關於JBoss運行ejb
利用JBOSS+MyEclipse完成一個簡單的EJB示例
目標:
1、編寫一個簡單的無狀態會話Bean,傳入一個字符串參數,返回字符串Hello + 字符串參數。
2、通過JSP頁面上輸入一個字符串,提交到Servlet,並調用EJB,最後在一個頁面上輸出處理後的字符串。
工具:
JBOSS 4.2GA + Eclipse 3.2.2 +MyEclipse 5.5GA + JDK 1.6
首先需要搭建好各種環境,這一步比較簡單,就不再贅述。唯一需要注意的是在啓動JBOSS服務器時可能會出現一些問題。如端口號被佔用而導致服務器無法啓動。如果出現這個問題可以在%JBOSS%/server/default/deploy/jboss-web.deployer/目錄下找到server.xml文件,修改<Connector port="8080" address="${jboss.bind.address}"
maxThreads="250" maxHttpHeaderSize="8192"
emptySessionPath="true" protocol="HTTP/1.1"
enableLookups="false" redirectPort="8443" acceptCount="100"
connectionTimeout="20000" disableUploadTimeout="true" />
中的port屬性,然後再重新啓動服務器。默認端口是8080。
JBOSS自帶了TOMCAT 5.X,當然也可以使用另外的Web服務器,不過後面的程序會稍微有些改動。
環境搭建完成後就需要編寫EJB代碼。一個EJB至少需要3個類,即Home接口、遠程接口、實現類。新建一個EJB Project,項目名爲:MyFirstEJB.
1、創建Home接口---HelloHome.java
package com.lovo.interfaces;
public interface HelloHome extends javax.ejb.EJBHome {
public com.lovo.interfaces.Hello create() throws javax.ejb.CreateException,
java.rmi.RemoteException;
}
2、創建遠程接口---Hello.java
package com.lovo.interfaces;
public interface Hello extends javax.ejb.EJBObject {
public String sayHello(String message) throws java.rmi.RemoteException;
}
3、創建實現類---HelloBean.java
package com.lovo.ejb;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBException;
import javax.ejb.SessionBean;
import javax.ejb.SessionContext;
public class HelloBean implements SessionBean {
private SessionContext context;
public HelloBean() {}
public void ejbActivate() throws EJBException, RemoteException {}
public void ejbPassivate() throws EJBException, RemoteException {}
public void ejbRemove() throws EJBException, RemoteException {}
public void ejbCreate() throws CreateException {}
public void setSessionContext(SessionContext newContext)
throws EJBException {
this.context = newContext;
}
public String sayHello(String message){
if(message == null)
message = "";
message = "Hello " + message + "!";
return message;
}
}
其中方法sayHello就是我們需要實現的業務。
類建好之後,接下來就需要配置相關的xml文件。在該項目下的META-INF裏新建兩個xml文件ejb-jar.xml和jboss.xml。具體配置如下:
ejb-jar.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">
<ejb-jar>
<description>
<![CDATA[No Description.]]>
</description>
<display-name>Generated by XDoclet</display-name>
<enterprise-beans>
<session>
<description>
<![CDATA[Description for Hello]]>
</description>
<display-name>Name for Hello</display-name>
<ejb-name>Hello</ejb-name>
<home>com.lovo.interfaces.HelloHome</home>
<remote>com.lovo.interfaces.Hello</remote>
<ejb-class>com.lovo.ejb.HelloBean</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Container</transaction-type>
</session>
</enterprise-beans>
<assembly-descriptor>
</assembly-descriptor>
</ejb-jar>
jboss.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jboss PUBLIC "-//JBoss//DTD JBOSS 2.4//EN" "http://www.jboss.org/j2ee/dtd/jboss_2_4.dtd">
<jboss>
<enterprise-beans>
<session>
<ejb-name>Hello</ejb-name>
<jndi-name>ejb/Hello</jndi-name>
</session>
</enterprise-beans>
<resource-managers>
</resource-managers>
</jboss>
使用XDoclet來自動生成這些文件還是很方便的,只是同時會生成一些多餘的類和代碼,需要手動去刪除他們。
到這裏一個簡單的無狀態會話Bean就完成了,下面就是將他們部署到Jboss下面。可以將項目打包成jar文件,然後放在
%JBOSS%/server/default/deploy/目錄下,這樣就算部署完成。還可以使用MyEclipse來幫你進行部署。如果控制檯上出現:
01:59:48,640 INFO [EjbModule] Deploying Hello
01:59:48,703 INFO [ProxyFactory] Bound EJB Home 'Hello' to jndi 'ejb/Hello'
01:59:48,703 INFO [EJBDeployer] Deployed: file:/%jboss%/server/default/deploy/MyFirstEJB.jar/
就表示部署成功。下面我們就可以編寫客戶端程序來調用該EJB。
新建一個Web項目,項目名爲testEJB,裏面包含兩個jsp文件和一個servlet。
EJBServlet.java
package com.lovo.servlet;
import java.io.IOException;
import javax.ejb.CreateException;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.lovo.interfaces.Hello;
import com.lovo.interfaces.HelloHome;
public class EJBServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("gb2312");
