dba.html

java 基础的 一点东西,,可以看看

<PRE>
&#60;HTML&#62;
&#60;BODY&#62;

&#60;APPLET CODE=DbaOdbAppl.class 
  WIDTH=200 
  HEIGHT=100&#62;
&#60;/APPLET&#62;

&#60;/BODY&#62;
&#60;/HTML&#62;
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

And here is how to start the applet:

</FONT>

<PRE>
  appletviewer DbaOdb.html
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<P>
<STRONG>Reading a Stack Trace:</STRONG>
If the <A HREF="./Code/DbaOdbAppl.java">DbaOdbAppl.java</A> applet
is launched without a policy file, the following stack trace
is generated when the end user clicks the <CODE>Click Me</CODE>
button.

</FONT>

<PRE>
  java.security.AccessControlException: access denied
  (java.lang.RuntimePermission 
  accessClassInPackage.sun.jdbc.odbc )
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

The first line in the above stack trace tells you access is denied.
This means this stack trace was generated because the applet tried to
access a system resource without the proper permission. The second
line means you need a <CODE>RuntimePermission</CODE> that gives
the applet access to the <CODE>sun.jdbc.odbc</CODE> package.
This package provides the JDBC-ODBC bridge functionality to the
Java<A HREF="#TJVM"><SUP>1</SUP></A> virtual machine (VM).

<P>
You can use Policy tool to create the policy file you need,
or you can create it with an ASCII editor. Here is the policy
file with the permission indicated by the stack trace:

</FONT>

<PRE>
grant {
  permission java.lang.RuntimePermission
    &quot;accessClassInPackage.sun.jdbc.odbc&quot;;
};
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<P>
Run the applet again, this time with a policy file named
<CODE>DbaOdbPol</CODE> that has the above permission in it:

</FONT>

<PRE>
  appletviewer -J-Djava.security.policy=DbaOdbPol 
                                         DbaOdb.html
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

You get a stack trace again, but this time it is a different
error condition.

</FONT>

<PRE>
  java.security.AccessControlException:
  access denied (java.lang.RuntimePermission
  file.encoding read)
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

The stack trace means the applet needs read permission to the encoded 
(binary) file.
Here is the <CODE>DbaOdbPol</CODE> policy file with the permission
indicated by the stack trace added to it:

</FONT>

<PRE>
  grant {
    permission java.lang.RuntimePermission
       &quot;accessClassInPackage.sun.jdbc.odbc&quot;;
    permission java.util.PropertyPermission
       &quot;file.encoding&quot;, &quot;read&quot;;
  };
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

Run the applet again. If you use the above policy file
with the Runtime and Property permissions indicated, it
works just fine.

</FONT>

<PRE>
  appletviewer -J-Djava.security.policy=DbaOdbPol 
                                         DbaOdb.html
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<A NAME="serv"></A>
<H3>Database Access by Servlets</H3>

As you learned in Lesson 6, servlets are under the security
policy in force for the web server under which they run. When
the database read and write code is added to the 
<CODE>FileIOServlet</CODE> from Lesson 6, the 
<A HREF="./Code/DbaServlet.java">DbaServlet.java</A> servlet
for this lesson executes without restriction under Java WebServer<FONT SIZE="-2"><SUP>TM</SUP></FONT> 1.1.1. 

<P>
The web server has to be configured to locate the
database. Consult your web server documentation or
database administrator for help. With Java WebServer 1.1.1,
the configuration setup involves editing the startup scripts
with such things as environment settings for loading the ODBC driver,
and locating and connecting to the database. 

