英文:
How to Solve this java.lang.NullPointerException Error in Java?
问题
I don't know why I am getting the null pointer error.
java.lang.NullPointerException
在 web.index.getMessage(index.java:30) 处
在 java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 处
在 java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) 处
在 java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 处
在 java.base/java.lang.reflect.Method.invoke(Method.java:566) 处
在 javax.el.ELUtil.invokeMethod(ELUtil.java:227) 处
在 javax.el.BeanELResolver.invoke(BeanELResolver.java:440) 处
在 javax.el.CompositeELResolver.invoke(CompositeELResolver.java:198) 处
在 com.sun.el.parser.AstValue.getValue(AstValue.java:110) 处
在 com.sun.el.parser.AstValue.getValue(AstValue.java:177) 处
在 com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:183) 处
在 org.jboss.weld.module.web.el.WeldValueExpression.getValue(WeldValueExpression.java:50) 处
在 com.sun.faces.facelets.el.ELText$ELTextVariable.writeText(ELText.java:216) 处
在 com.sun.faces.facelets.el.ELText$ELTextComposite.writeText(ELText.java:123) 处
在 com.sun.faces.facelets.compiler.TextInstruction.write(TextInstruction.java:44) 处
在 com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:41) 处
在 com.sun.faces.facelets.compiler.UILeaf.encodeAll(UILeaf.java:169) 处
在 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650) 处
在 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650) 处
在 com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:468) 处
在 com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170) 处
在 javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132) 处
在 com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102) 处
在 com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76) 处
在 com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199) 处
在 javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708) 处
在 javax.faces.webapp.FacesServlet.service(FacesServlet.java:451) 处
在 org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1628) 处
在 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:258) 处
在 org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160) 处
在 org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:755) 处
在 org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:575) 处
在 com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99) 处
在 org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:159) 处
在 org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:371) 处
在 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:238) 处
在 com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:520) 处
在 com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:217) 处
在 org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:182) 处
在 org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:156) 处
在 org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:218) 处
在 org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:95) 处
在 org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:260) 处
在 org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:177) 处
在 org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:109) 处
在 org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:88) 处
在 org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:53) 处
在 org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:524) 处
在 org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:89) 处
在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:94) 处
在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:33) 处
在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:114) 处
在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:569) 处
在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:549) 处
在 java.base/java.lang.Thread.run(Thread.java:834)
在包 web 中的 index.java 文件：
package web;
import ejb.EmployeeFacadeLocal;
import entities.Employee;
import javax.inject.Named;
import javax.enterprise.context.SessionScoped;
import java.io.Serializable;
import javax.ejb.EJB;
@Named(value = "index")
@SessionScoped
public class index implements Serializable {
@EJB
EmployeeFacadeLocal employee;
public index() {
}
public String getMessage() {
Employee emp = new Employee(Integer.SIZE, "XYZ");
System.out.print(emp); /* Printing Objects */
employee.create(emp);
return "Hello All";
}
}
在包 ejb 中的 EmployeeFacade.java 文件：
package ejb;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
public class EmployeeFacade {
@PersistenceContext(unitName = "TODO-5PU")
private EntityManager em;
protected EntityManager getEntityManager() {
return em;
}
}
在包 ejb 中的 AbstractFacade.java 文件：
package ejb;
import java.util.List;
import javax.persistence.EntityManager;
public abstract class AbstractFacade<T> {
private Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
System.out.print(entity);
getEntityManager().persist(entity);
}
}
在包 ejb 中的 EmployeeFacadeLocal.java 文件：
package ejb;
import entities.Employee
<details>
<summary>英文:</summary>
I dont know why i am getting the null pointer error .
java.lang.NullPointerException
at web.index.getMessage(index.java:30)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at javax.el.ELUtil.invokeMethod(ELUtil.java:227)
at javax.el.BeanELResolver.invoke(BeanELResolver.java:440)
at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:198)
at com.sun.el.parser.AstValue.getValue(AstValue.java:110)
at com.sun.el.parser.AstValue.getValue(AstValue.java:177)
at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:183)
at org.jboss.weld.module.web.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at com.sun.faces.facelets.el.ELText$ELTextVariable.writeText(ELText.java:216)
at com.sun.faces.facelets.el.ELText$ELTextComposite.writeText(ELText.java:123)
at com.sun.faces.facelets.compiler.TextInstruction.write(TextInstruction.java:44)
at com.sun.faces.facelets.compiler.UIInstructions.encodeBegin(UIInstructions.java:41)
at com.sun.faces.facelets.compiler.UILeaf.encodeAll(UILeaf.java:169)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:468)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170)
at javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199)
at javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:451)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1628)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:258)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:755)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:575)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:159)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:371)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:238)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:520)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:217)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:182)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:156)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:218)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:95)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:260)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:177)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:109)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:88)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:53)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:524)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:89)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:94)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:33)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:114)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:569)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:549)
at java.base/java.lang.Thread.run(Thread.java:834)
package web;
import ejb.EmployeeFacadeLocal;
import entities.Employee;
import javax.inject.Named;
import javax.enterprise.context.SessionScoped;
import java.io.Serializable;
import javax.ejb.EJB;
@Named(value = "index")
@SessionScoped
public class index implements Serializable {
@EJB
EmployeeFacadeLocal employee;
public index() {
}
public String getMessage(){
Employee emp = new Employee(Integer.SIZE,"XYZ");
System.out.print(emp) */ Printing Objects */
employee.create(emp);
return "Hello All";
}
}
package ejb;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
public class EmployeeFacade {
@PersistenceContext(unitName = "TODO-5PU")
private EntityManager em;
@override
protected EntityManager getEntityManager() {
return em;
}
}
package ejb;
import java.util.List;
import javax.persistence.EntityManager;
public abstract class AbstractFacade<T> {
private Class<T> entityClass;
public AbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
System.out.print(entity);
getEntityManager().persist(entity);
}
}
package ejb;
import entities.Employee;
import java.util.List;
import javax.ejb.Local;**strong text**
@Local
public interface EmployeeFacadeLocal {
void create(Employee employee);
}
package entities;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.validation.constraints.Size;
import javax.xml.bind.annotation.XmlRootElement;
@Entity
@Table(name = "employee")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Employee.findAll", query = "SELECT e FROM Employee e"),
@NamedQuery(name = "Employee.findById", query = "SELECT e FROM Employee e WHERE e.id = :id"),
@NamedQuery(name = "Employee.findByName", query = "SELECT e FROM Employee e WHERE e.name = :name")})
public class Employee implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "ID")
private Integer id;
@Size(max = 255)
@Column(name = "NAME")
private String name;
public Employee() {
}
public Employee(Integer id , String name) {
this.id = id;
this.name = name;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}
@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Employee)) {
return false;
}
Employee other = (Employee) 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 "entities.Employee[ id=" + id + "]";
}
}
</details>
# 答案1
**得分**: 2
"getMessage"在第30行接收到一个"null"值。检查这个值来自哪里，你应该能够找到问题的原因。
<details>
<summary>英文:</summary>
The "getMessage" at line 30 receives a "null" value. Check from where that values comes and you should be able to pinpoint your problem.
</details>
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