tomcat中使用JNDI

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Tomacat中使用JNDI

一、JavaBean

Generic JavaBean Resources

0. Introduction 　　This resource factory can be used to create objects of any Java class that conforms to standard JavaBeans naming conventions (i.e. it has a zero-arguments constructor, and has property setters that conform to the setFoo() naming pattern. The resource factory will create a new instance of the appropriate bean class every time a lookup() for this entry is made. 　　The steps required to use this facility are described below. 1. Create Your JavaBean Class 　　Create the JavaBean class which will be instantiated each time that the resource factory is looked up. For this example, assume you create a class com.mycompany.MyBean, which looks like this: package com.mycompany; public class MyBean { private String foo = "Default Foo"; public String getFoo() { return (this.foo); } public void setFoo(String foo) { this.foo = foo; } private int bar = 0; public int getBar() { return (this.bar); } public void setBar(int bar) { this.bar = bar; } } 2. Declare Your Resource Requirements 　　Next, modify your web application deployment descriptor (/WEB-INF/web.xml) to declare the JNDI name under which you will request new instances of this bean. The simplest approach is to use a <resource-env-ref> element, like this: <resource-env-ref> <description> Object factory for MyBean instances. </description> <resource-env-ref-name> bean/MyBeanFactory </resource-env-ref-name> <resource-env-ref-type> com.mycompany.MyBean </resource-env-ref-type> </resource-env-ref> 　　WARNING - Be sure you respect the element ordering that is required by the DTD for web application deployment descriptors! See the Servlet Specification for details. 3. Code Your Application's Use Of This Resource 　　A typical use of this resource environment reference might look like this: Context initCtx = new InitialContext(); Context envCtx = (Context) initCtx.lookup("java:comp/env"); MyBean bean = (MyBean) envCtx.lookup("bean/MyBeanFactory"); writer.println("foo = " + bean.getFoo() + ", bar = " + bean.getBar()); 4. Configure Tomcat's Resource Factory 　　To configure Tomcat's resource factory, add an element like this to the <Context> element for this web application. <Context ...> ... <Resource name="bean/MyBeanFactory" auth="Container" type="com.mycompany.MyBean" factory="org.apache.naming.factory.BeanFactory" bar="23"/> ... </Context> 　　Note that the resource name (here, bean/MyBeanFactory must match the value specified in the web application deployment descriptor. We are also initializing the value of the bar property, which will cause setBar(23) to be called before the new bean is returned. Because we are not initializing the foo property (although we could have), the bean will contain whatever default value is set up by its constructor.

二、数据源：

JDBC Data Sources

0. Introduction 　　Many web applications need to access a database via a JDBC driver, to support the functionality required by that application. The J2EE Platform Specification requires J2EE Application Servers to make available a DataSource implementation (that is, a connection pool for JDBC connections) for this purpose. Tomcat 6 offers exactly the same support, so that database-based applications you develop on Tomcat using this service will run unchanged on any J2EE server. 　　For information about JDBC, you should consult the following: http://java.sun.com/products/jdbc/ - Home page for information about Java Database Connectivity. http://java.sun.com/j2se/1.3/docs/guide/jdbc/spec2/jdbc2.1.frame.html - The JDBC 2.1 API Specification. http://java.sun.com/products/jdbc/jdbc20.stdext.pdf - The JDBC 2.0 Standard Extension API (including the javax.sql.DataSource API). This package is now known as the "JDBC Optional Package". http://java.sun.com/j2ee/download.html - The J2EE Platform Specification (covers the JDBC facilities that all J2EE platforms must provide to applications). 　　NOTE - The default data source support in Tomcat is based on the DBCP connection pool from the Commons project. However, it is possible to use any other connection pool that implements javax.sql.DataSource, by writing your own custom resource factory, as described below. 1. Install Your JDBC Driver 　　Use of the JDBC Data Sources JNDI Resource Factory requires that you make an appropriate JDBC driver available to both Tomcat internal classes and to your web application. This is most easily accomplished by installing the driver's JAR file(s) into the $CATALINA_HOME/lib directory, which makes the driver available both to the resource factory and to your application. 2. Declare Your Resource Requirements 　　Next, modify the web application deployment descriptor (/WEB-INF/web.xml) to declare the JNDI name under which you will look up preconfigured data source. By convention, all such names should resolve to the jdbc subcontext (relative to the standard java:comp/env naming context that is the root of all provided resource factories. A typical web.xml entry might look like this: <resource-ref> <description> Resource reference to a factory for java.sql.Connection instances that may be used for talking to a particular database that is configured in the <Context> configurartion for the web application. </description> <res-ref-name> jdbc/EmployeeDB </res-ref-name> <res-type> javax.sql.DataSource </res-type> <res-auth> Container </res-auth> </resource-ref> 　　WARNING - Be sure you respect the element ordering that is required by the DTD for web application deployment descriptors! See the Servlet Specification for details. 3. Code Your Application's Use Of This Resource 　　A typical use of this resource reference might look like this: Context initCtx = new InitialContext(); Context envCtx = (Context) initCtx.lookup("java:comp/env"); DataSource ds = (DataSource) envCtx.lookup("jdbc/EmployeeDB"); Connection conn = ds.getConnection(); ... use this connection to access the database ... conn.close(); 　　Note that the application uses the same resource reference name that was declared in the web application deployment descriptor. This is matched up against the resource factory that is configured in the <Context> element for the web application as described below. 4. Configure Tomcat's Resource Factory 　　To configure Tomcat's resource factory, add an element like this to the <Context> element for the web application. <Context ...> ... <Resource name="jdbc/EmployeeDB" auth="Container" type="javax.sql.DataSource" username="dbusername" password="dbpassword" driverClassName="org.hsql.jdbcDriver" url="jdbc:HypersonicSQL:database" maxActive="8" maxIdle="4"/> ... </Context> 　　Note that the resource name (here, jdbc/EmployeeDB) must match the value specified in the web application deployment descriptor. 　　This example assumes that you are using the HypersonicSQL database JDBC driver. Customize the driverClassName and driverName parameters to match your actual database's JDBC driver and connection URL. 　　The configuration properties for Tomcat's standard data source resource factory (org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory) are as follows: driverClassName - Fully qualified Java class name of the JDBC driver to be used. maxActive - The maximum number of active instances that can be allocated from this pool at the same time. maxIdle - The maximum number of connections that can sit idle in this pool at the same time. maxWait - The maximum number of milliseconds that the pool will wait (when there are no available connections) for a connection to be returned before throwing an exception. password - Database password to be passed to our JDBC driver. url - Connection URL to be passed to our JDBC driver. (For backwards compatibility, the property driverName is also recognized.) user - Database username to be passed to our JDBC driver. validationQuery - SQL query that can be used by the pool to validate connections before they are returned to the application. If specified, this query MUST be an SQL SELECT statement that returns at least one row.

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