Small Spring系列七：annotation Injection(三)

秋水共长天一色落霞与孤鹜齐飞。

概述

前两章我们已经完成了使用ASM读取Annotation、新增SimpleMetadataReader封装了复杂的Vister、同时引入了AnnotatedBeanDefinition和ScannedGenericBeanDefinition表明注解扫描的BeanDefinition。本章我们来实现最后的Field Injection。

分析

@Component(value = "nioCoder")
public class NioCoderService {

    @Autowired
    private AccountDao accountDao;

    @Autowired
    private ItemDao itemDao;
}

要实现Field Injection 我们需要根据class类型从BeanFactory中获取一个对象然后注入。即需要在BeanFactory新增一个BeanFactory.resolveDepency(Class type)方法,如果type为AccountDao则找到(或创建)对应的实例并且返回。

这么一看，貌似是可行的,但我们在使用Spring的@Autowired注解时发现，该注解可以应用于构造器注入、属性注入和setter注入。spring提供了一个DependencyDescriptor来封装@Autowired所有情况。

再有我们确定要把resolveDependency方法放置到BeanFactory中吗？BeanFactory是我们的一个顶级接口，我们不希望对外暴露太多的方法,所以我们新增一个AutowireCapableBeanFactory接口,在AutowireCapableBeanFactory中增加resolveDependency方法。AutowireCapableBeanFactory继承BeanFactory。

DependencyDescriptor

封装@Autowired所有情况。(暂只支持字段注入,不支持方法注入)

package com.niocoder.beans.factory.config;

import java.lang.reflect.Field;

/**
 * 表明属性注入或者方法注入
 *
 * @author zhenglongfei
 */
public class DependencyDescriptor {
    /**
     * 属性注入
     */
    private Field field;
    /**
     * 方法注入
     */
//    private MethodParameter methodParameter;

    private boolean required;

    public DependencyDescriptor(Field field, boolean required) {
        this.field = field;
        this.required = required;
    }

    public Class<?> getDependencyType() {
        if (this.field != null) {
            // 字段的类型如 AccountDao ItemDao
            return field.getType();
        }
        // TODO 方法注入不支持
        throw new RuntimeException("only support field dependency");
    }

    public boolean isRequired() {
        return this.required;
    }
}

AutowireCapableBeanFactory

增加resolveDependency(DependencyDescriptor descriptor)方法,根据field返回对应的实例。

package com.niocoder.beans.factory.config;

import com.niocoder.beans.factory.BeanFactory;

/**
 * 表明注解 注入的beanFactory
 */
public interface AutowireCapableBeanFactory extends BeanFactory {

    /**
     * 根据字段属性的描述，获得所对应的实例
     *
     * @param descriptor
     * @return
     */
    Object resolveDependency(DependencyDescriptor descriptor);
}

DefaultBeanFactory

由实现BeanFactory改成实现AutowireCapableBeanFactory。

public class DefaultBeanFactory extends DefaultSingletonBeanRegistry implements AutowireCapableBeanFactory, BeanDefinitionRegistry {

......
    @Override
    public Object resolveDependency(DependencyDescriptor descriptor) {
        Class<?> typeToMatch = descriptor.getDependencyType();
        for (BeanDefinition bd : this.beanDefinitionMap.values()) {
            // 确保BeanDefinition 有Class对象,而不是class的字符串
            resolveBeanClass(bd);
            Class<?> beanClass = bd.getBeanClass();
            if (typeToMatch.isAssignableFrom(beanClass)) {
                return this.getBean(bd.getId());
            }
        }
        return null;
    }

    public void resolveBeanClass(BeanDefinition bd) {
        if (bd.hasBeanClass()) {
            return;
        } else {
            try {
                bd.resolveBeanClass(ClassUtils.getDefaultClassLoader());
            } catch (ClassNotFoundException e) {
                throw new RuntimeException("can't load class" + bd.getBeanClassName());
            }
        }
    }

......

}

GenericBeanDefinition

新增beanClass属性,缓存bean的class对象

public class GenericBeanDefinition implements BeanDefinition {

    private Class<?> beanClass;
......
    @Override
    public Class<?> getBeanClass() {
        if (this.beanClass == null) {
            throw new IllegalStateException("Bean class name [" + this.getBeanClassName() + "] has not been resolve into an actual Class");
        }
        return this.beanClass;
    }
    @Override
    public boolean hasBeanClass() {
        return this.beanClass != null;
    }

    @Override
    public Class<?> resolveBeanClass(ClassLoader beanClassLoader) throws ClassNotFoundException {
        String className = getBeanClassName();
        if (className == null) {
            return null;
        }
        Class<?> resolvedClass = beanClassLoader.loadClass(className);
        this.beanClass = resolvedClass;
        return resolvedClass;
    }