<P>
<IMG SRC="./Art/dba1.gif" WIDTH="252" HEIGHT="129" ALT="">
<TABLE BORDER="0" CELLSPACING="2" CELLPADDING="2">
<TR><TD>
<IMG SRC="./Art/dba2.gif" WIDTH="247" HEIGHT="157" ALT="">
</TD></TR>
</TABLE>

</FONT>

<PRE>
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

import java.sql.*;
import java.net.*;
import java.io.*;

public class DbaServlet extends HttpServlet {

 private Connection c;
 final static private String _driver = 
	&quot;sun.jdbc.odbc.JdbcOdbcDriver&quot;;
 final static private String _user = &quot;username&quot;;
 final static private String _pass = &quot;password&quot;;
 final static private String 
			_url = &quot;jdbc:odbc:jdc&quot;;

public void doPost(HttpServletRequest request,
	HttpServletResponse response)
	throws ServletException, IOException{
  response.setContentType(&quot;text/html&quot;);
  PrintWriter out = response.getWriter();
  out.println(&quot;&#60;title&gt;Example&#60;title&gt;&quot; +
      &quot;&#60;body bgcolor=FFFFFF&gt;&quot;);

  out.println(&quot;&#60;h2&#62;Button Clicked&#60;/h2&#62;&quot;);

  String DATA = request.getParameter(&quot;DATA&quot;);

  if(DATA != null){
     out.println(&quot;&#60;STRONG&#62;Text from 
			form:&#60;/STRONG&#62;&quot;);
     out.println(DATA);
  } else {
    out.println(&quot;No text entered.&quot;);
  }

//Establish database connection
  try{
    Class.forName (_driver);
    c = DriverManager.getConnection(_url, 
				    _user,
				    _pass);
   } catch (Exception e) {
     e.printStackTrace();
     System.exit(1);
   }

   try{
//Code to write to database
     Statement stmt = c.createStatement();
     String updateString = &quot;INSERT INTO dba &quot; + 
		&quot;VALUES ('&quot; + DATA + &quot;')&quot;;
     int count = stmt.executeUpdate(updateString);

//Code to read from database
     ResultSet results = stmt.executeQuery(
		&quot;SELECT TEXT FROM dba &quot;);
     while(results.next()){
       String s = results.getString(&quot;TEXT&quot;);
       out.println(&quot;&lt;BR&gt;
         &#60;STRONG&#62;Text from database:&#60;/STRONG&#62;&quot;);
       out.println(s);
     }
      stmt.close();
     }catch(java.sql.SQLException e){
      System.out.println(e.toString());
     }

      out.println(&quot;&lt;P&gt;Return to 
        &#60;A HREF=&quot;../dbaHTML.html&quot;&#62;Form&#60;/A&#62;&quot;);
      out.close();
  }
}
</PRE>

<FONT FACE="Verdana, Arial, Helvetica, sans-serif">

<A NAME="more"></A>
<H3>More Information</H3>

You can find more information on variable access settings in the
<A HREF="http://java.sun.com/docs/books/tutorial/java/javaOO/index.html">Objects
and Classes</A> trail in
<A HREF="http://java.sun.com/docs/books/tutorial">The Java Tutorial</A>

<P>
_______<BR>
<A NAME="TJVM"><SUP>1</SUP></A> As used on this web site, 
the terms &quot;Java virtual 
machine&quot; or &quot;JVM&quot; mean a virtual machine 
for the Java platform.


<P ALIGN="RIGHT">
<FONT SIZE="-1">[<A HREF="#top">TOP</A>]</FONT>

</FONT>
</TD>
</TR>
</TABLE>




<!-- ================ -->
<!-- End Main Content -->
<!-- ================ -->

</FONT>
</TD>
</TR>
</TABLE>

<!-- Copyright Insert -->

<BR CLEAR="ALL">

<FORM ACTION="/cgi-bin/search.cgi" METHOD="POST">
<TABLE WIDTH="100%" CELLPADDING="0" BORDER="0" CELLSPACING="5">   
  <TR>
    <TD VALIGN="BOTTOM">


</TD>
</TR>
<A HREF="/servlet/PrintPageServlet"><IMG SRC="/images/printbutton.gif" WIDTH="155" HEIGHT="25" ALT="Print Button" BORDER="0"></A>
	
    <CENTER>
    <FONT SIZE="-1" COLOR="#999999" FACE="Verdana, Arial, Helvetica, sans-serif">
    [ This page was updated: <!-- new date --> 31-Mar-2000 ]
</font></CENTER>
    </TD>
  </TR>
  
  <TR>
    <TD BGCOLOR="#CCCCCC">
    <IMG SRC="/images/pixel.gif" HEIGHT="1" WIDTH="1" ALT=""></TD>
  </TR>
  
  <TR>
    <TD>
    <CENTER>
    <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
    <A HREF="http://java.sun.com/products/">Products &amp; APIs</A> | 
    <A HREF="/developer/index.html">Developer Connection</A> | 
    <A HREF="/developer/infodocs/index.shtml">Docs &amp; Training</A> | 
    <A HREF="/developer/support/index.html">Online Support</A><BR>
    <A HREF="/developer/community/index.html">Community Discussion</A> |
    <A HREF="http://java.sun.com/industry/">Industry News</A> | 
    <A HREF="http://java.sun.com/solutions">Solutions Marketplace</A> | 
    <A HREF="http://java.sun.com/casestudies">Case Studies</A>
    </FONT>
    </CENTER>
    </TD>
  </TR>
  
  <TR>
    <TD BGCOLOR="#CCCCCC">
    <IMG SRC="/images/pixel.gif" HEIGHT="1" WIDTH="1" ALT=""></TD>
  </TR>

  <TR>
    <TD ALIGN="CENTER">
    <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
    <A HREF="http://java.sun.com/docs/glossary.html">Glossary</A> - 
    <A HREF="http://java.sun.com/applets/">Applets</A> - 
    <A HREF="http://java.sun.com/docs/books/tutorial/">Tutorial</A> - 
    <A HREF="http://java.sun.com/jobs/">Employment</A> - 
    <A HREF="http://java.sun.com/nav/business/">Business &amp; Licensing</A> - 
    <A HREF="http://java.sun.com/javastore/">Java Store</A> -
    <A HREF="http://java.sun.com/casestudies/">Java in the Real World</A>
    </FONT>
    </TD>
  </TR>

  <TR>
    <TD>
    <CENTER>
    <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
    <a href="/siteinfo/faq.html">FAQ</a> |
    <a href="/feedback/index.html">Feedback</a> | 
    <a href="http://www.dynamicdiagrams.net/mapa/cgi-bin/help.tcl?db=javasoft&dest=http://java.sun.com/">Map</a> | 
    <A HREF="http://java.sun.com/a-z/index.html">A-Z Index</A>
    </FONT>
    </CENTER>

    </TD>
  </TR>
  
  <TR>
    <TD>

    <TABLE WIDTH="100%" CELLPADDING="0" BORDER="0" CELLSPACING="0">
      <TR>
        <TD WIDTH="50%">
        <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
        For more information on Java technology<BR>
        and other software from Sun Microsystems, call:<BR>
        </FONT>
        <FONT SIZE="-1" FACE="Verdana, Arial, Helvetica, sans-serif">
        [phone]<BR></FONT>
        <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
        Outside the U.S. and Canada, dial your country's 
        <A HREF="http://www.att.com/business_traveler/attdirecttollfree/">AT&amp;T&nbsp;Direct&nbsp;Access&nbsp;Number</A> first.<BR>
        </FONT>
        </TD>

        <TD ALIGN="RIGHT" WIDTH="50%">
        <A HREF="http://www.sun.com"><IMG SRC="/images/lgsun.gif" width="64" height="30" border="0" ALT="Sun Microsystems, Inc."></A><BR>
        <FONT SIZE="-2" FACE="Verdana, Arial, Helvetica, sans-serif">
        Copyright &copy; 1995-2000
        <A HREF="http://www.sun.com">Sun Microsystems, Inc.</A><BR>
        All Rights Reserved. 
        <A HREF="http://www.sun.com/share/text/termsofuse.html">Terms of Use</A>. 
        <A HREF="http://www.sun.com/privacy/">Privacy&nbsp;Policy</A>.
        </FONT>
        </TD>
      </TR>
    </TABLE>
	
    </TD>
  </TR> 
</TABLE>
</FORM>

<!-- End Copyright Insert -->


</BODY>
</HTML>