String info = request.getParameter("info");
InitialContext context = null;
Hello hello = null;
try
{
context = new InitialContext();
HelloHome home = (HelloHome)context.lookup("ejb/Hello");
hello = home.create();
}
catch (NamingException e)
{
e.printStackTrace();
}
catch (CreateException e)
{
e.printStackTrace();
}
info = hello.sayHello(info);
request.setAttribute("info", info);
request.getRequestDispatcher("message.jsp").forward(request, response);
}
}
從jsp頁面上獲得表單中的字符串,然後將這個字符串傳遞到EJB的會話Bean中進行處理。最後將返回的字符串顯示在另外一個JSP頁面上。
index.jsp
<%@ page language="java" isELIgnored="false" pageEncoding="gb2312"%>
<html>
<head>
<title>EJB</title>
</head>
<body>
<form action="servlet" method="post">
<input type="text" name="info" />
<input type="submit" value="提交">
</form>
</body>
</html>
message.jsp
<%@ page language="java" isELIgnored="false" pageEncoding="utf-8"%>
<html>
<head>
<title>message</title>
</head>
<body>
<h1>${info }</h1>
</body>
</html>
如果Web項目和EJB項目在同一服務器中,那麼象上面的程序運行是沒什麼問題的。如果Web項目和EJB項目不在同一臺服務器中,或者同一臺服務器中使用的不是JBOSS自帶的Tomcat,那麼需要修改一下servlet:
修改後的EJBServlet.java
package com.lovo.servlet;
import java.io.IOException;
import java.util.Hashtable;
import javax.ejb.CreateException;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.lovo.interfaces.Hello;
import com.lovo.interfaces.HelloHome;
public class EJBServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("gb2312");
String info = request.getParameter("info");
InitialContext context = null;
Hello hello = null;
/*********************添加的代碼*****************************/
Hashtable environment = new Hashtable();
environment.put(Context.INITIAL_CONTEXT_FACTORY,
"org.jnp.interfaces.NamingContextFactory");
environment.put(Context.URL_PKG_PREFIXES,
"org.jboss.naming:org.jnp.interfaces");
environment.put(Context.PROVIDER_URL, "jnp://localhost:1099");
/***********************************************************/
try
{
context = new InitialContext(environment);
HelloHome home = (HelloHome) context.lookup("ejb/Hello");
hello = home.create();
}
catch (NamingException e)
{
e.printStackTrace();
}
catch (CreateException e)
{
e.printStackTrace();
}
info = hello.sayHello(info);
request.setAttribute("info", info);
request.getRequestDispatcher("message.jsp").forward(request, response);
}
}
光修改這裏還不夠,還需要將%jboss%/client/jbossall-client.jar 和EJB項目的jar包拷貝到web 項目中WEB-INF/lib目錄下。
補充:在jsp或servlet中調用EJB時出現下面錯誤時:
04:03:33,714 INFO [STDOUT] java.rmi.ServerException: EJBException:; nested exception is:
javax.ejb.EJBException: Invalid invocation, check your deployment packaging, method=public abstract test.ejb.TestEJBInterface test.ejb.TestEJBHome.create() throws javax.ejb.CreateException,java.rmi.RemoteException
解決辦法有三種:
1、編輯%jboss%/server/default/conf/jboss-service.xml
<mbean code="org.jboss.naming.NamingService"
name="jboss:service=Naming"
xmbean-dd="resource:xmdesc/NamingService-xmbean.xml">
<!-- The call by value mode. true if all lookups are unmarshalled using
the caller's TCL, false if in VM lookups return the value by reference.
-->
<attribute name="CallByValue">false</attribute>
...
</mbean>
將屬性CallByValue的值改爲true
2、編輯%jboss%/server/default/deploy/ear-deployer.xml
<mbean code="org.jboss.deployment.EARDeployer"
name="jboss.j2ee:service=EARDeployer">
<attribute name="Isolated">false</attribute>
<attribute name="CallByValue">false</attribute>
<attribute name="EnablelibDirectoryByDefault">true</attribute>
</mbean>
將屬性Isolated和CallByValue的值改爲true
3、編輯%jboss%/server/default/deploy/jboss-web.deployer/META-INF/jboss-service.xml
<attribute name="Java2ClassLoadingCompliance">false</attribute>
<attribute name="UseJBossWebLoader">false</attribute>
將屬性Java2ClassLoadingCompliance和UseJBossWebLoader的值改爲false,這裏默認值一般都是false
一般情況下,使用第二種方式就可以解決該問題。
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