我是 Struts 2 框架的新手。我编写了一个程序来理解 modelDriven 拦截器。但我无法执行它。以下是文件列表,最后有一个输出(错误)。
index.jsp:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib uri="/struts-tags" prefix="s"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%-- <jsp:useBean id="ent" class="pack.Entity" scope="session" /> --%>
<s:form method="get" action="go">
<s:textfield name="t1" label="Name"></s:textfield>
<s:password name="p1" label="Password"></s:password>
<s:submit value="accept"></s:submit>
</s:form>
</body>
</html>
Entity.java:
package actions_pack;
public class Entity {
private String t1;
private String p1;
public String getP1() {
return p1;
}
public void setP1(String p1) {
this.p1 = p1;
}
public Entity() {
super();
// TODO Auto-generated constructor stub
}
public String getT1() {
return t1;
}
public void setT1(String t1) {
this.t1 = t1;
}
}
GoAction.java:
package actions_pack;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpSession;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;
import com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor;
import com.opensymphony.xwork2.util.ValueStack;
public class GoAction implements ModelDriven<Entity> {
private Entity en;
public Entity getEn() {
return en;
}
public void setEn(Entity en) {
this.en = en;
}
public String execute(){
System.out.println("inside action");
if(en.getT1().equalsIgnoreCase("nitin")){
return "success";
}
else{
return "failure";
}
}
@Override
public Entity getModel() {
System.out.println("inside model driven....");
en=new Entity();
return en;
}
}
struts.xml:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
"http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>
<package name="dd">
<result-types>
<result-type name="dispatcher"
class="org.apache.struts2.dispatcher.ServletDispatcherResult"
default="true" />
</result-types>
<interceptors>
<interceptor name="modelDriven" class="com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor"/>
<interceptor-stack name="myStack">
<interceptor-ref name="modelDriven"></interceptor-ref>
</interceptor-stack>
</interceptors>
<action name="go" class="actions_pack.GoAction">
<interceptor-ref name="myStack"></interceptor-ref>
<result name="success" type="dispatcher" >/one/welcome.jsp</result>
<result name="failure" type="dispatcher">/one/error.jsp</result>
</action>
</package>
</struts>
welcome.jsp:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib uri="/struts-tags" prefix="s" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
Welcome, <s:property value="t1"/>
</body>
</html>
网页输出(500错误):
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
actions_pack.GoAction.execute(GoAction.java:24)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:450)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:289)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:252)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:563)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.34 logs.
Apache Tomcat/7.0.34
在 struts.xml
文件中,我不想使用/扩展 struts-default
包。尽管如此,当我在 struts.xml
中包含 params
拦截器条目以及 modelDriven
拦截器时,问题就解决了。这背后的原因是什么。有人可以指导我吗?
最佳答案
操作类中有一个属性需要在操作执行之前进行初始化。您可以通过多种方式做到这一点。
您选择的方式依赖于modelDriven
interceptor它在执行您的操作之前运行。它调用 getModel()
将其推送到 valueStack
的 top
上。因此,您的实体属性正在初始化。如果删除此拦截器,执行操作时您将收到 NullPointerException
。
如果您的Entity
是一个简单的POJO,您可以自己实例化,那么只需内联而不是在getModel()
中进行即可。
private Entity en = new Entity();
@Override
public Entity getModel() {
System.out.println("inside model driven....");
return en;
}
下一部分是关于params
interceptor 。如果您使用过 modelDriven
interceptor,它会使用 OGNL 填充作为模型的 top
对象。先前params
interceptor .
将它与您的操作一起使用可以初始化您在 execute()
中引用的一些属性。
例如,应初始化t1
。
关于java - 无法使用 ModelDriven 拦截器执行 Struts 2 程序,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24990948/