JBoss 7: ClassCastException: MyCustomTag 无法转换为 javax.servlet.jsp.tagext.Tag

Question

在 JBoss 服务器中部署包含自定义标记的 Web 应用程序出现以下异常：

java.lang.ClassCastException: com.test.taglib.MyCustomTag cannot be cast to javax.servlet.jsp.tagext.Tag
    at org.apache.jasper.runtime.PerThreadTagHandlerPool.get(PerThreadTagHandlerPool.java:96) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.jsp.WEB_002dINF.jsp.testAppData_jsp._jspx_meth_fx_005fsystemDate_005f0(testAppData_jsp.java:725)
    at org.apache.jsp.WEB_002dINF.jsp.testAppData_jsp._jspService(testAppData_jsp.java:150)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:69) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-1.jar:1.0.2.Final-redhat-1]
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:365) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:309) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:242) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-1.jar:1.0.2.Final-redhat-1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:832) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:620) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:553) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:482) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:669) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:574) [org.springframework.web.servlet-3.0.7.RELEASE.jar:3.0.7.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-1.jar:1.0.2.Final-redhat-1]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.2.Final-redhat-1.jar:1.0.2.Final-redhat-1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:295) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.4.8.Final-redhat-4.jar:7.4.8.Final-redhat-4]

我的自定义标签 class

public class MyCustomTag extends BodyTagSupport {

    ...
}

MyCustomTag 间接继承 Tag class：MyCustomTag -> BodyTagSupport -> BodyTag -> IterationTag -> Tag

所有标签classes被打包成jsp-api-2.1.jar并包含在module.xml中，如下图：

module.xml

<?xml version="1.0" encoding="UTF-8"?>

<module xmlns="urn:jboss:module:1.1" name="com">
    <resources>
        ...
        <resource-root path="jsp-api-2.1.jar"/>
        ...
    </resources>

    <dependencies>
        <module name="sun.jdk"/>
        <module name="javax.api"/>
        <module name="javax.servlet.api"/>
        <module name="org.jboss.logging"/>
        <module name="org.jboss.modules"/>
    </dependencies>

</module>

我在 jboss-eap-6.3 文件夹中搜索了冲突的 jar。但是，BodyTagSupport class 仅存在于 jsp-api-2.1.jar 和 jboss-jsp-api_2.2_spec-1.0.1.Final-红帽-2.jar。而且两个罐子都兼容。

那么，为什么我得到 ClassCastException？

Answer 1

在module.xml文件中添加<module name="javax.servlet.jsp.api"/>依赖后解决，如下所示：

<?xml version="1.0" encoding="UTF-8"?>

<module xmlns="urn:jboss:module:1.1" name="com">
    <resources>
        ...
        <resource-root path="jsp-api-2.1.jar"/>
        ...
    </resources>

    <dependencies>
        <module name="sun.jdk"/>
        <module name="javax.api"/>
        <module name="javax.servlet.api"/>
        <module name="javax.servlet.jsp.api"/>
        <module name="org.jboss.logging"/>
        <module name="org.jboss.modules"/>
    </dependencies>

</module>

但是，我不明白，模块的资源根路径中已经添加了jsp-api-2.1.jar，为什么还要为javax.servlet.jsp.api添加依赖。

JBoss 7: ClassCastException: MyCustomTag 无法转换为 javax.servlet.jsp.tagext.Tag

JBoss 7: ClassCastException: MyCustomTag cannot be cast to javax.servlet.jsp.tagext.Tag

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