XML 通过静态工厂方法注入 Bean

1. 创建一个 User 类和对应的工厂类 UserFactory

User.java

public class User {
    private String name;
    private int age;

    public User() {
        System.out.println("调用User类的无参构造方法");
    }

    public void sayHello(String name){
        System.out.println("hello, " + name + "!");
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

UserFactory.java

public class UserFactory {
    public static User getInstance(){
        return new User();
    }
}

2. 在 Spring 配置文件通过静态工厂方法注入 User 的 Bean

<bean class="org.daistudy.UserFactory" factory-method="getInstance" id="user2"/>

3. 初始化 Spring 的 IoC 容器，并获取 User Bean

User user = (User) context.getBean("user2");
user.sayHello("王五");

4. 适用场景及示例代码

在一些第三方框架适用过程中，无法直接通过普通构造方法注入，则不得不适用静态工厂方式或实例工厂方法注入。例如，在使用 OkHttp 时，由于创建 OkHttpClient 对象时需要先创建一个 Builder 来设置相关属性，此时如果想注入 Bean 则不得不使用静态工厂方法注入。

OkHttpClientFactory.java

public class OkHttpClientFactory {
    public static OkHttpClient getInstance(){
        OkHttpClient okHttpClient = new OkHttpClient
                .Builder()
                .connectTimeout(5, TimeUnit.SECONDS)
                .readTimeout(5, TimeUnit.SECONDS)
                .build();
        return okHttpClient;
    }
}

静态工厂方法注入 OkHttpClient 的 Bean

<bean class="org.daistudy.OkHttpClientFactory" factory-method="getInstance" id="okHttpClient"/>

应用，下载一个图片

public class DownloadImage {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        OkHttpClient okHttpClient = (OkHttpClient) context.getBean("okHttpClient");

        Request request = new Request.Builder().url("http://pic.netbian.com/uploads/allimg/180826/113958-153525479855be.jpg").get().build();
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                // save image
                if (response.isSuccessful()) {
                    InputStream inputStream = response.body().byteStream();
                    FileOutputStream fileOutputStream = new FileOutputStream(new File("E:\\1.png"));
                    byte[] buf = new byte[1024];
                    int len = 0;
                    while((len = inputStream.read(buf)) != -1){
                        fileOutputStream.write(buf, 0, len);
                        fileOutputStream.flush();
                    }
                    fileOutputStream.close();
                    inputStream.close();
                }
            }
        });
    }
}