Question

我使用jsp和servlet创建了一个小型Web应用程序。我的ajax post方法每三秒调用一次java类。我想知道每3秒，java类变量isBootRunning，istest1Running，istest1Running被初始化为＆＃34; null＆＃34;或不。如果它将为每个请求初始化，如何防止这种初始化。

我的JSP：

setInterval(function(){
            TestReport(); 
        }, 3000); 
function TestReport(){
var tbname = $("#tbname").attr('class');
var userName = $("#userName").attr('class');
var name = tbname;
var url ="TestReport";
var params = {
        tbname: tbname,
        userName:userName
};
$.post('TestReport', {
    tbname: tbname,
    userName:userName,
}, function(responseText) {
    alert(responseText);
});
}

我的Servlet：

public class TestReport extends HttpServlet {
private static final long serialVersionUID = 1L;
String isBootRunning = null;
String istest1Running = null;
String istest2Running = null;
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        File f1 = new File("myfirstpath");//this directory is visible for 10 mins only 
        File f2 = new File("mythirdpath");//this directory is visible for 10 mins only
        File f3 = new File("mythirdpath");//this directory is visible for 10 mins only

        if (f1.exists() && f1.isDirectory()) {
            isBootRunning = "Running";
            istest1Running = "Scheduled";
            istest2Running = "Scheduled";
        } else if(f2.exists() && f2.isDirectory()){
            istest1Running = "Running";
            istest2Running = "Scheduled";
            if(isBootRunning=="Running"){
                //here my logic
            }
        } else if(f2.exists() && f2.isDirectory()){

            istest2Running = "Running";
            if(isBootRunning=="Running"){
                //here my logic
            }
            if(istest1Running=="Running"){
                //here my logic
            }
        }
    }
}

Answer 1

您遇到此问题，因为每次向servlet发出新的ajax请求时，都不会存储/保存先前请求的结果。
可以使用 HttpSession 解决此问题。您必须在会话对象中保存并获取字符串对象isBootRunning，istest1Running，istest2Running，如下所示：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try{
        HttpSession session =null;
        if(request.getSession().isNew()){
             session= request.getSession();//new session
        }else{
             session= request.getSession(false);//current session
        }
        if(null != session && null != session.getAttribute("isBootRunning") && null != session.getAttribute("istest1Running")  && null != session.getAttribute("istest2Running")){ 
            yourLogic(session);//compute your logic for not null values
        }
        else{
            session.setAttribute("isBootRunning", "");
            session.setAttribute("istest1Running", "");
            session.setAttribute("istest2Running", "");

            yourLogic(session);//compute your logic for null values
        }

    }catch(Exception e){
        e.printStackTrace();
    }
}

private void yourLogic(HttpSession session) {
    File f1 = new File("myfirstpath");//this directory is visible for 10 mins only 
    File f2 = new File("mythirdpath");//this directory is visible for 10 mins only
    File f3 = new File("mythirdpath");//this directory is visible for 10 mins only

    String isBootRunning = (String)session.getAttribute("isBootRunning");
    String istest1Running = (String)session.getAttribute("istest1Running");;
    String istest2Running = (String)session.getAttribute("istest2Running");;
    if (f1.exists() && f1.isDirectory()) {
        session.setAttribute("isBootRunning", "Running");
        session.setAttribute("istest1Running", "Scheduled");
        session.setAttribute("istest2Running", "Scheduled");
    } else if(f2.exists() && f2.isDirectory()){
        session.setAttribute("istest1Running", "Scheduled");
        session.setAttribute("istest2Running", "Scheduled");
        if(isBootRunning=="Running"){
            //here my logic
        }
    } else if(f2.exists() && f2.isDirectory()){
        session.setAttribute("istest2Running", "Scheduled");
        istest2Running = "Running";
        if(isBootRunning=="Running"){
            //here my logic
        }
        if(istest1Running=="Running"){
            //here my logic
        }
    }
}

这里，您的String对象存储在会话对象中。并且使用会话是非常安全的，因为会话管理是在您的Web容器中完成的，并且它永远不会破坏用户的完整性这将阻止对象的初始化以供以后的请求使用。

Answer 2

你必须写来获取变量：

    String isBootRunning = (String) getServletContext().getAttribute("isBootRunning");

您必须写入设置变量：

    getServletContext().setAttribute("isBootRunning", isBootRunning);

Answer 3

另一件事是当前的设计非常糟糕（可能的竞争条件）。应用程序/ Web容器是多线程的。由于您没有使用任何sychonronization，当另一个线程提供请求时，您可能看不到结果。

post方法调用一个java类初始化每个请求

3 个答案: