我在学习ejb时遇到了一些麻烦。我想要的只是在数据库上编写一个简单的应用程序操作。这是我的代码：
Servlet - Main.java
package main;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import javax.ejb.EJB;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "Main", urlPatterns = {"/"})
public class Main extends HttpServlet {
@EJB
private NoteSB noteSB;
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
PrintWriter out = response.getWriter();
List<Note> notes = noteSB.getNotes();
for( int i=0,len=notes.size() ; i<len ; ++i ) {
out.println(notes.get(i));
}
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}
@Override
public String getServletInfo() {
return "Short description";
}
}
实体 - Note.java
/*
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* and open the template in the editor.
*/
package main;
import java.io.Serializable;
import java.security.Timestamp;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "NOTES")
public class Note implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String note;
private Timestamp date;
public Note(){}
public Note(String note, Timestamp date) {
this.note = note;
this.date = date;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@Override
public boolean equals(Object object) {
if (!(object instanceof Note)) {
return false;
}
Note other = (Note) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}
@Override
public String toString() {
return "Note["+ this.date +"]: " + this.note;
}
}
无状态会话bean - NoteSB.java
package main;
import java.util.List;
import javax.annotation.PreDestroy;
import javax.ejb.Stateless;
import javax.ejb.LocalBean;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
@Stateless
@LocalBean
public class NoteSB {
@PersistenceContext(name = "jee-warPU")
private EntityManager em;
public void newNote(Note n) {
em.persist(n);
}
public List<Note> getNotes() {
return em.createNativeQuery("SELECT * FROM NOTES").getResultList();
}
@PreDestroy
public void destroy() {
em.close();
}
}
persistance.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="jee-warPU" transaction-type="JTA">
<jta-data-source>java:comp/DefaultDataSource</jta-data-source>
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
<property name="javax.persistence.schema-generation.database.action" value="create"/>
</properties>
</persistence-unit>
</persistence>
这是我的堆栈跟踪：
Info: file:/C:/Users/BB/Documents/NetBeansProjects/jee/jee-war/build/web/WEB-INF/classes/_jee-warPU logout successful
Info: visiting unvisited references
Info: visiting unvisited references
Info: visiting unvisited references
Info: visiting unvisited references
Info: visiting unvisited references
Info: EclipseLink, version: Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd
Info: file:/C:/Users/BB/Documents/NetBeansProjects/jee/jee-war/build/web/WEB-INF/classes/_jee-warPU login successful
Info: Portable JNDI names for EJB NoteSB: [java:global/jee-war/NoteSB, java:global/jee-war/NoteSB!main.NoteSB]
WARN: WELD-000411: Observer method [BackedAnnotatedMethod] org.glassfish.sse.impl.ServerSentEventCdiExtension.processAnnotatedType(@Observes ProcessAnnotatedType<Object>, BeanManager) receives events for all annotated types. Consider restricting events using @WithAnnotations or a generic type with bounds.
WARN: WELD-000411: Observer method [BackedAnnotatedMethod] private org.glassfish.jersey.gf.cdi.internal.CdiComponentProvider.processAnnotatedType(@Observes ProcessAnnotatedType<Object>) receives events for all annotated types. Consider restricting events using @WithAnnotations or a generic type with bounds.
WARN: WELD-000411: Observer method [BackedAnnotatedMethod] public org.glassfish.jms.injection.JMSCDIExtension.processAnnotatedType(@Observes ProcessAnnotatedType<Object>) receives events for all annotated types. Consider restricting events using @WithAnnotations or a generic type with bounds.
Info: Loading application [jee-war] at [/jee-war]
Info: jee-war was successfully deployed in 783 milliseconds.
Info: WebModule[null] ServletContext.log():Marking servlet Main as unavailable
Warning: StandardWrapperValve[Main]: Allocate exception for servlet Main
java.lang.IllegalArgumentException: Can not set main.NoteSB field main.Main.noteSB to main.Main
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
at sun.reflect.UnsafeFieldAccessorImpl.ensureObj(UnsafeFieldAccessorImpl.java:58)
at sun.reflect.UnsafeObjectFieldAccessorImpl.set(UnsafeObjectFieldAccessorImpl.java:75)
at java.lang.reflect.Field.set(Field.java:758)
at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl._inject(InjectionManagerImpl.java:688)
at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.inject(InjectionManagerImpl.java:507)
at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.injectInstance(InjectionManagerImpl.java:141)
at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.injectInstance(InjectionManagerImpl.java:127)
at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.createManagedObject(InjectionManagerImpl.java:347)
at com.sun.enterprise.web.WebContainer.createServletInstance(WebContainer.java:991)
at com.sun.enterprise.web.WebModule.createServletInstance(WebModule.java:2130)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1404)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:1211)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:237)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
at java.lang.Thread.run(Thread.java:745)
我将不胜感激任何帮助！我尝试过很多教程和选项，但仍然无法弄清楚它是什么。挖掘堆栈跟踪只是让我发疯，我部分了解错误但不知道该怎么做，请帮忙:)）
答案 0 :(得分：1)
您缺少noteSB字段的可见访问方法。将以下getter和setter方法添加到Main类：
public class Main extends HttpServlet {
// all your current code here
public NoteSB getNoteSB() {
return this.noteSB;
}
public void setNoteSB(NoteSB noteSB) {
this.noteSB = noteSB;
}
}
请参阅JavaBean specification。特别是这段话：
7.1存取方法
始终通过方法调用访问属性 宾语。对于可读属性，将有一个 getter 方法 读取属性值。对于可写属性，将有一个 setter 方法允许更新属性值。因此，即使脚本编写者在那里键入诸如“b.Label = foo”之类的东西 仍然是一个方法调用目标对象来设置属性，和 目标对象具有完全的程序控制。
因此，属性不仅仅是简单的数据字段，它们实际上也是如此 是计算值。更新可能有各种程序方面 效果。例如，更改bean的背景颜色属性 也可能导致用新颜色重新绘制bean。
对于简单属性，访问者类型签名为：
void setFoo(PropertyType value); // simple setter PropertyType getFoo(); // simple getter