當我在學習how to use JNDI resources in Tomcat 7時,已經建立了一個自定義的bean工廠,名爲MyBeanFactory
。它爲我的Web應用程序提供外部資源。我們第一次假設它提供了當前的系統時間戳。爲什麼JNDI資源只能在Tomcat中調用一次?
但是,我意識到MyBeanFactory
僅在第一次請求時才被調用一次。在第一次執行後,似乎javabean MyBean
已經存儲在Tomcat中。然後MyBean
被每個請求重用。無論何時我在瀏覽器中保存URL,響應總是顯示與第一個相同的時間戳。我這裏還有元素的列表,可以幫助:
- 爲myBean:由
MyBeanFactory
- MyBeanFactory提供的豆:工廠實施
javax.naming.spi.ObjectFactory
- 的context.xml:上下文描述符資源,位於META-INF文件夾中
- web.xml:部署描述符
- MyAction:在HTTP Servlet中
- 控制檯
有人能告訴我爲什麼MyBeanFactory
只調用一次,如果它有可能改變這個功能嗎?因爲我需要修改工廠來建立與服務器中的另一個進程的套接字。見How to serve a socket from a Java EE application?
爲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;
}
}
的context.xml
<?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("------");
}
}
控制檯
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
------
由於您正在定義一個servlet上下文資源,因此期望給定的上下文將只有一個實例似乎是合理的。上下文資源的全部要點是要共享的。這就是說,通過引用Tomcat 7,您已經拋棄了我,但使用了該版本的Tomcat沒有記錄的配置屬性。你實際使用哪個版本? –
@JohnBollinger我使用的是tomcat 8.0.21 –