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Derby源代码分析 -- 服务器启动

作者: zddava  来源: JavaEye  发布时间: 2010-11-08 21:26  阅读: 2803 次  推荐: 0   原文链接   [收藏]  

  一直以来都想研究下数据库的实现原理,Derby在我眼里绝对是一个完美的切入点。首先它是100%纯Java实现,对于我这种Java程序员来说简直完美的,不需要去懂C,C++...等等无疑减少了很大的难度;其次,它是开源的,当然这个就是废话,不然我去哪里弄它的源码去。废话少说,首先简单的介绍下Derby。

  Derby的启动方式有两种,一种是网络服务器的方式,这种方式就和大家平时用的Oracle,SQL Server,DB2等等没什么区别,另外一种是嵌入式方式,是一种类似于Access的方式,在这种方式下,Derby与应用程序运行于同一个JVM下,随着应用程序的关闭而关闭(我很欣赏这个方式,呵呵)。另外,Java6中包含的Java DB其实就是Derby。具体的可以google下Derby,会有更加详细的介绍,我这里就不赘述了。

好了,简单的介绍后,来转入正题,看一下Derby服务器的启动上。

  1.首先来了解下网络服务器的方式

  Derby有几种启动方式,其中一种就是用bin目录下的startNetworkServer.bat这个脚本文件。可以大致的看一下它,可以发现Derby网络服务器方式是在org.apache.derby.drda.NetworkServerControl类启动的,并且为命令行传入一个参数start。好了,下面就可以以这个类为起点来看Derby的启动部分了。根据我对Derby源代码的大致理解,Derby的网络服务器方式的启动所涉及的类大致如下图: 下面首先来看看NetworkServerControl的源代码吧,

 

public static void main(String args[]) {
NetworkServerControlImpl server
= null;
boolean printErrors = true;
try {
server
= new NetworkServerControlImpl();

int command = server.parseArgs(args);
if (needsSecurityManager(server, command)) {
verifySecurityState(server);
installSecurityManager(server);
}
printErrors
= false;
/* 执行命令 */
server.executeWork(command);
}
catch (Exception e) {
if ((e.getMessage() == null) || !e.getMessage().equals(NetworkServerCon
trolImpl.UNEXPECTED_ERR)
|| printErrors) {
if (server != null)
server.consoleExceptionPrint(e);
else
e.printStackTrace();
}
System.exit(
1);
}
System.exit(
0);
}

  这段代码没有什么复杂的,最主要的不服是调用了server的executeWork()方法,其中server是一个NetworkServerControlImpl的实例。 executeWork()方法主要是对各种不同的参数进行不同的调用,由于我们是看的启动部分,所以就只看一部分就可以了。

 

 

public void executeWork(int command) throws Exception {
if (command == COMMAND_UNKNOWN)
return;

if (commandArgs.size() != COMMAND_ARGS[command])
consolePropertyMessage(
"DRDA_InvalidNoArgs.U", COMMANDS[command]);
int min;
int max;

switch (command) {
case COMMAND_START:
shutdownDatabasesOnShutdown
= true;
/* 开启网络服务 */
blockingStart(makePrintWriter(System.out));
break;
case COMMAND_SHUTDOWN:

......

}
}

  这里没什么可说的,主要就是要看这个blockStart()方法了,这个方法比较长,我把一些异常处理的部分去掉了

 

 

public void blockingStart(PrintWriter consoleWriter) throws Exception {
/* 1. 载入Derby的Driver */
startNetworkServer();
setLogWriter(consoleWriter);
cloudscapeLogWriter
= Monitor.getStream().getPrintWriter();
if (SanityManager.DEBUG && debugOutput) {
memCheck.showmem();
mc
= new memCheck(200000);
mc.start();
}

/* 2. 打开一个ServerSocket */
try {
serverSocket
= (ServerSocket) AccessController
.doPrivileged(
new PrivilegedExceptionAction() {
public Object run() throws IOException {
return createServerSocket();
}
});
}
catch (PrivilegedActionException e) {
......
}
catch (Exception e) {
......
}

switch (getSSLMode()) {
default:
case SSL_OFF:
consolePropertyMessage(
"DRDA_Ready.I", new String[] { Integer.toString(portNumber), att_srvclsnm, versionString });
break;
case SSL_BASIC:
consolePropertyMessage(
"DRDA_SSLReady.I", new String[] { Integer.toString(portNumber), att_srvclsnm, versionString });
break;
case SSL_PEER_AUTHENTICATION:
consolePropertyMessage(
"DRDA_SSLClientAuthReady.I", new String[] { Integer.toString(portNumber), att_srvclsnm, versionString });
break;
}

/* 3. 新开一个ClientThread去接受用户请求 */
final ClientThread clientThread = (ClientThread) AccessController
.doPrivileged(
new PrivilegedExceptionAction() {
public Object run() throws Exception {
return new ClientThread(thisControl, serverSocket);
}
});
clientThread.start();

ManagementService mgmtService
= ((ManagementService) Monitor.getSystemModule(Module.JMX));

final Object versionMBean = mgmtService.registerMBean(new Version(getNetProductVersionHolder(), SystemPermission.SERVER), VersionMBean.class, "type=Version,jar=derbynet.jar");
final Object networkServerMBean = mgmtService.registerMBean(new NetworkServerMBeanImpl(this), NetworkServerMBean.class,"type=NetworkServer");

