未解决的编译问题： java.lang.String 类型无法解析。隐式构造函数 Object() 未定义

Question

我在 Eclipse Java EE IDE（Luna Release 2 (4.4.2) 和 Java jre1.8.0_66）中创建了一个 Java 类。

package com.luv2code.jsf.hello;
 import javax.faces.bean.ManagedBean;



 @ManagedBean
 public class Student {


     private String sfirstName;
     private String slastName;

     // create a no-arg constructor
     public Student() {

     }

     public String getFirstName() {
         return sfirstName;
     }

     public void setFirstName(String sfirstName) {
         this.sfirstName = sfirstName;
     }

     public String getLastName() {
         return slastName;
     }

     public void setLastName(String slastName) {
         this.slastName = slastName;
     }

     // define public getter and setter methods to expose properties of the managed Bean

 }

我得到的错误是：

HTTP Status 500- Unresolved compilation problems
type Exception report
message unresolved compilation problem
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Unresolved compilation problems: 
 The type java.lang.String cannot be resolved. It is indirectly referenced from required .class files
 String cannot be resolved to a type
 String cannot be resolved to a type
 Implicit super constructor Object() is undefined. Must explicitly invoke another constructor
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type

 javax.faces.webapp.FacesServlet.service(FacesServlet.java:659)
 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause
java.lang.Error: Unresolved compilation problems: 
 The type java.lang.String cannot be resolved. It is indirectly referenced from required .class files
 String cannot be resolved to a type
 String cannot be resolved to a type
 Implicit super constructor Object() is undefined. Must explicitly invoke another constructor
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type
 String cannot be resolved to a type

 com.luv2code.jsf.hello.Student.<init>(Student.java:1)r





com.luv2code.jsf.hello.Student.<init>(Student.java:1)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
 sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
 java.lang.reflect.Constructor.newInstance(Unknown Source)
 java.lang.Class.newInstance(Unknown Source)
 com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:186)
 com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:100)
 com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409)
 com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269)
 com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:244)
 com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:116)
 com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
 com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
 org.apache.el.parser.AstIdentifier.getValue(AstIdentifier.java:80)
 org.apache.el.parser.AstValue.getValue(AstValue.java:137)
 org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:184)
 com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
 javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
 javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
 javax.faces.component.UIOutput.getValue(UIOutput.java:174)
 javax.faces.component.UIInput.getValue(UIInput.java:291)
 com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getValue(HtmlBasicInputRenderer.java:205)
 com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.getCurrentValue(HtmlBasicRenderer.java:355)
 com.sun.faces.renderkit.html_basic.HtmlBasicRenderer.encodeEnd(HtmlBasicRenderer.java:164)
 javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:924)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1863)
 javax.faces.render.Renderer.encodeChildren(Renderer.java:176)
 javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:894)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1856)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
 javax.faces.component.UIComponent.encodeAll(UIComponent.java:1859)
 com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:443)
 com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
 com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:120)
 com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
 com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:219)
 javax.faces.webapp.FacesServlet.service(FacesServlet.java:647)
 org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

如果我将鼠标悬停在字符串上，我会看到

字符串无法解析为类型

如果我将鼠标悬停在 Student（无参数构造函数）上，我会看到：

隐式构造函数 Object() 未定义。必须显式调用另一个构造函数。

我不确定为什么它不允许我在 m Student 类中使用私有字符串。 谁能解释一下或者给我一些建议？

Answer 1

我建议阅读有关 JSF 的教程。因为你的JSF基础好像有问题！

现在回到你的问题：

1. Student 类应该是 DataModel 类而不是 managedBean 类
2. 根据您在 web.xml 中对 FacesServlet 模式的配置，您应该运行应用程序而不是单个文件。启动容器（Tomcat）后，调用您项目的 url：即 localhost:8080/Testing/faces/test.xhtml
3. 在你的 xhtml 中有一个语法错误：<:inputText value="#{student.slastName}" />，它应该以 <h:... 开头
4. 托管 bean 应该有一个范围（applicationScoped、SessionScoped、ViewScoped、...等），但您没有在 bean 中声明它
5. managedBean 的私有字段应该有 getter/setter，只有 public 可以从外部访问（在 view/xhtml 内）

这里是一个例子：

数据模型类：

package a.b.model;

import java.io.Serializable;

public class Student implements Serializable{
    private static final long serialVersionUID = -7013884476678061379L;
    private String firstName;
    private String lastName;

    public Student() {

    }

    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }    
}

ManagedBean：

package a.b.controler;

import java.io.Serializable;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.event.AjaxBehaviorEvent;
import a.b.model.Student;

@ManagedBean
@SessionScoped
public class StudentManager implements Serializable {
    private static final long serialVersionUID = -6254452297683880945L;
    private Student student;    
    public StudentManager(){

    }   
    @PostConstruct
    public void init(){
        System.out.println("Called once on Object init!");
        this.student = new Student();
    }
    public final void save (AjaxBehaviorEvent event){
        System.out.println("Ajax command ....");
        System.out.println("Firstname: "+this.getStudent().getFirstName());
        System.out.println("Lasttname: "+this.getStudent().getLastName());
    }

    public Student getStudent() {
        return student;
    }
    public void setStudent(Student student) {
        this.student = student;
    }
}

web.xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>Testing</display-name>
  <servlet>
    <servlet-name>Faces Servlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>/faces/*</url-pattern>
  </servlet-mapping>
  <context-param>
    <param-name>javax.servlet.jsp.jstl.fmt.localizationContext</param-name>
    <param-value>resources.application</param-value>
  </context-param>
</web-app>

视图test.xhtml：

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html">
<h:head>
    <meta charset="UTF-8" />
    <title>Student Registration</title>
</h:head>
<body>
    <h:form>
             First Name: <h:inputText value="#{studentManager.student.firstName}" />
        <br />
        <br />
             Last Name: <h:inputText value="#{studentManager.student.lastName}" />
        <br />
        <br />
        <h:commandButton value="Submit">
        <f:ajax execute="@form" listener="#{studentManager.save}"/>
        </h:commandButton>
    </h:form>
</body>
</html>

启动Container(Tomcat)后，在浏览器中这样打开：

http://localhost:8080/Testing/faces/test.xhtml