ch08.html

java2高级编程

Connection Driver. </EM>
The <EM CLASS="CODE">
JDCConnectionDriver</EM>
<A NAME="marker-1087567"></A> class implements the <EM CLASS="CODE">
java.sql.Driver</EM>
 interface, which provides methods to load drivers and create new database connections. A <EM CLASS="CODE">
JDCConnectionDriver</EM>
<A NAME="marker-1087569"></A> object is created by the application seeking a database connection. The application provides the database URL for the database, login user ID, and login password. </P>
<P CLASS="Body">
<A NAME="pgfId-1087570"></A>The <EM CLASS="CODE">
JDCConnectionDriver</EM>
 constructor does the following: </P>
<UL>
<LI CLASS="BL">
<A NAME="pgfId-1087571"></A>Registers the <EM CLASS="CODE">
JDCConnectionDriver</EM>
 object with the <EM CLASS="CODE">
DriverManager</EM>
</LI>
<LI CLASS="BL">
<A NAME="pgfId-1087572"></A>Loads the <EM CLASS="CODE">
Driver</EM>
 class passed to the constructor by the calling program</LI>
<LI CLASS="BL">
<A NAME="pgfId-1087573"></A>Initializes a <EM CLASS="CODE">
JDCConnectionPool</EM>
 object for the connections with the database URL, login user ID, and login password passed to the constructor by the calling program</LI>
</UL>
<P CLASS="Body">
<A NAME="pgfId-1087574"></A>When the calling program needs a database connection, it calls the <EM CLASS="CODE">
JDCConnectionDriver.connect</EM>
 method, which in turn, calls the <EM CLASS="CODE">
JDCConnectionPool.getConnection</EM>
 method. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087577"></A><A NAME="marker-1087575"></A><A NAME="marker-1087576"></A>package pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087578"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087579"></A>import java.sql.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087580"></A>import java.util.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087581"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087582"></A>public class JDCConnectionDriver implements Driver {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087583"></A>  public static final String URL_PREFIX = &quot;jdbc:jdc:&quot;;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087584"></A>  private static final int MAJOR_VERSION = 1;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087585"></A>  private static final int MINOR_VERSION = 0;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087586"></A>  private JDCConnectionPool pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087587"></A>  public JDCConnectionDriver(String driver, String url,  
                            String user, String password) </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087588"></A>                            throws ClassNotFoundException, </PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087589"></A>                            InstantiationException, IllegalAccessException,</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087590"></A>                            SQLException {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087591"></A>   DriverManager.registerDriver(this);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087592"></A>   Class.forName(driver).newInstance();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087593"></A>   pool = new JDCConnectionPool(url, user, password);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087594"></A>}</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087595"></A>  public Connection connect(String url, Properties props) throws SQLException {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087596"></A>    if(!url.startsWith(URL_PREFIX) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087597"></A>      return null;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087598"></A>    }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087599"></A>    return pool.getConnection();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087600"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087601"></A>  public boolean acceptsURL(String url) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087602"></A>    return url.startsWith(URL_PREFIX);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087603"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087604"></A>  public int getMajorVersion() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087605"></A>    return MAJOR_VERSION;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087606"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087607"></A>  public int getMinorVersion() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087608"></A>    return MINOR_VERSION;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087609"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087610"></A>  public DriverPropertyInfo[] getPropertyInfo(String str, Properties props) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087611"></A>    return new DriverPropertyInfo[0];</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087612"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087613"></A>  public boolean jdbcCompliant() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087614"></A>    return false;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087615"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087616"></A>}</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087618"></A><EM CLASS="Bold">
Connection Pool. </EM>
The <EM CLASS="CODE">
JDCConnectionPool</EM>
<A NAME="marker-1087617"></A> class makes connections available to a calling program in its <EM CLASS="CODE">
getConnection</EM>
<A NAME="marker-1087619"></A> method. This method searches for an available connection in the connection pool. If no connection is available from the pool, a new connection is created. If a connection is available from the pool, the <EM CLASS="CODE">
getConnection</EM>
 method leases the connection and returns it to the calling program. </P>
<PRE CLASS="CODE"><A NAME="pgfId-1087622"></A><A NAME="marker-1087620"></A><A NAME="marker-1087621"></A>package pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087623"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087624"></A>import java.sql.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087625"></A>import java.util.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087626"></A>import java.io.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087627"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087628"></A>class ConnectionReaper extends Thread {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087629"></A>  private JDCConnectionPool pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087630"></A>  private final long delay=300000;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087631"></A>  ConnectionReaper(JDCConnectionPool pool) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087632"></A>    this.pool=pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087633"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087634"></A>  public void run() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087635"></A>    while(true) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087636"></A>      try {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087637"></A>        sleep(delay);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087638"></A>      } catch( InterruptedException e) { }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087639"></A>        pool.reapConnections();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087640"></A>      }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087641"></A>    }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087642"></A>}</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087643"></A>public class JDCConnectionPool {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087644"></A>  private Vector connections;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087645"></A>  private String url, user, password;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087646"></A>  final private long timeout=60000;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087647"></A>  private ConnectionReaper reaper;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087648"></A>  final private int poolsize=10;
