依赖注入 – 泽西@Context范围

发布时间：2020-12-13 20:44:19 所属栏目：百科来源：网络整理

导读：我很难理解泽西的注射机制. JAX-RS规范( http://jsr311.java.net/nonav/releases/1.1/spec/spec3.html#x3-520005)规定,可以在Application子类,根资源类和提供程序中通过@Context进行注入. 我现在有一个在启动时实例化的类,并且有一个在每个请求上调用的方法.

我很难理解泽西的注射机制. JAX-RS规范( http://jsr311.java.net/nonav/releases/1.1/spec/spec3.html#x3-520005)规定,可以在Application子类,根资源类和提供程序中通过@Context进行注入.

我现在有一个在启动时实例化的类,并且有一个在每个请求上调用的方法.在方法内部,我需要访问当前的UriInfo对象.问题是,我的代码没有调用此方法.所以我无法直接将UriInfo传递给该方法.

我其实想做这样的事情：

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方法就是这个.我不认为它很干净：

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,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路.

谢谢！

迟到的回答,但是一个很好的问题…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可用,所以也许你必须升级你的jersery版本.对于以下样品,我使用了汗布2.12.

首先,您必须为MyClass实现并注册/绑定Factory：

MyClassFactory：

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ResourceConfig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,您可以将每个查询的MyClass注入提供者,资源等.
但注意：Afaig有两种方法,只有一种方法最终会被视为提供者…

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,MediaType m) {
        // deprecated by JAX-RS 2.0 and ignored by Jersey runtime
        return 0;
    }

    @Override
    public void writeTo(MyView v,Type t,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

        // ...
    }

}

希望这在某种程度上有所帮助.

（编辑：李大同）

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