()) != null)
l2.setText(line);
// ...//: ShowHTML.java
import java.awt.*;
import java.applet.*;
import java.net.*;
import java.io.*;
public class ShowHTML extends Applet {
static final String CGIProgram = "MyCGIProgram";
Button send = new Button("Go");
Label l = new Label();
public void init() {
add(send);
add(l);
}
public boolean action (Event evt, Object arg) {
if(evt.target.equals(send)) {
try {
// This could be an HTML page instead of
// a CGI program. Notice that this CGI
// program doesn't use arguments, but
// you can add them in the usual way.
URL u = new URL(
getDocumentBase(),
"cgi-bin/" + CGIProgram);
// Display the output of the URL using
// the Web browser, as an ordinary page:
getAppletContext().showDocument(u);
} catch(Exception e) {
l.setText(e.toString());
}
}
else return super.action(evt, arg);
return true;
}
} ///:~//: CGITools.h
// Automatically extracts and decodes data
// from CGI GETs and POSTs. Tested with GNU C++
// (available for most server machines).
#include <string.h>
#include <vector> // STL vector
using namespace std;
// A class to hold a single name-value pair from
// a CGI query. CGI_vector holds Pair objects and
// returns them from its operator[].
class Pair {
char* nm;
char* val;
public:
Pair() { nm = val = 0; }
Pair(char* name, char* value) {
// Creates new memory:
nm = decodeURLString(name);
val = decodeURLString(value);
}
const char* name() const { return nm; }
const char* value() const { return val; }
// Test for "emptiness"
bool empty() const {
return (nm == 0) || (val == 0);
}
// Automatic type conversion for boolean test:
operator bool() const {
return (nm != 0) && (val != 0);
}
// The following constructors & destructor are
// necessary for bookkeeping in C++.
// Copy-constructor:
Pair(const Pair& p) {
if(p.nm == 0 || p.val == 0) {
nm = val = 0;
} else {
// Create storage & copy rhs values:
nm = new char[strlen(p.nm) + 1];
strcpy(nm, p.nm);
val = new char[strlen(p.val) + 1];
strcpy(val, p.val);
}
}
// Assignment operator:
Pair& operator=(const Pair& p) {
// Clean up old lvalues:
delete nm;
delete val;
if(p.nm == 0 || p.val == 0) {
nm = val = 0;
} else {
// Create storage & copy rhs values:
nm = new char[strlen(p.nm) + 1];
strcpy(nm, p.nm);
val = new char[strlen(p.val) + 1];
strcpy(val, p.val);
}
return *this;
}
~Pair() { // Destructor
delete nm; // 0 value OK
delete val;
}
// If you use this method outide this class,
// you're responsible for calling 'delete' on
// the pointer that's returned:
static char*
decodeURLString(const char* URLstr) {
int len = strlen(URLstr);
char* result = new char[len + 1];
memset(result, len + 1, 0);
for(int i = 0, j = 0; i <= len; i++, j++) {
if(URLstr[i] == '+')
result[j] = ' ';
else if(URLstr[i] == '%') {
result[j] =
translateHex(URLstr[i + 1]) * 16 +
translateHex(URLstr[i + 2]);
i += 2; // Move past hex code
} else // An ordinary character
result[j] = URLstr[i];
}
return result;
}
// Translate a single hex character; used by
// decodeURLString():
static char translateHex(char hex) {
if(hex >= 'A')
return (hex & 0xdf) - 'A' + 10;
else
return hex - '0';
}
};
// Parses any CGI query and turns it
// into an STL vector of Pair objects:
class CGI_vector : public vector<Pair> {
char* qry;
const char* start; // Save starting position
// Prevent assignment and copy-construction:
void operator=(CGI_vector&);
CGI_vector(CGI_vector&);
public:
// const fields must be initialized in the C++
// "Constructor initializer list":
CGI_vector(char* query) :
start(new char[strlen(query) + 1]) {
qry = (char*)start; // Cast to non-const
strcpy(qry, query);
Pair p;
while((p = nextPair()) != 0)
push_back(p);
}
// Destructor:
~CGI_vector() { delete start; }
private:
// Produces name-value pairs from the query
// string. Returns an empty Pair when there's
// no more query string left:
Pair nextPair() {
char* name = qry;
if(name == 0 || *name == '\0')
return Pair(); // End, return null Pair
char* value = strchr(name, '=');
if(value == 0)
return Pair(); // Error, return null Pair
// Null-terminate name, move value to start
// of its set of characters:
*value = '\0';
value++;
// Look for end of value, marked by '&':
qry = strchr(value, '&');
if(qry == 0) qry = ""; // Last pair found
else {
*qry = '\0'; // Terminate value string
qry++; // Move to next pair
}
return Pair(name, value);
}
}; ///:~class Pair {
string nm;
string val;
public:
Pair() { }
Pair(char* name, char* value) {
nm = decodeURLString(name);
val = decodeURLString(value);
}
const char* name() const { return nm.c_str(); }
const char* value() const {
return val.c_str();
}
// Test for "emptiness"
bool empty() const {
return (nm.length() == 0)
|| (val.length() == 0);
}
// Automatic type conversion for boolean test:
operator bool() const {
return (nm.length() != 0)
&& (val.length() != 0);
}//: Listmgr2.cpp
// CGI version of Listmgr.c in C++, which
// extracts its input via the GET submission
// from the associated applet. Also works as
// an ordinary CGI program with HTML forms.
