java.lang.IllegalAccessException：无法在 java.lang.Class 的类上调用 newInstance()答案

【问题标题】：java.lang.IllegalAccessException: Can not call newInstance() on the Class for java.lang.Classjava.lang.IllegalAccessException：无法在 java.lang.Class 的类上调用 newInstance()
【发布时间】：2014-06-12 18:00:24
【问题描述】：

在我的 spring 项目中，我实现了一个通用控制器作为我所有控制器的基础（我项目中的每个实体都有一个特定的控制器）。现在，当我尝试访问控制器映射的视图时，我遇到了这个错误：

java.lang.IllegalAccessException: Can not call newInstance() on the Class for java.lang.Class
    at java.lang.Class.newInstance(Class.java:339)
    at com.config.generic.controller.controller.createCommandObject(controller.java:84)
    at com.config.generic.controller.controller$$FastClassBySpringCGLIB$$56ef52f8.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:640)
    at com.usuario.controller.UsuarioController$$EnhancerBySpringCGLIB$$2c4051b5_2.createCommandObject(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:215)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
    at org.springframework.web.method.annotation.ModelFactory.invokeModelAttributeMethods(ModelFactory.java:123)
    at org.springframework.web.method.annotation.ModelFactory.initModel(ModelFactory.java:97)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:722)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:686)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:154)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:199)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:110)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:57)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:50)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:343)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:260)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

我的方法有这个共同的结构：

@RequestMapping(value="cadastra")
@PreAuthorize("hasPermission(#user, 'cadastra_#this.class.name')")
public ModelAndView cadastra() throws InstantiationException, IllegalAccessException {
    return new ModelAndView("privado/"+this.entity.getClass().getName()+"/cadastra", "command", this.entity.getClass().newInstance());
}

派生控制器具有以下结构：

@Controller
@RequestMapping(value="usuario")
public class UsuarioController extends controller<Usuario> {

    public UsuarioController() {
        super(Usuario.class);
    }

}

这个方法映射的jsp是这样的：

/WEB-INF/jsp/privado/Usuario/cadastra.jsp

<jsp:include page="../../common/cadastra.jsp">
    <c:url value="/Usuario/cadastra" var="cadastra"/>
    <jsp:param name="action" value="${cadastra}"/>
    <jsp:param name="elements" value="{params:[login,senha,pnome,unome,email]}"/>
</jsp:include>

/WEB-INF/jsp/common/cadastra.jsp

<%@ include file="../include/header.jsp" %>

<form:form class="form" role="form" action="${action}" method="post">

    <table>
        <c:forEach var="item" items="${elements}">
        <tr>
            <td><form:label path="${item}">${item}</form:label></td>
            <td><form:input type="" path="${item}" /></td> 
        </tr>
        </c:forEach>
        <tr>
            <td colspan="2">
                <button type="submit" class="btn btn-lg btn-primary">Cadastrar</button>
            </td>
        </tr>
    </table>

</form:form>

<%@ include file="../include/result.jsp" %>

<%@ include file="../include/footer.jsp" %>

我的通用控制器的完整代码如下：

https://github.com/klebermo/blog.cms/blob/master/src/main/java/com/config/generic/controller/controller.java

任何人都可以看到这个实现有什么问题？

【问题讨论】：

标签： java spring spring-mvc generics

【解决方案1】：

您的基类具有误导性。你有

@SuppressWarnings("unchecked")
public controller(Class<?> classe) {
    this.entity = (E) classe;
}

您称它为entity，但您在其中存储的是实体的类型，它是一个Class 对象。

改变

private final E entity;

到

private final Class<E> entityClass;

和

@SuppressWarnings("unchecked")
public controller(Class<?> classe) {
    this.entity = (E) classe;
}

到

public controller(Class<E> classe) {
    this.entityClass = classe;
}

和

return new ModelAndView("privado/"+this.entity.getClass().getName()+"/cadastra", "command", this.entity.getClass().newInstance());

到

return new ModelAndView("privado/"+this.entityClass.getName()+"/cadastra", "command", this.entityClass.newInstance());

同时更改需要该字段的任何其他内容。

【讨论】：