execAndWait 拦截器不适用于验证答案

【问题标题】：execAndWait interceptor not working with validationexecAndWait 拦截器不适用于验证
【发布时间】：2015-04-26 11:22:15
【问题描述】：

当使用execAndWait 拦截器和validate() 方法时，我得到NullPointerException。在index.jsp 中，我有一个textfield 用于firstName。当我提交时，它首先在 Action 类中使用 validate 方法 validate 那个字符串。然后转到execute 方法。在输出中，我得到NullPointerException 的firstName 字段在validate 方法中找不到。我在某处了解到，execAndWait 在单独的线程中运行，这就是出现此问题的原因。我想知道如何解决这个问题。下面的文件明智代码：

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>
    <s:actionerror />
    <s:actionmessage />
    <s:form action="go" method="post">
        <s:textfield name="fname" label="First-Name" />
        <s:submit value="enter"></s:submit>
    </s:form>
</body>
</html>

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="abc" extends="struts-default">

        <interceptors>
            <interceptor-stack name="myStack">
                <interceptor-ref name="defaultStack"></interceptor-ref>
                <interceptor-ref name="execAndWait"></interceptor-ref>
            </interceptor-stack>
        </interceptors>

        <action name="go" class="pack.GoAction">
            <interceptor-ref name="myStack" />
            <result name="success">/success.jsp</result>
            <result name="failure">/failure.jsp</result>
            <result name="input">/index.jsp</result>
            <result name="wait">/wait.jsp</result>
        </action>
    </package>
</struts>

GoAction.java:

package pack;
import java.sql.*;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;
public class GoAction extends ActionSupport implements ModelDriven<User> {
    private static final long serialVersionUID = 1L;
    private User user;
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    @Override
    public User getModel() {
        System.out.println("****inside getModel()****");
        user=new User();
        return user;
    }

    public void validate(){
        System.out.println("****inside validate****");
        if(user.getFname().length()<4){
            this.addFieldError("fname", "first name can not be less than 5");
            System.out.println("console: first name can not be less than 5 "+user.getFname());
        }
        if(user.getFname().length()==0){
            this.addFieldError("fname", "first name found empty");
        }
    }

    public String execute(){
        System.out.println("****inside execute****");
        String returnValue="";
        int i=0;
        Connection con=null;
        ResultSet rs=null;
        PreparedStatement ps=null;
        if(user.getFname().equals("zebra")){
            System.out.println("First-Name : zebra : not allowed.");
            this.addActionMessage("First-Name : zebra : not allowed");
            return "failure";
        }
        try{
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "hibernate", "hibernate");
            ps=con.prepareStatement("insert into table1 values(?)");
            ps.setString(1, user.getFname());
            i=ps.executeUpdate();
            if(i!=0){
                returnValue="success";
                this.addActionMessage("data successfully inserted");
                System.out.println("ok");
            }
            else{
                returnValue="failure";
                System.out.println("not ok");
            }
        }catch(Exception ex){
            System.out.println("E x c e p t i o n    o c c u r r e d  !!!!");
            ex.printStackTrace();
        }
        return returnValue;
    }
}

wait.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>Wait...</title>
<meta http-equiv="refresh" content="1;">
</head>
<body>
    <img src="images/animation_processing.gif" />
</body>
</html>

success.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>
    Success !!
    <br>
    <s:actionmessage />
</body>
</html>

输出屏幕（逐步）

然而值被插入到数据库中：

控制台输出

****inside getModel()****
****inside validate****
****inside execute****
Apr 26, 2015 4:30:48 PM org.apache.struts2.util.TokenHelper warn
WARNING: Could not find token mapped to token name token
ok
****inside getModel()****
****inside validate****
Apr 26, 2015 4:30:50 PM org.apache.struts2.dispatcher.Dispatcher error
SEVERE: Exception occurred during processing request: null
java.lang.NullPointerException
    at pack.GoAction.validate(GoAction.java:35)
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doBeforeInvocation(ValidationInterceptor.java:251)
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:263)
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:239)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:239)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:252)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:161)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:563)
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
    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:472)
    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:936)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
    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(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

经过一番浏览，我知道execAndWait 在单独的线程中运行，无法获取user.getFname() 的值。谁能帮我解决这个问题。

【问题讨论】：

标签： java validation jsp struts2

【解决方案1】：

更改验证方法的逻辑

public void validate(){
    System.out.println("****inside validate****");
    if(user.getFname() == null || user.getFname().length()==0){
        this.addFieldError("fname", "first name found empty");
    } else
    if(user.getFname().length()<4){
        this.addFieldError("fname", "first name can not be less than 5");
        System.out.println("console: first name can not be less than 5 "+user.getFname());
    }
}