#include <stdio.h>
#include "CGITools.h"
const char* dataFile = "list2.txt";
const char* notify = "Bruce@EckelObjects.com";
#undef DEBUG
// Similar code as before, except that it looks
// for the email name inside of '<>':
int inList(FILE* list, const char* emailName) {
const int BSIZE = 255;
char lbuf[BSIZE];
char emname[BSIZE];
// Put the email name in '<>' so there's no
// possibility of a match within another name:
sprintf(emname, "<%s>", emailName);
// Go to the beginning of the list:
fseek(list, 0, SEEK_SET);
// Read each line in the list:
while(fgets(lbuf, BSIZE, list)) {
// Strip off the newline:
char * newline = strchr(lbuf, '\n');
if(newline != 0)
*newline = '\0';
if(strstr(lbuf, emname) != 0)
return 1;
}
return 0;
}
void main() {
// You MUST print this out, otherwise the
// server will not send the response:
printf("Content-type: text/plain\n\n");
FILE* list = fopen(dataFile, "a+t");
if(list == 0) {
printf("error: could not open database. ");
printf("Notify %s", notify);
return;
}
// For a CGI "GET," the server puts the data
// in the environment variable QUERY_STRING:
CGI_vector query(getenv("QUERY_STRING"));
#if defined(DEBUG)
// Test: dump all names and values
for(int i = 0; i < query.size(); i++) {
printf("query[%d].name() = [%s], ",
i, query[i].name());
printf("query[%d].value() = [%s]\n",
i, query[i].value());
}
#endif(DEBUG)
Pair name = query[0];
Pair email = query[1];
if(name.empty() || email.empty()) {
printf("error: null name or email");
return;
}
if(inList(list, email.value())) {
printf("Already in list: %s", email.value());
return;
}
// It's not in the list, add it:
fseek(list, 0, SEEK_END);
fprintf(list, "%s <%s>;\n",
name.value(), email.value());
fflush(list);
fclose(list);
printf("%s <%s> added to list\n",
name.value(), email.value());
} ///:~//: POSTtest.cpp
// CGI_vector works as easily with POST as it
// does with GET. Written in "pure" C++.
