java jvax 注入(inject)失败并出现空点 NullPointerException

Question

我尝试在我的项目中使用依赖注入(inject)。我犯了一些错误，但我看不到我的失败。

我的项目设置:

Maven main project
|-- maven module "model"
  |-- org.inject.test.model
    |-- Address.java
    |-- User.java
  |-- org.inject.test.model.manger
    |-- UserManager.java
|-- maven module "core"
  |-- org.inject.test.core
    |-- MyMain.java
 |-- org.inject.test.core.managerImpl
   |-- UserManagerImpl.java

地址.类:

package org.inject.test.model;

public class Address {

    private String street;

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }
}

用户.类:

package org.inject.test.model;

import javax.inject.Inject;
import javax.inject.Named;

import org.inject.test.model.manager.UserManager;

@Named
public class User {

    private String name;
    private Address address;

    @Inject
    private UserManager usermanager;

    public User (String name) {
        this.name = name;
        address = null;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Address getAddress() {
        if (address == null) {
            address = usermanager.getAddress();
        }
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }
}

用户管理器界面:

package org.inject.test.model.manager;

import org.inject.test.model.Address;

public interface UserManager {

    public Address getAddress ();
}

用户管理器实现:

package org.inject.test.core.managerImpl;

import javax.inject.Named;

import org.inject.test.model.Address;
import org.inject.test.model.manager.UserManager;

@Named
public class UserManagerImpl implements UserManager {

    public Address getAddress() {
        // Do the DB stuff here (DB.getAddress...)
        Address address = new Address();
        address.setStreet("My test street");

        return address;
    }
}

我的主类:

package org.inject.test.core;

import javax.inject.Inject;

import org.inject.test.model.Address;
import org.inject.test.model.User;
import org.inject.test.model.manager.UserManager;
import org.jboss.weld.environment.se.Weld;
import org.jboss.weld.environment.se.WeldContainer;

public class MyMain {

    @Inject
    UserManager usermanager;

    public static void main(String[] args) {
        // run everything in a weld container (we need someone who manages our injects)
        Weld weld = new Weld();
        WeldContainer weldContainer = weld.initialize();
        MyMain mymain = weldContainer.instance().select(MyMain.class).get();

        mymain.printUser();
    }

    private void printUser() {
        // Working inject
        System.out.println("Working inject: " + usermanager.getAddress().getStreet() + "\n");

        // Not working inject in the user class
        User myuser = new User("nobody");
        System.out.println("Username: " + myuser.getName() + "\n");

        try {
            Address address = myuser.getAddress();
            String streetname = address.getStreet();
            System.out.println("User Street: " + streetname + "\n");
        } catch (Exception e) {
            System.out.println(e + "\n");
        }

    }

}

这是我的小型测试项目。我的问题是 User 类中的 @Inject 不起作用。在getAddress()函数中，我得到一个java.lang.NullPointerException。但是 MyMain 类中的 @Inject 可以工作。

我已经上传了整个maven项目: http://www.file-upload.net/download-9979514/inject_test.zip.html

使用mvn clean verify运行它

输出是这样的:

[...]
556 [org.inject.test.core.MyMain.main()] WARN org.jboss.weld.interceptor.util.InterceptionTypeRegistry - Class 'javax.ejb.PostActivate' not found, interception based on it is not enabled
556 [org.inject.test.core.MyMain.main()] WARN org.jboss.weld.interceptor.util.InterceptionTypeRegistry - Class 'javax.ejb.PrePassivate' not found, interception based on it is not enabled
Working inject: My test street

Username: nobody

java.lang.NullPointerException

[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO] 
[INFO] test .............................................. SUCCESS [0.739s]
[INFO] test-model ........................................ SUCCESS [2.539s]
[INFO] test-core ......................................... SUCCESS [1.851s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

Answer 1

您的问题在这里:

User myuser = new User("nobody");

您正在创建一个注入(inject)容器不知道的新实例。