【讨论】：

它的意思是“发现名字为空”。即使它将值插入到 db.另外，如果我从struts.xml 文件中删除execAndWait 拦截器条目，则验证方法的旧代码没有问题。
是在将值插入到数据库之前还是之后？
首先很抱歉反应太晚了。这是我得到的控制台输出： ****在 getModel()**** **** 在 validate**** **** 在执行**** 2015 年 4 月 26 日 10:33： 00 PM org.apache.struts2.util.TokenHelper 警告警告：找不到映射到令牌名称令牌的令牌 ok ****inside getModel()**** ****inside validate****
你能告诉我...为什么又进入getModel()和validate()方法？如果我从 struts.xml 中删除 execAndWait 拦截器条目，则输出显示：****inside getModel()**** ****inside validate**** ****inside execute****
你应该阅读execAndWait拦截器是如何工作的，它会在一段时间后返回一个wait结果来一次又一次地调用你的动作，直到动作被执行。如果它没有参数，它们将不会被设置为动作并且验证总是失败。如果您从堆栈中删除validation 拦截器，或者干脆不要将execAndWait 拦截器用于发布请求。

【解决方案2】：

解决方案在于execAndWait 拦截器的工作方式以及struts2 框架调用方法的方式（getModel()，然后是validate()，然后是execute）。另请注意，execAndWait 在不同的线程中运行。您不能使用 ActionContext，因为它是 ThreadLocal。这意味着如果您需要访问例如会话数据，您需要实现 SessionAware 而不是调用 ActionContext.getSession()。

----execAndWait 是如何工作的-----

正如@Roman C 和 API Docs 所说的

execAndWait 在超时后返回等待结果，以一次又一次地调用您的操作，直到执行该操作。如果它没有参数，它们将不会被设置为动作并且验证总是失败。

上面的程序抛出NullPointerException，因为execAndWait拦截器在每1秒间隔后重复调用getModel()（以及validate()）（参见wait.jsp <meta http-equiv="refresh" content="1;"/>）。

所以当它再次调用getModel() 时，它会设置原始new User();object，即没有任何参数fname。因此，在getModel() 之后，它再次进入validate()。而这一次它发现fname 是null。因此，要解决上述问题，只需将 GoAction 类替换为以下代码：

开始行动

package pack;
import java.sql.*;
import java.util.Map;
import org.apache.struts2.dispatcher.SessionMap;
import org.apache.struts2.interceptor.SessionAware;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;
public class GoAction extends ActionSupport implements ModelDriven<User>,SessionAware {
    private SessionMap<String, Object> sm;
    private static final long serialVersionUID = 1L;
    private User user;
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    @Override
    public User getModel() {
        System.out.println("****inside getModel()****");
        User u=(User) sm.get("user");
        if(u==null){
            user=new User();
        }
        else{
            user=u;
        }
        return user;
    }

    public void validate(){
        sm.put("user", user);
        User u=(User) sm.get("user");
        System.out.println("^^^"+u.getFname());
        System.out.println("****inside validate****");
        if(u.getFname().length()<4){
            this.addFieldError("fname", "first name can not be less than 5");
            System.out.println("console: first name can not be less than 5 "+user.getFname());
        }
    }

    public String execute() throws InterruptedException{
        System.out.println("****inside execute****");
        String returnValue="";
        int i=0;
        Connection con=null;
        ResultSet rs=null;
        PreparedStatement ps=null;
        if(user.getFname().equals("zebra")){
            System.out.println("First-Name : zebra : not allowed.");
            this.addActionMessage("First-Name : zebra : not allowed");
            return "failure";
        }
        try{
            Class.forName("oracle.jdbc.driver.OracleDriver");
            con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "hibernate", "hibernate");
            ps=con.prepareStatement("insert into table1 values(?)");
            ps.setString(1, user.getFname());
            i=ps.executeUpdate();
            if(i!=0){
                returnValue="success";
                this.addActionMessage("data successfully inserted");
                System.out.println("ok");
            }
            else{
                returnValue="failure";
                System.out.println("not ok");
            }
        }catch(Exception ex){
            System.out.println("E x c e p t i o n    o c c u r r e d  !!!!");
            ex.printStackTrace();
        }
        return returnValue;
    }
    @Override
    public void setSession(Map<String, Object> sm) {
        this.sm=(SessionMap<String, Object>) sm;
    }
}

在这段代码中，我在getModel() 方法中检查user 对象存储的会话映射。如果未找到：new User()。如果找到：返回它。

【讨论】：