</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087649"></A>  public JDCConnectionPool(String url, String user, String password) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087650"></A>    this.url = url;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087651"></A>    this.user = user;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087652"></A>    this.password = password;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087653"></A>    connections = new Vector(poolsize);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087654"></A>    reaper = new ConnectionReaper(this);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087655"></A>    reaper.start();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087656"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087657"></A>  public synchronized void reapConnections() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087658"></A>    long stale = System.currentTimeMillis() - timeout;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087659"></A>    Enumeration connlist = connections.elements();</PRE>
<PRE CLASS="CODE-caption"><A NAME="pgfId-1087661"></A>//API Ref: <A NAME="97708"></A>boolean hasMoreElements()</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087666"></A>     <A NAME="methods"></A><A NAME="java.util.Enumeration class"></A><A NAME="Enumeration class"></A><A NAME="hasMoreElements method"></A>while((connlist != null) &amp;&amp; (connlist.hasMoreElements())) {</PRE>
<PRE CLASS="CODE-caption"><A NAME="pgfId-1087668"></A>//API Ref: <A NAME="34919"></A>Object nextElement()</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087671"></A>      <A NAME="methods"></A><A NAME="nextElement method"></A>JDCConnection conn = (JDCConnection)connlist.nextElement();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087672"></A>        if((conn.inUse()) &amp;&amp; (stale &gt;conn.getLastUse()) &amp;&amp; (!conn.validate())) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087673"></A>         removeConnection(conn);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087674"></A>       }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087675"></A>     }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087676"></A>   }
</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087677"></A>  public synchronized void closeConnections() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087678"></A>    Enumeration connlist = connections.elements();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087679"></A>    while((connlist != null) &amp;&amp; (connlist.hasMoreElements())) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087680"></A>      JDCConnection conn = (JDCConnection)connlist.nextElement();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087681"></A>       removeConnection(conn);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087682"></A>     }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087683"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087684"></A>  private synchronized void removeConnection(JDCConnection conn) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087685"></A>    connections.removeElement(conn);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087686"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087687"></A>  public synchronized Connection getConnection() throws SQLException {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087688"></A>    JDCConnection c;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087689"></A>    for(int i = 0; i &lt; connections.size(); i++) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087690"></A>       c = (JDCConnection)connections.elementAt(i);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087691"></A>       if(c.lease()) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087692"></A>         return c;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087693"></A>       }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087694"></A>     }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087695"></A>     Connection conn = DriverManager.getConnection(url, user, password);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087696"></A>     c = new JDCConnection(conn, this);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087697"></A>     c.lease();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087698"></A>     connections.addElement(c);</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087699"></A>     return c;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087700"></A>  } 
</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087701"></A>  public synchronized void returnConnection(JDCConnection conn) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087702"></A>    conn.expireLease();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087703"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087704"></A>}</PRE>
<P CLASS="Body">
<A NAME="pgfId-1087705"></A>&nbsp;</P>
<P CLASS="Body">
<A NAME="pgfId-1087707"></A>The <A NAME="marker-1087706"></A>JDCConnection class represents a JDBC connection in the connection pool, and is essentially a wrapper around a real JDBC connection. The <EM CLASS="CODE">
JDCConnection</EM>
 object maintains a state flag to indicate if the connection is in use and the time the connection was taken from the pool. This time is used by the <EM CLASS="CODE">
ConnectionReaper</EM>
<A NAME="marker-1087708"></A> class to identify hanging connections.</P>
<PRE CLASS="CODE"><A NAME="pgfId-1087711"></A><A NAME="marker-1087709"></A><A NAME="marker-1087710"></A>package pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087712"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087713"></A>import java.sql.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087714"></A>import java.util.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087715"></A>import java.io.*;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087716"></A>&nbsp;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087717"></A>public class JDCConnection implements Connection {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087718"></A>  private JDCConnectionPool pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087719"></A>  private Connection conn;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087720"></A>  private boolean inuse;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087721"></A>  private long timestamp;
</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087722"></A>  public JDCConnection(Connection conn, JDCConnectionPool pool) {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087723"></A>    this.conn=conn;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087724"></A>    this.pool=pool;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087725"></A>    this.inuse=false;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087726"></A>    this.timestamp=0;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087727"></A>  }</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087728"></A>  public synchronized boolean lease() {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087729"></A>    if(inuse)  {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087730"></A>      return false;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087731"></A>    } else {</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087732"></A>      inuse=true;</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087733"></A>      timestamp=System.currentTimeMillis();</PRE>
<PRE CLASS="CODE"><A NAME="pgfId-1087734"></A>      return true;</PRE>