/* 直到shutdown或者出现InterruptedException,否则一直wait() */
synchronized (shutdownSync) {
try {
shutdownSync.wait();
}
catch (InterruptedException e) {
shutdown
= true;
}
}

AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
if (mc != null)
mc.interrupt();

clientThread.interrupt();
return null;
}
});

/* 关闭Session连接 */
synchronized (sessionTable) {
for (Enumeration e = sessionTable.elements(); e.hasMoreElements();) {
Session session
= (Session) e.nextElement();
session.close();
}
}

/* 关闭DRDA协议客户端连接 */
synchronized (threadList) {
for (int i = 0; i < threadList.size(); i++) {
final DRDAConnThread threadi = (DRDAConnThread) threadList.get(i);
threadi.close();
AccessController.doPrivileged(
new PrivilegedAction() {
public Object run() {
threadi.interrupt();
return null;
}
});
}
threadList.clear();
}

/* 关闭ServerSocket */
try {
serverSocket.close();
}
catch (IOException e) {
consolePropertyMessage(
"DRDA_ListenerClose.S", true);
}

/* 唤醒等待中的线程 */
synchronized (runQueue) {
runQueue.notifyAll();
}

mgmtService.unregisterMBean(versionMBean);
mgmtService.unregisterMBean(networkServerMBean);

/* 关闭Derby */
if (shutdownDatabasesOnShutdown) {
try {
if (cloudscapeDriver != null) {
final Properties p = new Properties();
if (userArg != null) {
p.setProperty(
"user", userArg);
}
if (passwordArg != null) {
p.setProperty(
"password", passwordArg);
}
cloudscapeDriver.connect(
"jdbc:derby:;shutdown=true", p);
}
}
catch (SQLException sqle) {
......
}
}

consolePropertyMessage(
"DRDA_ShutdownSuccess.I", new String[] { att_srvclsnm, versionString });
}

 

  这段代码有3个地方需要仔细研究下,分别在上述代码中用注释标注的1,2,3处。首先来看一下第1处,就是Derby驱动的载入,

 

private ServerSocket createServerSocket() throws IOException {
if (hostAddress == null)
hostAddress
= InetAddress.getByName(hostArg);
// 创建本地地址列表
buildLocalAddressList(hostAddress);

// 根据不同的情况来创建Socket
switch (getSSLMode()) {
case SSL_OFF:
default:
ServerSocketFactory sf
= ServerSocketFactory.getDefault();
return sf.createServerSocket(portNumber, 0, hostAddress);
case SSL_BASIC:
SSLServerSocketFactory ssf
= (SSLServerSocketFactory) SSLServerSocketFactory
.getDefault();
return (SSLServerSocket) ssf.createServerSocket(portNumber, 0,
hostAddress);
case SSL_PEER_AUTHENTICATION:
SSLServerSocketFactory ssf2
= (SSLServerSocketFactory) SSLServerSocketFactory
.getDefault();
SSLServerSocket sss2
= (SSLServerSocket) ssf2.createServerSocket(
portNumber,
0, hostAddress);
sss2.setNeedClientAuth(
true);
return sss2;
}
}

  最后一个部分是新开一个ClientThread去接受用户请求,由于ClientThread是一个线程类,可以看下它的#run()的实现。

 

 

public void run() {
Socket clientSocket
= null;

for (;;) { // 用一个死循环去不断的处理客户端连接

try { // 捕获所有异常的try

try { // 捕获InterruptedException,SSLException和IOException

try { // 捕获PrivilegedActionException
/* 从ServerSocket获得Socket */
clientSocket
= (Socket) AccessController
.doPrivileged(
new PrivilegedExceptionAction() {
public Object run() throws IOException {
return serverSocket.accept();
}
});
/* 判断服务器是否关闭了 */
if (parent.getShutdown()) {
clientSocket.close();
return;
}
/* 设定属性 */
clientSocket.setKeepAlive(parent.getKeepAlive());

if (timeSlice > 0)
clientSocket.setSoTimeout(timeSlice);

/* 加入Session队列 */
parent.addSession(clientSocket);

}
catch (PrivilegedActionException e) {
throw e.getException();
}

}
catch (InterruptedException ie) {
return;

}
catch (javax.net.ssl.SSLException ssle) {
parent.consoleExceptionPrintTrace(ssle);
parent.directShutdownInternal();
return;

}
catch (IOException ioe) {
synchronized (parent.getShutdownSync()) {
if (!parent.getShutdown()) {
parent.consoleExceptionPrintTrace(ioe);
if (clientSocket != null)
clientSocket.close();
}
}
return;
}
}
catch (Exception e) {
parent.consoleExceptionPrintTrace(e);
try {
if (clientSocket != null)
clientSocket.close();
}
catch (IOException closeioe) {
parent.consoleExceptionPrintTrace(closeioe);
}
}

}

}

  这样,当有新的Socket请求到了服务器时,会把这个请求加入到NetworkServerControlImpl的Session队列中等待处理。

 

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