#include <iostream.h>
#include "CGITools.h"
void main() {
cout << "Content-type: text/plain\n" << endl;
// For a CGI "POST," the server puts the length
// of the content string in the environment
// variable CONTENT_LENGTH:
char* clen = getenv("CONTENT_LENGTH");
if(clen == 0) {
cout << "Zero CONTENT_LENGTH" << endl;
return;
}
int len = atoi(clen);
char* query_str = new char[len + 1];
cin.read(query_str, len);
query_str[len] = '\0';
CGI_vector query(query_str);
// Test: dump all names and values
for(int i = 0; i < query.size(); i++)
cout << "query[" << i << "].name() = [" <<
query[i].name() << "], " <<
"query[" << i << "].value() = [" <<
query[i].value() << "]" << endl;
delete query_str; // Release storage
} ///:~<HTML> <HEAD> <META CONTENT="text/html"> <TITLE>A test of standard HTML POST</TITLE> </HEAD> Test, uses standard html POST <Form method="POST" ACTION="/cgi-bin/POSTtest"> <P>Field1: <INPUT TYPE = "text" NAME = "Field1" VALUE = "" size = "40"></p> <P>Field2: <INPUT TYPE = "text" NAME = "Field2" VALUE = "" size = "40"></p> <P>Field3: <INPUT TYPE = "text" NAME = "Field3" VALUE = "" size = "40"></p> <P>Field4: <INPUT TYPE = "text" NAME = "Field4" VALUE = "" size = "40"></p> <P>Field5: <INPUT TYPE = "text" NAME = "Field5" VALUE = "" size = "40"></p> <P>Field6: <INPUT TYPE = "text" NAME = "Field6" VALUE = "" size = "40"></p> <p><input type = "submit" name = "submit" > </p> </Form> </HTML>
//: POSTtest.java
// An applet that sends its data via a CGI POST
import java.awt.*;
import java.applet.*;
import java.net.*;
import java.io.*;
public class POSTtest extends Applet {
final static int SIZE = 10;
Button submit = new Button("Submit");
TextField[] t = new TextField[SIZE];
String query = "";
Label l = new Label();
TextArea ta = new TextArea(15, 60);
public void init() {
Panel p = new Panel();
p.setLayout(new GridLayout(t.length + 2, 2));
for(int i = 0; i < t.length; i++) {
p.add(new Label(
"Field " + i + " ", Label.RIGHT));
p.add(t[i] = new TextField(30));
}
p.add(l);
p.add(submit);
add("North", p);
add("South", ta);
}
public boolean action (Event evt, Object arg) {
if(evt.target.equals(submit)) {
query = "";
ta.setText("");
// Encode the query from the field data:
for(int i = 0; i < t.length; i++)
query += "Field" + i + "=" +
URLEncoder.encode(
t[i].getText().trim()) +
"&";
query += "submit=Submit";
// Send the name using CGI's POST process:
try {
URL u = new URL(
getDocumentBase(), "cgi-bin/POSTtest");
URLConnection urlc = u.openConnection();
urlc.setDoOutput(true);
urlc.setDoInput(true);
urlc.setAllowUserInteraction(false);
DataOutputStream server =
new DataOutputStream(
urlc.getOutputStream());
// Send the data
server.writeBytes(query);
server.close();
// Read and display the response. You
// cannot use
// getAppletContext().showDocument(u);
// to display the results as a Web page!
DataInputStream in =
new DataInputStream(
urlc.getInputStream());
String s;
while((s = in.readLine()) != null) {
ta.appendText(s + "\n");
}
in.close();
}
catch (Exception e) {
l.setText(e.toString());
}
}
else return super.action(evt, arg);
return true;
}
} ///:~//: Lookup.java
// Looks up email addresses in a
// local database using JDBC
import java.sql.*;
public class Lookup {
public static void main(String[] args) {
String dbUrl = "jdbc:odbc:people";
String user = "";
String password = "";
try {
// Load the driver (registers itself)
Class.forName(
"sun.jdbc.odbc.JdbcOdbcDriver");
Connection c = DriverManager.getConnection(
dbUrl, user, password);
Statement s = c.createStatement();
// SQL code:
ResultSet r =
s.executeQuery(
"SELECT FIRST, LAST, EMAIL " +
"FROM people.csv people " +
"WHERE " +
"(LAST='" + args[0] + "') " +
" AND (EMAIL Is Not Null) " +
"ORDER BY FIRST");
while(r.next()) {
// Capitalization doesn't matter:
System.out.println(
r.getString("Last") + ", "
+ r.getString("fIRST")
+ ": " + r.getString("EMAIL") );
}
s.close(); // Also closes ResultSet
} catch(Exception e) {
e.printStackTrace();
}
}
