在ServerResource发送的表示形式上设置ETAG/LastModified [英] Setting ETAG/LastModified on Representation sent by ServerResource

问题描述

我知道我可以在Representation/RepresentationInfo上设置ETAG和LastModified属性.但是我有一个实现这样的简单资源:

I know I can set the ETAG and LastModified properties on Representation/Repre​sentationInfo. But I have a simple resource implemented like this :

public class AccountServerResource extends ServerResource implements AccountResource {

    private static Logger log = Logger.getLogger(Acc​ountServerResource.c​lass.getName());

    @Override
    public Account retrieve() {
        User user = getClientInfo().getUser();
        AccountDAO dao = new AccountDAO();
        Account ret = dao.getAccountByEmai​l(user.getEm​ail());
        log.info("retrieved " + ret);
        // getResponse().getEntity() == null at this point !!!
        // ---> cannot do this : getResponse().getEntity().setModificationDate(ret.getLastMod​ified());
        return ret;
    }   
}

此表示目前尚未附加到响应中.我何时/如何设置ETAG/LastModified标签?

The representation is not yet attached to the response at this time. When/how do I set the ETAG/LastModified tags ?

这里推荐的做法是什么?

What is the recommended practice here ?

---更新---

我没有运气就尝试过这种方法:

I tried this approach without luck :

@Override
public Account retrieve() {
        User user = getClientInfo().getUser();
    AccountDAO dao = new AccountDAO(user.getN​amespace());
        AccountDAO dao = new AccountDAO();
        Account ret = dao.getAccountByEmai​l(user.getEm​ail());
    log.info("retrieved " + ret);
    setOnSent(new StrongEtagCallback​<Account>(ret));​
    return ret;
}

StrongEtagCallback的实现如下:

And implementation of the StrongEtagCallback like this :

public class StrongEtagCallback<T extends DomainResource> implements Uniform {

    private static SimpleDateFormat df = new SimpleDateFormat("dd​MMyyyyHHmmssSSS");
    private DomainResource d;

    public StrongEtagCallback(T domainResource) {
        d = domainResource;
    }

    @Override
    public void handle(Request request, Response response) {
        String eTag = d.getClass().getSimpleName() + "-" + d.getId() + "-" + df.format(d.getLastModified());
        response.getEntity().setTag(new Tag(eTag, false));
    }
}

我所有的实体都在其中实现DomainResource，这要求它们具有ID和LastModified日期.

Where all my entities implement DomainResource which require them to have an ID and LastModified date.

但是它不起作用.我真的希望它能正常工作，这非常优雅！

尽管正在调用StrongEtagCallback，但ETAG在实体的服务器端设置了.我的Wireshark或我的GWT客户端都在响应中看到一个E-TAG标头.现在跳得更深.

The StrongEtagCallback is being called though, the ETAG set server-side on the entity. My Wireshark nor my GWT client sees a E-TAG header on the response of the response. Diving deeper now.

推荐答案

在我自己研究此问题时，我注意到

In researching this issue myself, I noticed a parallel thread started by koma on the Restlet discussion board, in which an alternative and preferable solution was provided by Tim Peierls, namely to override Resource.toRepresentation().

正如koma在那个线程中指出的那样，覆盖 ServerResource.handle()会导致条件匹配失败(我不确定为什么吗?)，所以这种方法是有问题的.

As koma pointed out in that thread, overriding ServerResource.handle() caused conditions matching to fail (I'm not sure why?), so that approach is problematic.

蒂姆·皮尔斯(Tim Peierls)提供的示例替代代码:

Example override code provided by Tim Peierls:

@Override public Representation toRepresentation(Object source, Variant target) {
    Representation rep = super.toRepresentation(source, target);
    if (source instanceof HasLastModified) {
        HasLastModified hlm = (HasLastModified) source;
        rep.setModificationDate(hlm.getLastModified());
    }
    if (source instanceof HasEtag) {
        HasEtag he = (HasEtag) source;
        rep.setTag(he.gettag());
    }
    return rep;
}

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