【发布时间】：2015-12-29 20:22:06
【问题描述】：
我在此应用程序上遇到错误，该应用程序通过 index.html 页面上的一个按钮将用户保持在 BD 上，该按钮通过单击 POST 来调用 servlet。 很长一段时间我都在努力寻找错误原因，我将不胜感激。 我认为错误应该是放一些注释的时候或者没有找到servlet。
错误：
javax.servlet.ServletException: Error instantiating servlet class servlet.TestEJB
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1517)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1474)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
root cause
javax.naming.NameNotFoundException: Name [servlet.TestEJB/meuEJB] is not bound in this Context. Unable to find [servlet.TestEJB].
org.apache.naming.NamingContext.lookup(NamingContext.java:818)
org.apache.naming.NamingContext.lookup(NamingContext.java:166)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1517)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1474)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
伺服器：
@WebServlet("/TestEJB")
public class TestEJB extends HttpServlet{
private static final long serialVersionUID = 1L;
@EJB
MissatgesEJB meuEJB;
/* (non-Javadoc)
* @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
*/
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html;charset=UTF-8");
try (PrintWriter out = resp.getWriter()) {
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet TestEJB</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Proves Whatsapp</h1>");
Usuaris usuari = new Usuaris("robert_1994", "Paucasals33", "Bruch");
out.println("Insertant Usuari... " + meuEJB.insertarUsuari(usuari) + "<br/>");
out.println("</body>");
out.println("</html>");
}
}
}
方法：
@Stateless
public class MissatgesEJB {
@PersistenceUnit
EntityManagerFactory emf;
public String insertarUsuari(Usuaris u) {
EntityManager em = emf.createEntityManager();
try {
// Excriu a la BD.
em.persist(u);
// Forçem a que escrigui ara ala BD.
em.flush();
return "ok";
} catch (Exception ex) {
return ex.getMessage();
} finally {
em.close();
}
}
}
persistence.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1"
xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="JPA-1" transaction-type="RESOURCE_LOCAL">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>beans.Historial</class>
<class>beans.Missatges</class>
<class>beans.Usuaris</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/bdwhatsapp" />
<property name="javax.persistence.jdbc.user" value="marti" />
<property name="javax.persistence.jdbc.password" value="Paucasals33" />
<property name="javax.persistence.schema-generation.database.action"
value="none" />
</properties>
</persistence-unit>
</persistence>
【问题讨论】：
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没有这个条目我得到这个错误：严重：Servlet.service() for servlet [servlet.TestEJB] in context with path [/activitat] throw exception java.lang.NullPointerException at servlet.TestEJB。 doPost(TestEJB.java:43) 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:648) 在 javax.servlet.http.HttpServlet.service(HttpServlet.java:729) 在