JNDI是J2EE中一个很重要的标准,通常我们是在EJB编程中用到, Tomcat4.0中提供了在JSP和Servelt中直接使用JNDI的方法,下面谈一下在Tomcat4.0中配置和使用JNDI的方法 (以通过JNDI连接数据库为例) 假设使用的数据库是mysql,实验例子在TOMCAT_HOME/webapps/DBTest目录中
A.将mysql的JDBC连接库mm.mysql-2.0.9-bin.jar放入TOMCAT_HOME/common/lib中
B.配置TOMCAT_HOME/conf/serer.xml文件在<Service>段中加入一个Context: <Context path="/DBTest" docBase="DBTest" debug="5" reloadable="true" crossContext="true"> </Context> 这是DBTest的根路径,这是为了在DBTest中使用做准备.
C.在上面加入的<Context>段加入 <Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource"/>
<ResourceParams name="jdbc/TestDB"> <parameter> <name>factory</name> <value>org.apache.commons.dbcp.BasicDataSourceFactory</value> </parameter>
<!-- Maximum number of dB connections in pool. Make sure you configure your mysqld max_connections large enough to handle all of your db connections. Set to 0 for no limit. --> <parameter> <name>maxActive</name> <value>100</value> </parameter>
<!-- Maximum number of idle dB connections to retain in pool. Set to 0 for no limit. --> <parameter> <name>maxIdle</name> <value>30</value> </parameter>
<!-- Maximum time to wait for a dB connection to become available in ms, in this example 10 seconds. An Exception is thrown if this timeout is exceeded. Set to -1 to wait indefinitely. --> <parameter> <name>maxWait</name> <value>10000</value> </parameter>
<!-- MySQL dB username and password for dB connections --> <parameter> <name>username</name> <value>test</value> </parameter> <parameter> <name>password</name> <value>test</value> </parameter>
<!-- Class name for mm.mysql JDBC driver --> <parameter> <name>driverClassName</name> <value>org.gjt.mm.mysql.Driver</value> </parameter>
<!-- The JDBC connection url for connecting to your MySQL dB.--> <parameter> <name>url</name> <value>jdbc:mysql://localhost:3306/test</value> </parameter> </ResourceParams>
这里每一个小段都有英文注解,是Tomcat提供的,我们可以将按照Sample加入,主要修改的是driverClassName, url,和用户帐号;需要强调的是"jdbc/TestDB"就是JDNI要查找的Name.
D. 在JSPh或servlet中使用JNDI查找服务 下面是在JSP文件中关于JNDI使用的代码(文件名记为UserHandleDB.jsp) 需要注意的是JNDI NAME要在前面加上"java:comp/env/"
<%@ page language="java"%> <%@ page import="java.util.*" %> <%@ page import="java.sql.*" %> <%@ page import="javax.sql.*" %> <%@ page import="javax.naming.*" %>
<% String jndi_name="java:comp/env/jdbc/TestDB"; String select_user_sql="select userid,name,birthday, email from emp"; String colnames[][]={{"User ID","Name","Birth day","EMail"}, {"userid","name","birthday","email"}}; Vector userSet=new Vector(); Vector columnSet=new Vector();
for(int i=0;i<colnames[0].length;i++){ columnSet.add(colnames[0][i]); } userSet.add(columnSet);
Context ctx = new InitialContext(); if(ctx == null ) throw new Exception("No Context");
DataSource ds = (DataSource)ctx.lookup(jndi_name);
Connection conn = ds.getConnection();
try { PreparedStatement psPreparedStatement=conn.prepareStatement(select_user_sql); ResultSet resultSet = psPreparedStatement.executeQuery(); while(resultSet.next()){ columnSet=new Vector(); for(int i=0;i<colnames[1].length;i++){ columnSet.add(resultSet.getString(colnames[1][i])); } userSet.add(columnSet); } }catch(SQLException e) { e.printStackTrace(); }finally { conn.close(); %>
E. 引用UserHandleDB.jsp(记为ViewTable.jsp) <html> <head> <title>Test Database </title> <body > <%@ include file="UserHandleDB.jsp" %> <table border="1" > <% for(int i=0;i<userSet.size();i++){ Vector colSet=(Vector)userSet.get(i); out.print("<tr>"); for(int j=0;j<colSet.size();j++){ String col=(String)colSet.get(j); out.print("<td>"+col+"</td>"); } out.print("</tr>"); } %> </table> </body> </html>
F. 在web.xml中加入 <resource-ref> <description>DB Connection</description> <res-ref-name>jdbc/TestDB</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> </resource-ref> 这里的jdbc/TestDb要和C中Resource段的name匹配
G. 观察结果 首先确定数据库已经启动,接着启动Tomcat,如果Tomcat启动异常,可能的原因是数据库的JDBC库没有加载 
|