泽西岛@Context范围

Question

我很难理解泽西岛的注入机制。JAX-RS规范(http://jsr311.java.net/nonav/releases/1.1/spec/spec3.html#x3-520005）指出，在应用程序子类、根资源类和提供程序中可以通过@Context进行注入。

我现在有一个在启动时实例化的类，并且有一个在每次请求时调用的方法。在方法内部，我需要访问当前的UriInfo对象。问题是，这个方法不是从我的代码中调用的。所以我不能把UriInfo直接传递给方法。

我实际上想做这样的事情：

public class MyClass implements ThirdPartyInterface {

    // not possible because class is no Application subclass, root resource class or provider
    @Context
    private UriInfo uriInfo;

    public void methodCallebByThirdPartyCode() {
        Uri requestUri = uriInfo.getRequestUri();

        // do something
    }
}

我试过这个。显然没有成功:

public class MyClass implements ThirdPartyInterface {

    private UriInfo uriInfo;

    public MyClass(UriInfo uriInfo) {
        this.uriInfo = uriInfo;
    }

    public void methodCallebByThirdPartyCode() {
        Uri requestUri = uriInfo.getRequestUri();

        // do something
    }
}

@Provider
@Produces(MediaType.WILDCARD)
public class MyBodyWriter implements MessageBodyWriter<MyView> {

    @Context
    private UriInfo uriInfo;

    private MyClass myClass;

    private ThirdPartyClass thirdPartyClass;

    public MyBodyWriter() {
        // uriInfo is null at this time :(
        myClass = new MyClass(uriInfo);

        thirdPartyClass = new ThirdPartyClass();
        thirdPartyClass.register(myClass);
    }

    public void writeTo(final MyView view, final Class<?> type, /* and so on */) throws IOException, WebApplicationException {
        // execute() calls MyClass#methodCallebByThirdPartyCode()
        thirdPartyClass.execute();
    }
}

我能想到的唯一解决办法是这个。我不认为它很干净：

java prettyprint-override">public class MyClass implements ThirdPartyInterface {

    private UriInfo uriInfo;

    public void setUriInfo(final UriInfo uriInfo) {
        this.uriInfo = uriInfo;
    }

    public void methodCallebByThirdPartyCode() {
        Uri requestUri = uriInfo.getRequestUri();

        // do something
    }
}

@Provider
@Produces(MediaType.WILDCARD)
public class MyBodyWriter implements MessageBodyWriter<MyView> {

    @Context
    private UriInfo uriInfo;

    private MyClass myClass;

    private ThirdPartyClass thirdPartyClass;

    public MyBodyWriter() {
        myClass = new MyClass();

        thirdPartyClass = new ThirdPartyClass();
        thirdPartyClass.register(myClass);
    }

    public void writeTo(final MyView view, final Class<?> type, /* and so on */) throws IOException, WebApplicationException {
        myClass.setUriInfo(uriInfo);

        // execute() calls MyClass#methodCallebByThirdPartyCode()
        thirdPartyClass.execute();

        myClass.setUriInfo(null);
    }
}

我希望有更好的解决方案，但也许我完全走错了方向。

谢谢

Answer 1

回答晚了，但是一个好问题...所以我们走吧:

您可以使用org.glassfish.hk2.api.Factory和javax.inject.Provider进行注射。我不知道从哪个版本开始可用，所以也许你必须升级你的jersery版本。对于以下示例，我使用了jersey 2.12。

首先，您必须为 MyClass 实现并注册/绑定工厂：

我的类工厂：

import javax.inject.Inject;
import javax.ws.rs.core.UriInfo;
import org.glassfish.hk2.api.Factory;
// ...

public class MyClassFactory implements Factory<MyClass> {

    private final UriInfo uriInfo;

    // we will bind MyClassFactory per lookup later, so 
    // the constructor will be called everytime we need the factory
    // meaning, uriInfo is also per lookup

    @Inject
    public MyClassFactory(final UriInfo uriInfo) {
        this.uriInfo = uriInfo;
    }

    @Override
    public MyClass provide() {
        return new MyClass(uriInfo) 
    }

    @Override
    public void dispose(UriInfo uriInfo) {
        // ignore 
    }

}

通过资源配置注册:

import org.glassfish.hk2.api.PerLookup;
import org.glassfish.hk2.utilities.binding.AbstractBinder;
import org.glassfish.jersey.server.ResourceConfig;
// ...

public class MyResourceConfig extends ResourceConfig {

    public MyResourceConfig() {
        register(new AbstractBinder() {
            @Override
            protected void configure() {
                bindFactory(MyClassFactory.class).to(MyClass.class).in(PerLookup.class);
                // ... bind additional factories here
            }
        });
        // ...
    }

}

现在，您可以为每个查找注入MyClass到提供者，资源等，
但是请注意：Afaig有两种方法，只有一种方法可以最终用于提供者...

import javax.inject.Inject;
import javax.ws.rs.Produces;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;
// ...

@Provider
@Produces("application/foo-bar")
public class MyBodyWriter implements MessageBodyWriter<MyView> {

    // first approache - don't do it!
    // will only injected once, cause MyBodyWriter is only instantiated once
    @Inject
    private MyClass myClass;

    // second approache - works fine!
    private final javax.inject.Provider<MyClass> provider;

    // MyBodyWriter instantiate once
    // get an inject provider here
    @Inject
    public MyBodyWriter(javax.inject.Provider<MyClass> myClassProvider) {
        this.provider = myClassProvider;
    }

    @Override
    public boolean isWriteable(Class<?> t, Type g, Annotation[] a, MediaType m) {
        return t == MyView.class;
    }

    @Override
    public long getSize(MyView t, Class<?> c, Type g, Annotation[] a, MediaType m) {
        // deprecated by JAX-RS 2.0 and ignored by Jersey runtime
        return 0;
    }

    @Override
    public void writeTo(MyView v, Class<?> c, Type t, Annotation[] a, MediaType m, MultivaluedMap<String, Object> s, OutputStream o) throws IOException, WebApplicationException {

        // attention: its not per lookup !!!
        MyClass myClassDirectInjected = myClass;
        System.out.println(myClassDirectInjected); // same instance everytime

        // but this is ;)
        MyClass myClassFromProvider = provider.get();
        System.out.println(myClassFromProvider); // it's a new instance everytime

        // ...
    }

}

希望这能有所帮助。