使用静态实例化方法在生成器类中自动连接依赖项

假设:

1. ArticleBuilder和ArticleMD5HashCalculator之间存在一对一的关系。这意味着您不打算在项目中的不同位置将hashCalculator的不同实例注入ArticleBuilder(基本上有多个ArticleBuilder实例)

您可以按如下方式更改ArticleBuilder impl

public class ArticleBuilder {

    private ArticleMD5HashCalculator hashCalculator;

    public ArticleBuilder(ArticleMD5HashCalculator hashCalculator) { 
        this.hashCalculator = hashCalculator;
    }
}

您可以创建类型为的SpringBean ArticleMD5HashCalculator 把它注射到一个 ArticleBuilder

@Configuration
public class ArticleConfig {

    @Bean
    public ArticleMD5HashCalculator articleMD5HashCalculator() {
        return new ArticleMD5HashCalculator(new MD5HashCalculator());
    }

    @Bean
    public ArticleBuilder() {
        return new ArticleBuilder(articleMD5HashCalculator());
    }
}

你可以自动连线 ArticleBuilder公司 并将其用作生成器。

更新1:

ArticleBuilder公司 在一个 Scraper 对象,并且您希望有一种获取新实例的方法 ArticleBuilder公司 每一次。你可以用弹簧 @Lookup 注释。

的存根实现 刮刀 班

public class Scraper {


    //assuming this is the method where you want to use ArticleBuilder
    public void scrape() {
        getArticleBuilder();
    }

    //You can even pass constructor arguments to this method. 
    //They will be used to match a constructor on the target bean and that gets invoked
    @Lookup
    public ArticleBuilder getArticleBuilder() {
        //Spring creates a runtime implementation of this method.
        return null;
    }
}

getArticleBuilder 只要你想要一个新的bean实例。如果它被声明为prototype,您将始终获得bean的新实例。

但唯一需要注意的是,查找注释不适用于使用创建的bean @Bean 注释。你可能看起来像这样。

@Component
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
public class ArticleBuilder {

    @Autowired
    private ArticleMD5HashCalculator hashCalculator;

    public ArticleBuilder(ArticleMD5HashCalculator hashCalculator) { 
        this.hashCalculator = hashCalculator;
    }
}

@Component
public class ArticleMD5HashCalculator {

    public ArticleMD5HashCalculator(MD5HashCalculator hashCalculator) {
        this.hashCalculator = hashCalculator;
    }
}

beans.xml:

<beans>
    <bean class="MD5HashCalculator" /> 
    <!-- Fully qualified class name is needed -->
</beans>

此外,由于Spring文档中使用的约定,请尽可能使用基于构造函数的注入。

Spring团队通常提倡构造函数注入,因为它使人们能够将应用程序组件实现为不可变对象,并确保所需的依赖项不为空。

完整信息(滚动一点): Spring DOCS

我想出了另一种方法来解决 new '并打开注入模拟的窗口。该解决方案意味着生成器必须由工厂实例化和重新创建。

import org.observer.media.hash.ArticleHashCalculator;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.time.ZonedDateTime;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

@Component
public class ArticleBuilderFactory {

    private ArticleHashCalculator articleHashCalculator;

    @Autowired
    public ArticleBuilderFactory(ArticleHashCalculator articleHashCalculator) {
        this.articleHashCalculator = articleHashCalculator;
    }

    public ArticleBuilder create() {
        return new ArticleBuilder(articleHashCalculator);
    }

    public class ArticleBuilder {

        private ArticleHashCalculator articleHashCalculator;

        private String headline;
        private String subheading;
        //...

        private ArticleBuilder(ArticleHashCalculator articleHashCalculator) {
            this.articleHashCalculator = articleHashCalculator;
        }

        public ArticleBuilderFactory.ArticleBuilder withIndex(int index) {
            this.index = index;
            return this;
        }

        public ArticleBuilderFactory.ArticleBuilder withHeadline(String headline) {
            this.headline = headline;
            return this;
        }
        //...

        public Article build() {
            return new Article(headline, subheading, lead, body, images, quotations, subArticles, url, calculateHash(), author, sources, category, subjects, index, medium, company, datePublished, dateFetched);
        }

        private String calculateHash() {
            return articleHashCalculator.hash(headline, subheading, lead, body, quotations, datePublished, dateFetched);
        }
    }
}

工厂使用:

import org.junit.Test;
import org.junit.runner.RunWith;
import org.observer.media.hash.ArticleMD5HashCalculator;
import org.observer.media.hash.MD5HashCalculator;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringRunner;

import static org.assertj.core.api.Java6Assertions.assertThat;

@RunWith(SpringRunner.class)
@ContextConfiguration(classes = {
        ArticleBuilderFactory.class,
        MD5HashCalculator.class,
        ArticleMD5HashCalculator.class
})
public class ArticleBuilderFactoryTest {

    private static final String HEADLINE = "headline";
    private static final String LEAD = "lead";
    private static final String BODY = "body";

    @Autowired
    private ArticleBuilderFactory articleBuilderFactory;
    @Autowired
    private ArticleMD5HashCalculator hashCalculator;

    @Test
    public void build() {
        ArticleBuilderFactory.ArticleBuilder articleBuilder = articleBuilderFactory.create();
        Article article = articleBuilder
                .withHeadline(HEADLINE)
                .withLead(LEAD)
                .withBody(BODY)
                .build();

        assertThat(article.getHeadline()).isEqualTo(HEADLINE);
        assertThat(article.getLead()).isEqualTo(LEAD);
        assertThat(article.getBody()).isEqualTo(BODY);
        assertThat(article.getHash()).isEqualTo(hashCalculator.hash(HEADLINE, null, LEAD, BODY, null, null, null));
    }
}

@Component
public class ArticleMD5HashCalculator {
}