将ThreadLocal与Filter、HttpSession和Session属性一起使用时的不一致性

Question

我使用的是一个存储字符串的ThreadLocal对象。我将String值设置为过滤器中的ThreadLocal对象，该对象将截取符合特定条件的所有请求。另外，我将ThreadLocal的字符串值设置为HttpSession作为属性。

那么，有什么方法可以改变实现，使多个会话不使用同一个线程呢？

编辑：添加示例代码

public class ContextFilter implements Filter {

    //No significant variables other than constants

    public void doFilter(ServletRequest request, ServletResponse response,
                FilterChain chain) throws IOException, ServletException {

            // Set the Session Timeout Object
            SessionTimeoutObject obj = (SessionTimeoutObject) httpRequest
                    .getSession().getAttribute(KEY);
            if (obj == null) {
                httpRequest.getSession().setAttribute(KEY,
                        new SessionTimeoutObject());
            }

            if( some conditions ) {
                chain.doFilter(request, response);
            } else {
                //Defaulting identifier
                String identifier = "init";

                if (ContextHolder.getId() != null
                        && !ContextHolder.getId().equals("")) {
                    identifier = ContextHolder.getId());
                }

                //Do some thing 

                //Compare the identifier with the value in session and use if it exists
                String existingId = (String) httpRequest.getSession()
                        .getAttribute(ID_KEY);
                if (existingId != null
                        && !existingId.trim().equals("")) {
                    identifier = existingId;
                }

                //Setting id to context only happens here
                ContextHolder.setId(identifier);
                //Validate the identifier

                //Get Business Obj method using identifier
                BusinessObj bo = getBusObj(identifier);

                //everything above is successful so set in session
                httpRequest.getSession().setAttribute("identifier", identifier);
                httpRequest.getSession().setAttribute("BusinessObj",
                    bo);

                //no exceptions yet then good to go
                chain.doFilter(request, response);
            }

    }


}

public class SessionTimeoutObject implements Serializable, HttpSessionBindingListener {

    private String backup;

    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        //Mainly for debuggin what happens to the session
        backup = (String) event.getSession().getAttribute("identifier");
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        //Mainly for debuggin what happens to the session
        if (ContextHolder.getId() != null) {
            backup = ContextHolder.getId();
        } 
    }

}

class ContextHolder {

    private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();

    public ContextHolder() {
    }

    public static void setId(String identifier) {
        if (null == identifier) {
            //throw some exception
        }
        contextHolder.set(identifier);
    }

    public static String getId() {
        return (String) contextHolder.get();
    }

    public static void clearId() {
        contextHolder.remove();
    }

    public static void setDefaultId() {
        ContextHolder.clearId();
        contextHolder.set('init');
    }
}

Answer 1

您应该将代码包装在try/finally块中，在finally块中执行contextholder.clearid（）以清除上下文持有者。这一点很重要，因为请求处理线程是重用的，这意味着ContextHolders线程本地保留与以前相同的id。-M.Deinum

做到以上几点就解决了问题。