构造函数注入在 Servlet + WELD + Tomcat 中不起作用

Question

我在 CDI 中遇到构造函数注入问题。 字段或属性注入工作正常。 字段注入实例的构造函数注入也可以正常工作。 唯一不工作的 - Servlet 类中的构造函数注入。

配置：空beans.WEB-INF中的xml，context中定义的BeanManager.xml。

环境：Tomcat 9.0.24，CDI，WELD 实施。

示例代码：

@WebServlet(urlPatterns = "/servlet/*")
public class SimpleServlet extends HttpServlet implements Serializable {

// @Inject
private TestService testService;

@Inject
public SimpleServlet(TestService testService) {
    this.testService = testService;
}

// Without this constructor (even protected) I have Exception java.lang.NoSuchMethodException: SimpleServlet.<init>()
public SimpleServlet() {
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // This prints null when using constructor injection
    // Prints instance hashcode when using field injection
    resp.getWriter().write(testService + "");
}

@PostConstruct
public void onPostConstruct() {
    System.out.println("This is invoked everytime");

    // Null when constructor injection
    System.out.println(testService);
}
}

POM.xml

<dependencies>
    <dependency>
        <groupId>javax</groupId>
        <artifactId>javaee-web-api</artifactId>
        <version>8.0</version>
        <scope>provided</scope>
    </dependency>

    <dependency>
        <groupId>javax.enterprise</groupId>
        <artifactId>cdi-api</artifactId>
        <version>2.0.SP1</version>
    </dependency>

    <dependency>
        <groupId>org.jboss.weld.servlet</groupId>
        <artifactId>weld-servlet-shaded</artifactId>
        <version>3.1.2.Final</version>
    </dependency>
</dependencies>

Servlet 内 ConstructorInjection 的 StackTrace：

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:151)
at org.jboss.weld.environment.tomcat.ForwardingInstanceManager.newInstance(ForwardingInstanceManager.java:26)
at org.jboss.weld.environment.tomcat.WeldForwardingInstanceManager.newInstance(WeldForwardingInstanceManager.java:71)

以及其他 class 内部的 ConstructorInjections：

at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.jboss.weld.injection.ConstructorInjectionPoint.newInstance(ConstructorInjectionPoint.java:119)
at org.jboss.weld.injection.ConstructorInjectionPoint.invokeAroundConstructCallbacks(ConstructorInjectionPoint.java:92)
at org.jboss.weld.injection.ConstructorInjectionPoint.newInstance(ConstructorInjectionPoint.java:78)

所以 Servlet 内部的 WELD 使用 ForwardingIntranceManager，但在其他类 ConstructorInjectionPoint 内部。 WELD里面的错误可能吗？

Answer 1

您是否已经尝试过降级 CDI 版本？ 尝试在 pom.xml 中更改这些依赖项。

<dependency>
  <groupId>javax.enterprise</groupId>
  <artifactId>cdi-api</artifactId>
  <version>1.2</version>
</dependency>

<dependency>
  <groupId>org.jboss.weld.servlet</groupId>
  <artifactId>weld-servlet</artifactId>
  <version>2.2.9.Final</version>
</dependency>