} ///:~SELECT people.FIRST, people.LAST, people.EMAIL FROM people.csv people WHERE (people.LAST='Eckel') AND (people.EMAIL Is Not Null) ORDER BY people.FIRST
SELECT FIRST, LAST, EMAIL FROM people.csv people WHERE (LAST='Eckel') AND (EMAIL Is Not Null) ORDER BY FIRST
"SELECT FIRST, LAST, EMAIL " + "FROM people.csv people " + "WHERE " + "(LAST='" + args[0] + "') " + " AND (EMAIL Is Not Null) " + "ORDER BY FIRST");
//: VLookup.java
// GUI version of Lookup.java
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.sql.*;
public class VLookup extends Applet {
String dbUrl = "jdbc:odbc:people";
String user = "";
String password = "";
Statement s;
TextField searchFor = new TextField(20);
Label completion =
new Label(" ");
TextArea results = new TextArea(40, 20);
public void init() {
searchFor.addTextListener(new SearchForL());
Panel p = new Panel();
p.add(new Label("Last name to search for:"));
p.add(searchFor);
p.add(completion);
setLayout(new BorderLayout());
add(p, BorderLayout.NORTH);
add(results, BorderLayout.CENTER);
try {
// Load the driver (registers itself)
Class.forName(
"sun.jdbc.odbc.JdbcOdbcDriver");
Connection c = DriverManager.getConnection(
dbUrl, user, password);
s = c.createStatement();
} catch(Exception e) {
results.setText(e.getMessage());
}
}
class SearchForL implements TextListener {
public void textValueChanged(TextEvent te) {
ResultSet r;
if(searchFor.getText().length() == 0) {
completion.setText("");
results.setText("");
return;
}
try {
// Name completion:
r = s.executeQuery(
"SELECT LAST FROM people.csv people " +
"WHERE (LAST Like '" +
searchFor.getText() +
"%') ORDER BY LAST");
if(r.next())
completion.setText(
r.getString("last"));
r = s.executeQuery(
"SELECT FIRST, LAST, EMAIL " +
"FROM people.csv people " +
"WHERE (LAST='" +
completion.getText() +
"') AND (EMAIL Is Not Null) " +
"ORDER BY FIRST");
} catch(Exception e) {
results.setText(
searchFor.getText() + "\n");
results.append(e.getMessage());
return;
}
results.setText("");
try {
while(r.next()) {
results.append(
r.getString("Last") + ", "
+ r.getString("fIRST") +
": " + r.getString("EMAIL") + "\n");
}
} catch(Exception e) {
results.setText(e.getMessage());
}
}
}
public static void main(String[] args) {
VLookup applet = new VLookup();
Frame aFrame = new Frame("Email lookup");
aFrame.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
aFrame.add(applet, BorderLayout.CENTER);
aFrame.setSize(500,200);
applet.init();
applet.start();
aFrame.setVisible(true);
}
} ///:~//: PerfectTimeI.java
// The PerfectTime remote interface
package c15.ptime;
import java.rmi.*;
interface PerfectTimeI extends Remote {
long getPerfectTime() throws RemoteException;
} ///:~//: PerfectTime.java
// The implementation of the PerfectTime
// remote object
package c15.ptime;
import java.rmi.*;
import java.rmi.server.*;
import java.rmi.registry.*;
import java.net.*;
public class PerfectTime
extends UnicastRemoteObject
implements PerfectTimeI {
// Implementation of the interface:
public long getPerfectTime()
throws RemoteException {
return System.currentTimeMillis();
}
// Must implement constructor to throw
// RemoteException:
public PerfectTime() throws RemoteException {
// super(); // Called automatically
}
// Registration for RMI serving:
public static void main(String[] args) {
System.setSecurityManager(
new RMISecurityManager());
try {
PerfectTime pt = new PerfectTime();
Naming.bind(
"//colossus:2005/PerfectTime", pt);
System.out.println("Ready to do time");
} catch(Exception e) {
e.printStackTrace();
}
}
} ///:~//: DisplayPerfectTime.java
// Uses remote object PerfectTime
package c15.ptime;
import java.rmi.*;
import java.rmi.registry.*;
public class DisplayPerfectTime {
public static void main(String[] args) {
System.setSecurityManager(
new RMISecurityManager());
try {
PerfectTimeI t =
(PerfectTimeI)Naming.lookup(
"//colossus:2005/PerfectTime");
for(int i = 0; i < 10; i++)
System.out.println("Perfect time = " +
t.getPerfectTime());
} catch(Exception e) {
e.printStackTrace();
}
}
} ///:~