}

DependencyDescriptorTest

测试DependencyDescriptor

/**
 * 测试DependencyDescriptor
 */
public class DependencyDescriptorTest {

    @Test
    public void testResolveDependency() throws Exception {
        DefaultBeanFactory factory = new DefaultBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
        reader.loadBeanDefinition(new ClassPathResource("bean-v4.xml"));

        Field f = NioCoderService.class.getDeclaredField("accountDao");
        DependencyDescriptor descriptor = new DependencyDescriptor(f, true);
        Object o = factory.resolveDependency(descriptor);
        Assert.assertTrue(o instanceof AccountDao);

    }
}

代码下载

github:https://github.com/longfeizheng/small-spring/tree/20190202_annotation_v5

Field Injection

上面我们已经可以通过class类型来获取bean的实例了，那么怎么才能实现自动注入呢？

首先我们需要一个类含有targetClass和一个集合的属性列表List<Class>,每个集合中的元素调用各自的inject(taget)方法(反射)从而实现属性注入。类图如下:

InjectionElement

抽象类,表明需要注入的属性字段

package com.niocoder.beans.factory.annotation;

import com.niocoder.beans.factory.config.AutowireCapableBeanFactory;

import java.lang.reflect.Member;

/**
 * @author zhenglongfei
 */
public abstract class InjectionElement {

    protected Member member;
    protected AutowireCapableBeanFactory factory;

    InjectionElement(Member member, AutowireCapableBeanFactory factory) {
        this.member = member;
        this.factory = factory;
    }

    /**
     * 属性注入的抽象方法
     *
     * @param target
     */
    public abstract void inject(Object target);
}

AutowiredFieldElement

继承抽象类InjectionElement实现属性注入

package com.niocoder.beans.factory.annotation;

import com.niocoder.beans.factory.BeanCreationException;
import com.niocoder.beans.factory.config.AutowireCapableBeanFactory;
import com.niocoder.beans.factory.config.DependencyDescriptor;
import com.niocoder.util.*;

import java.lang.reflect.Field;


/**
 * @author zhenglongfei
 */
public class AutowiredFieldElement extends InjectionElement {

    boolean required;

    public AutowiredFieldElement(Field f, boolean required, AutowireCapableBeanFactory factory) {
        super(f, factory);
        this.required = required;
    }

    public Field getField() {
        return (Field) this.member;
    }

    @Override
    public void inject(Object target) {
        Field field = this.getField();

        try {
            DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
            Object value = factory.resolveDependency(desc);
            if (value != null) {
                ReflectionUtils.makeAccessible(field);
                field.set(target, value);
            }
        } catch (Throwable e) {
            throw new BeanCreationException("could not autowire field " + field, e);
        }
    }
}

InjectionMetadata

将targetClass和List<InjectionElement>结合,从而实现属性注入

package com.niocoder.beans.factory.annotation;

import java.util.List;

/**
 * @author zhenglongfei
 */
public class InjectionMetadata {

    private final Class<?> targetClass;
    private List<InjectionElement> injectionElements;

    public InjectionMetadata(Class<?> targetClass, List<InjectionElement> injectionElements) {
        this.targetClass = targetClass;
        this.injectionElements = injectionElements;
    }

    public List<InjectionElement> getInjectionElements() {
        return injectionElements;
    }

    public void inject(Object target) {
        if (injectionElements == null || injectionElements.isEmpty()) {
            return;
        }
        for (InjectionElement ele : injectionElements) {
            ele.inject(target);
        }
    }
}

InjectionMetadataTest

测试属性注入

package com.niocoder.test.v4;

import com.niocoder.beans.factory.annotation.AutowiredFieldElement;
import com.niocoder.beans.factory.annotation.InjectionElement;
import com.niocoder.beans.factory.annotation.InjectionMetadata;
import com.niocoder.beans.factory.support.DefaultBeanFactory;
import com.niocoder.beans.factory.xml.XmlBeanDefinitionReader;
import com.niocoder.core.io.ClassPathResource;
import com.niocoder.dao.v4.AccountDao;
import com.niocoder.dao.v4.ItemDao;
import com.niocoder.service.v4.NioCoderService;
import org.junit.Assert;
import org.junit.Test;

import java.lang.reflect.Field;
import java.util.LinkedList;


public class InjectionMetadataTest {

    @Test
    public void testInjection() throws Exception {
        DefaultBeanFactory factory = new DefaultBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
        reader.loadBeanDefinition(new ClassPathResource("bean-v4.xml"));

