如何用焊接法方便地注入管柱常数?

我现在想要那笔赏金。弄清楚这一点让我对焊接的内部有了不少了解,这里有一个最有趣的教训:@Named是一个限定符,如果你想与之匹配,就必须这样对待它。

我确实有一个警告:如果你的应用程序中缺少任何值,它将在部署或加载时失败。这对您可能是可取的,但它确实意味着“默认”值是不可能的。

注入点的指定与上述完全相同,下面是使其工作所需的扩展代码:

@ApplicationScoped
public class PerformSetup implements Extension {

    Map<String, String> configMap;

    public PerformSetup() {
        configMap = new HashMap<String, String>();
        // This is a dummy initialization, do something constructive here
        configMap.put("string.value", "This is a test value");
    }

    // Add the ConfigMap values to the global bean scope
    void afterBeanDiscovery(@Observes AfterBeanDiscovery abd, BeanManager bm) {
        // Loop through each entry registering the strings.
        for (Entry<String, String> configEntry : configMap.entrySet()) {
            final String configKey = configEntry.getKey();
            final String configValue = configEntry.getValue();

            AnnotatedType<String> at = bm.createAnnotatedType(String.class);
            final InjectionTarget<String> it = bm.createInjectionTarget(at);

            /**
             * All of this is necessary so WELD knows where to find the string,
             * what it's named, and what scope (singleton) it is.
             */ 
            Bean<String> si = new Bean<String>() {

                public Set<Type> getTypes() {
                    Set<Type> types = new HashSet<Type>();
                    types.add(String.class);
                    types.add(Object.class);
                    return types;
                }

                public Set<Annotation> getQualifiers() {
                    Set<Annotation> qualifiers = new HashSet<Annotation>();
                    qualifiers.add(new NamedAnnotationImpl(configKey));
                    return qualifiers;

                }

                public Class<? extends Annotation> getScope() {
                    return Singleton.class;
                }

                public String getName() {
                    return configKey;
                }

                public Set<Class<? extends Annotation>> getStereotypes() {
                    return Collections.EMPTY_SET;
                }

                public Class<?> getBeanClass() {
                    return String.class;
                }

                public boolean isAlternative() {
                    return false;
                }

                public boolean isNullable() {
                    return false;
                }

                public Set<InjectionPoint> getInjectionPoints() {
                    return it.getInjectionPoints();
                }

                @Override
                public String create(CreationalContext<String> ctx) {
                    return configValue;

                }

                @Override
                public void destroy(String instance,
                        CreationalContext<String> ctx) {
                    // Strings can't be destroyed, so don't do anything
                }
            };
            abd.addBean(si);
        }
    }

    /**
     * This is just so we can create a @Named annotation at runtime.
     */
    class NamedAnnotationImpl extends AnnotationLiteral<Named> implements Named {
        final String nameValue;

        NamedAnnotationImpl(String nameValue) {
            this.nameValue = nameValue;
        }

        public String value() {
            return nameValue;
        }

    }
}

@ApplicationScoped
public class App {

    @Inject
    @Parameters
    List<String> parameters;

    @Inject
    @Named("string.value")
    String stringValue;

    public void printHello(@Observes ContainerInitialized event) {
        System.out.println("String Value is " + stringValue);
    }

}

最后,不要忘记/META-INF/services/javax.enterprise.inject.spi.Extension,将weldtest替换为您使用的类路径:

weldtest.PerformSetup

这应该能让这一切顺利。如果你遇到任何困难,请告诉我,我会把我的测试项目发给你。

对赏金不太感兴趣,但如果还摆在桌上的话,我会接受的。这与我在$DAYJOB上使用的一些代码非常相似,所以这不是理论,而是我在生产代码中使用的代码,但是为了保护罪犯而进行了修改。我还没有尝试编译修改过的代码,所以请注意,我可能在更改名称等方面犯了一些错误,但是这里涉及的原则都经过了测试并有效。

首先,您需要一个值持有者限定符。使用@Nonbinding可防止WELD只与具有相同值的限定符匹配,因为我们希望此特定限定符的所有值都与单个注入点匹配。通过将限定符和值保持在同一个注释中,您不能意外地“忘记”其中一个。(接吻原则)

@Qualifier
@Retention(RUNTIME)
@Target({METHOD, FIELD, PARAMETER, TYPE})
public @interface ConfigValue {
    // Excludes this value from being considered for injection point matching
    @Nonbinding 
    // Avoid specifying a default value, since it can encourage programmer error.
    // We WANT a value every time.
    String value();
}

接下来,需要一个知道如何获取地图的生产者方法。您可能应该有一个包含producer方法的命名bean,这样您就可以使用getter/setters显式地初始化该值,或者让bean为您初始化它。

@Named
public class ConfigProducer {
    //@Inject // Initialize this parameter somehow
    Map<String,String> configurationMap;

    @PostConstructor
    public void doInit() {
         // TODO: Get the configuration map here if it needs explicit initialization
    }

    // In general, I would discourage using this method, since it can be difficult to control exactly the order in which beans initialize at runtime.
    public void setConfigurationMap(Map<String,String> configurationMap) {
        this.configurationMap = configurationMap;
    }

    @Produces
    @ConfigValue("")
    @Dependent
    public String configValueProducer(InjectionPoint ip) {
        // We know this annotation WILL be present as WELD won't call us otherwise, so no null checking is required.
        ConfigValue configValue = ip.getAnnotated().getAnnotation(ConfigValue.class);
        // This could potentially return a null, so the function is annotated @Dependent to avoid a WELD error.
        return configurationMap.get(configValue.value());
    }
}

用法很简单:

@Inject
@ConfigValue("some.map.key.here")
String someConfigValue;

可能可以将其实现为一个@Dependent Producer方法,该方法本身会注入一个@InjectionPoint,这将允许您对要注入的字段进行反思——这将允许您查看字段上的一个自定义注释(而不是限定符)成员,以找出要返回的值

@Inject @ConfigMapQualifier @Val("user.name") String user;

...

@Produces @ConfigMapQualifier configProducr(...) { 
...
@Inject InjectionPoint ip;

// use e.g. ip/getJavaMember() then reflection to figure out the @Val value membr.

将实现自定义焊接 InjectionServices 不是这里的选择吗?

@Resource(name = "server.username", type = java.lang.String.class)
private String injectTo;

Javadoc公司: http://download.oracle.com/javase/6/docs/api/javax/annotation/Resource.html