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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* To change this template file, choose Tools | Templates
* 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 session 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!我已经尝试了很多教程和选项，但仍然无法弄清楚它到底是什么。挖掘堆栈跟踪让我发疯，我部分理解错误但不知道该怎么做，请帮忙:)
最佳答案
您的 noteSB 字段缺少可见的访问器方法。将以下 getter 和 setter 方法添加到您的 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;
}
}
引用JavaBean specification .特别是这段话:
7.1 Accessor methods
Properties are always accessed via method calls on their owning object. For readable properties there will be a getter method to read the property value. For writable properties there will be a setter method to allow the property value to be updated. Thus even when a script writer types in something such as “b.Label = foo” there is still a method call into the target object to set the property, and the target object has full programmatic control.
So properties need not just be simple data fields, they can actually be computed values. Updates may have various programmatic side effects. For example, changing a bean’s background color property might also cause the bean to be repainted with the new color.
For simple properties the accessor type signatures are:
void setFoo(PropertyType value); // simple setter PropertyType getFoo(); // simple getter
关于JAVA EE 无状态 EJB IllegalArgumentException : Can not set field，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28774739/