构造函数注入在Servlet + WELD + Tomcat中不起作用

Question

我对CDI中的构造方法注入有疑问。现场或属性注入效果很好。构造函数注入的字段注入实例也可以正常工作。唯一的方法不起作用-Servlet类中的构造函数注入。

配置：WEB-INF中的空bean.xml，在context.xml中定义的BeanManager。

环境：Tomcat 9.0.24，CDI，WELD实现。

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>

Answer 1

您已经尝试降级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>