Question

当我尝试在Java EE应用程序中触发事件时，我得到一个空指针异常。下面是代码。

HelloEvent事件模型：

package com.eventhandling;

import java.io.Serializable;
import java.util.logging.Logger;


public class HelloEvent implements Serializable {
    private static final long serialVersionUID = 1L;
    private String message;
    private static Logger LOGGER=Logger.getLogger("Log");
    public HelloEvent() {
    }

    public HelloEvent(String message) {
        this.message = message;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "helloEvent toString";
    }


}

HelloMessenger托管bean：

package com.eventhandling;

import java.util.logging.Logger;

import javax.annotation.PostConstruct;
import javax.enterprise.event.Event;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.inject.Inject;


@ManagedBean(name = "messenger")
@SessionScoped
public class HelloMessenger {

    @Inject
    Event<HelloEvent> events;
    private static Logger LOGGER = Logger.getLogger("Log");

    public void hello() {
        LOGGER.info("hello called");
        LOGGER.info("events" + events);
        HelloEvent helloEvent= new HelloEvent("testEvent");
        LOGGER.info("helloEvent"+helloEvent);
        events.fire(helloEvent);

    }

}

HelloListener事件监听器：

package com.eventhandling;

import javax.enterprise.event.Observes;
import javax.faces.bean.SessionScoped;

@SessionScoped
public class HelloListener {

    public void listenToHello(@Observes HelloEvent helloEvent) {

        System.out.println("HelloEvent: " + helloEvent);

    }

}

JSF视图Welcome.xhtml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"    
      xmlns:h="http://java.sun.com/jsf/html">

    <h:head>
        <title>JSF 2.0 Hello World</title>
    </h:head>
    <h:body bgcolor="white">
        <h3>JSF 2.0 Hello World Example - welcome.xhtml</h3>
        <h4>Welcome </h4>
        <h:form>
            <h:commandButton value="Fire Event" action="#{messenger.hello}"></h:commandButton>
        </h:form>
    </h:body>
</html>

Maven依赖项：

        <dependency>
            <groupId>com.sun.faces</groupId>
            <artifactId>jsf-api</artifactId>
            <version>2.1.7</version>
        </dependency>
        <dependency>
            <groupId>com.sun.faces</groupId>
            <artifactId>jsf-impl</artifactId>
            <version>2.1.7</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
        </dependency>
        <dependency>
            <groupId>javax.enterprise</groupId>
            <artifactId>cdi-api</artifactId>
            <version>1.0</version>
        </dependency>

当我点击命令按钮时，我得到一个NullPointerException。这是因为events属性未被注入并保持null。这是怎么造成的，我该如何解决呢？

登录Tomcat启动：

Jan 30, 2014 4:43:35 PM org.apache.catalina.core.AprLifecycleListener init
INFO: Loaded APR based Apache Tomcat Native library 1.1.27 using APR version 1.4
.6.
Jan 30, 2014 4:43:35 PM org.apache.catalina.core.AprLifecycleListener init
INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters [false], ra
ndom [true].
Jan 30, 2014 4:43:36 PM org.apache.catalina.core.AprLifecycleListener initialize
SSL
INFO: OpenSSL successfully initialized (OpenSSL 1.0.1d 5 Feb 2013)
Jan 30, 2014 4:43:37 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-apr-6080"]
Jan 30, 2014 4:43:37 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-apr-6006"]
Jan 30, 2014 4:43:37 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 3047 ms
Jan 30, 2014 4:43:37 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Jan 30, 2014 4:43:37 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.42
Jan 30, 2014 4:43:37 PM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive D:\software\testtomcat_6080-_Analytics_w
ars\apache-tomcat-7.0.42\webapps\JavaServerFaces.war
Jan 30, 2014 4:43:43 PM org.apache.catalina.loader.WebappClassLoader validateJar
File
INFO: validateJarFile(D:\software\testtomcat_6080-_Analytics_wars\apache-tomcat-
7.0.42\webapps\JavaServerFaces\WEB-INF\lib\jsp-api-2.1.jar) - jar not loaded. Se
e Servlet Spec 2.3, section 9.7.2. Offending class: javax/el/Expression.class
Jan 30, 2014 4:43:43 PM org.apache.catalina.loader.WebappClassLoader validateJar
File
INFO: validateJarFile(D:\software\testtomcat_6080-_Analytics_wars\apache-tomcat-
7.0.42\webapps\JavaServerFaces\WEB-INF\lib\servlet-api-2.5.jar) - jar not loaded
. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.cl
ass
Jan 30, 2014 4:43:46 PM com.sun.faces.config.ConfigureListener contextInitialize
d
INFO: Initializing Mojarra 2.1.7 (SNAPSHOT 20120206) for context '/JavaServerFac
es'
Jan 30, 2014 4:43:46 PM com.sun.faces.spi.InjectionProviderFactory createInstanc
e
INFO: JSF1048: PostConstruct/PreDestroy annotations present.  ManagedBeans metho
ds marked with these annotations will have said annotations processed.
Jan 30, 2014 4:43:47 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\admin
Jan 30, 2014 4:43:47 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\docs
Jan 30, 2014 4:43:47 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\examples
Jan 30, 2014 4:43:48 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\host-manager
Jan 30, 2014 4:43:48 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\manager
Jan 30, 2014 4:43:48 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory D:\software\testtomcat_6080-_Analytics
_wars\apache-tomcat-7.0.42\webapps\ROOT
Jan 30, 2014 4:43:48 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-apr-6080"]
Jan 30, 2014 4:43:48 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-apr-6006"]
Jan 30, 2014 4:43:48 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 11372 ms

Answer 1

您似乎将JSF和CDI概念混合在一个托管bean中。

使用@Named和@SessionScoped但请确保您拥有正确的@SessionScoped。应删除@ManagedBean。 javax.enterprise.context是包名。如果使用来自JSF的SessionScoped，则会发生无记录的行为。

我不确定你的依赖关系，但id取决于我猜的容器。请通过查看启动日志来验证CDI启动。确保在META-INF中有beans.xml。

您在评论中粘贴的日志没有提及Weld和OpenWebBeans，也没有提到您在pom.xml中粘贴的依赖项。我的结论是你没有正确地包括CDI。

您有什么选择？

选项1

Tomcat与OWB / Weld相处得很好但是因为OpenWebBeans与你的容器共享相同的许可证，所以我建议你相应地为这些文档添加依赖项： http://openwebbeans.apache.org/owbsetup_ee.html＆lt; ---解释您在依赖项中需要什么 http://openwebbeans.apache.org/download.html＆lt; ---解释如何添加到pom.xml

我写了那些文档，它们还不完美（sry）但它应该让你去。

选项2： 切换到tomEE并仅使用maven中提供的。这是tomEE的版本，包含您需要的所有内容。我真的很喜欢tomEE，这是我的默认推荐。邮件列表非常好，如果您有任何问题，可以立即到达。

选项3： 使用Jboss Weld并按照他们的手册开始使用Tomcat。应该很容易找到使用谷歌。

空指针javax.enterprise.event.Event的异常

1 个答案: