当我学习how to use JNDI resources in Tomcat 7时,已经制作了一个名为MyBeanFactory
的自定义bean工厂。它为我的Web应用程序提供外部资源。在第一次,我们假设它提供当前系统时间戳。
然而,我意识到MyBeanFactory
在第一次请求时只被调用一次。似乎第一次执行后,java bean MyBean
已存储在Tomcat中。然后每个请求都会重用MyBean
。无论何时在浏览器中保留URL,响应始终显示与第一个相同的时间戳。以下是可能有用的元素列表:
MyBeanFactory
javax.naming.spi.ObjectFactory
有人可以告诉我为什么MyBeanFactory
只被调用一次,是否可以更改此功能?因为我需要修改工厂以在服务器中与另一个进程建立套接字。见How to serve a socket from a Java EE application?
为myBean
public class MyBean {
private String foo = "Default Foo";
private long bar = 0;
public String getFoo() { return (this.foo); }
public void setFoo(String foo) { this.foo = foo; }
public long getBar() { return (this.bar); }
public void setBar(long bar) { this.bar = bar; }
}
MyBeanFactory
public class MyBeanFactory implements ObjectFactory {
@Override
public Object getObjectInstance(Object obj, Name name, Context nameCtx,
Hashtable<?, ?> environment) throws NamingException {
System.out.println("MyBeanFactory starts");
MyBean bean = new MyBean();
bean.setBar(System.currentTimeMillis());
// Return the customized instance
return bean;
}
}
context.xml中
<?xml version="1.0" encoding="UTF-8"?>
<Context
path="/jndi"
reloadable="true"
cachingAllowed="false"
antiResourceLocking="true">
<Resource
name="bean/MyBeanFactory"
auth="Container"
type="com.mycompany.MyBean"
factory="com.mycompany.MyBeanFactory"
bar="23"/>
</Context>
的web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID"
version="3.1">
<display-name>jndi</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>com.mycompany.MyAction</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.action</url-pattern>
</servlet-mapping>
<!--
Apache Tomcat 7: JNDI Resources HOW-TO
https://tomcat.apache.org/tomcat-7.0-doc/jndi-resources-howto.html
-->
<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>
</web-app>
MyAction
public class MyAction extends HttpServlet {
// ...
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("doGet");
response.getWriter()
.append("Hello coming from ")
.append(request.getRequestURI());
Context initCtx = null;
try {
System.out.println("initCtx");
initCtx = new InitialContext();
} catch (NamingException e) {
e.printStackTrace();
}
Context envCtx = null;
try {
System.out.println("envCtx");
envCtx = (Context) initCtx.lookup("java:comp/env");
} catch (NamingException e) {
e.printStackTrace();
}
MyBean bean;
try {
System.out.println("lookup");
bean = (MyBean) envCtx.lookup("bean/MyBeanFactory");
response.getWriter()
.append("foo = " + bean.getFoo() + ", ")
.append("bar = " + bean.getBar() + ";");
} catch (NamingException e) {
e.printStackTrace();
}
System.out.println("------");
}
}
控制台
Dec 28, 2015 7:41:03 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 412 ms
doGet
initCtx
envCtx
lookup
MyBeanFactory starts // called only once
------
doGet
initCtx
envCtx
lookup
------
doGet
initCtx
envCtx
lookup
------
答案 0 :(得分:2)
您提供的<Resource>
元素具有documented by Tomcat 8以外的属性,特别是&#34; factory&#34; &&#34; bar&#34;。但是,可能会从文档中错误地省略前一个属性,因为有些示例使用它。
无论如何,我想提请你注意&#34; singleton&#34;属性。当该属性的值为true
(默认值)时,资源将被视为单例,其中单个实例由上下文维护并在所有用户之间共享。这似乎是您描述的行为。如果将该属性添加到声明中,值为false
,则该资源的每次查找都应检索一个新实例。