@Inject字段始终为null [英] @Inject field is always null

问题描述

我尝试@Inject一个字段（它是一个jar模块，空的beans.xml存在于META-INF下），如下所示：

I try to @Inject a field (its a jar module, empty beans.xml is existing under META-INF) like this:

IDataProvider Interface

IDataProvider Interface

public interface IDataProvider {
  void test();
}

DataProvider实现
import javax.enterprise.context.ApplicationScoped;

DataProvider implementation import javax.enterprise.context.ApplicationScoped;

@ApplicationScoped
public class DataProvider implements IDataProvider {
  private int i;

  public DataProvider() {
    i = 42;
  }

  @Override
  public void test() {

  }
}

我尝试注入DataProvider的类

And the class where i try to inject the DataProvider

import javax.enterprise.context.ApplicationScoped;
import javax.inject.Inject;

@ApplicationScoped
public class DataController {

  @Inject
  private IDataProvider dataProvider;

  private int k;

  public DataController() {
     k = 42;
  }
}

如果我在Wildfly上运行它，注入的dataProvider总是null（DataController构造函数中的断点）。

If i run this on Wildfly the injected dataProvider is always null (Breakpoint at DataController constructor).

在每个教程上都是这样做的，所以我认为这应该有效。唯一的区别是两个类都应该是@ApplicationScoped

On every tutorial it's done like this, so i thought this should work. Only difference is that both classes should be @ApplicationScoped

我正在使用Wildfly 8.2Final，Gradle，IntelliJ。
我的gradle.build看起来像这样：

I am using Wildfly 8.2Final, Gradle, IntelliJ. My gradle.build looks like this:

apply plugin: 'java'

repositories {
  mavenCentral()
  jcenter()
}

dependencies {
  compile group:'javax', name:'javaee-web-api', version:'7.+'
  compile group:'org.jboss.ejb3', name:'jboss-ejb3-ext-api', version:'2.+'
}

sourceSets {
  main {
      java {
          srcDir 'src/api/java'
          srcDir 'src/main/java'
      }
  }

  test {
      java {
          srcDir 'src/test/java'
      }
  }
}

jar {
  from ('./src') {
      include 'META-INF/beans.xml'
  }
}

有没有人知道为什么这不起作用？我没有从Wildfly获得任何错误或异常。

Does anyone have an idea why this is not working? i dont get any error or exception from Wildfly.

推荐答案

在构建 DataController期间， dataProvider 为空是正常的。在此之后进行注入。

During the construction of the DataController, it's normal the dataProvider is null. Injection happens after that.

您应该添加 @PostConstruct 方法来检查字段的无效性：

You should add a @PostConstruct method to check for nullity of the field:

@PostConstruct
void init() {
    // dataProvider should not be null here.
}

另外，Weld的错误报告工作做得非常好。因此，如果注入失败，您应该有一个明确而详细的错误消息，而不仅仅是一个空字段。

Aditionally, error reporting on Weld is pretty well done. So you should have an explicit and detailed error message if the injection fails, and not only a null field.

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