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JNDI(Java 命名和目录接口)(三)---- Tomcat中配置和使用JNDI

2009-01-23 16:38 1186 查看
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]);

}

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]));

}

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

最后打开浏览器,访问 http://localhost:8080/DBTest/ViewTable.jsp就可以看到结果
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