        Class<?> clz = NioCoderService.class;

        LinkedList<InjectionElement> elements = new LinkedList<InjectionElement>();

        {
            Field f = NioCoderService.class.getDeclaredField("accountDao");
            InjectionElement injectionElement = new AutowiredFieldElement(f, true, factory);
            elements.add(injectionElement);
        }

        {
            Field f = NioCoderService.class.getDeclaredField("itemDao");
            InjectionElement injectionElement = new AutowiredFieldElement(f, true, factory);
            elements.add(injectionElement);
        }

        InjectionMetadata metadata = new InjectionMetadata(clz, elements);
        NioCoderService nioCoderService = new NioCoderService();
        metadata.inject(nioCoderService);

        Assert.assertTrue(nioCoderService.getAccountDao() instanceof AccountDao);

        Assert.assertTrue(nioCoderService.getItemDao() instanceof ItemDao);
    }
}

代码下载

github:https://github.com/longfeizheng/small-spring/tree/20190202_annotation_v6

自动构建InjectionMetadata

以上我们只是通过手动的将NioCoderService转变成了InjectionMetadata并且调用inject方法,从而实现了Field Injection,我们需要一个类来自动帮我们处理这些操作。

AutowiredAnnotationBeanPostProcessor

用于自动构建InjectionMetadata

public class AutowiredAnnotationBeanPostProcessor{

    private AutowireCapableBeanFactory beanFactory;
    private String requiredParameterName = "required";
    private boolean requiredParameterValue = true;

    /**
     * 存储需要判断的注解信息
     */
    private final Set<Class<? extends Annotation>> autowiredAnnotationTypes = new LinkedHashSet<>();

    /**
     * 添加Autowired注解
     */
    public AutowiredAnnotationBeanPostProcessor() {
        this.autowiredAnnotationTypes.add(Autowired.class);
    }

    /**
     * 给定class对象构建InjectionMetadata
     * @param clazz
     * @return
     */
    public InjectionMetadata buildAutowiringMetadata(Class<?> clazz) {
        List<InjectionElement> elements = new LinkedList<>();
        Class<?> targetClass = clazz;

        do {
            List<InjectionElement> currElements = new LinkedList<>();
            for (Field field : targetClass.getDeclaredFields()) {
                Annotation ann = findAutowiredAnnotation(field);
                if (ann != null) {
                    if (Modifier.isStatic(field.getModifiers())) {
                        continue;
                    }
                    boolean required = determineRequiredStatus(ann);
                    currElements.add(new AutowiredFieldElement(field, required, beanFactory));
                }
            }

            for (Method method : targetClass.getDeclaredMethods()) {
                //TODO
            }
            elements.addAll(0, currElements);
            targetClass = targetClass.getSuperclass();
        } while (targetClass != null && targetClass != Object.class);

        return new InjectionMetadata(clazz, elements);
    }

    /**
     * 判断是否是required是否必须
     *
     * @param ann
     * @return
     */
    private boolean determineRequiredStatus(Annotation ann) {
        try {
            Method method = ReflectionUtils.findMethod(ann.annotationType(), this.requiredParameterName);
            if (method == null) {
                // Annotations like @Inject and @Value don't have a method (attribute) named "required"
                // -> default to required status
                return true;
            }
            return (this.requiredParameterValue == (Boolean) ReflectionUtils.invokeMethod(method, ann));
        } catch (Exception ex) {
            // An exception was thrown during reflective invocation of the required attribute
            // -> default to required status
            return true;
        }
    }

    /**
     * 判断属性是否存在Autowired 注解
     *
     * @param field
     * @return
     */
    private Annotation findAutowiredAnnotation(Field field) {
        for (Class<? extends Annotation> type : this.autowiredAnnotationTypes) {
            Annotation ann = AnnotationUtils.getAnnotation(field, type);
            if (ann != null) {
                return ann;
            }
        }
        return null;
    }

    public void setBeanFactory(ConfigurableBeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }
}

AutowiredAnnotationProcessorTest

测试 AutowiredAnnotationProcessor

public class AutowiredAnnotationProcessorTest {

    AccountDao accountDao = new AccountDao();
    ItemDao itemDao = new ItemDao();

    DefaultBeanFactory beanFactory = new DefaultBeanFactory() {
        @Override
        public Object resolveDependency(DependencyDescriptor descriptor) {
            if (descriptor.getDependencyType().equals(AccountDao.class)) {
                return accountDao;
            }

            if (descriptor.getDependencyType().equals(ItemDao.class)) {
                return itemDao;
            }
            throw new RuntimeException("can't support types except AccountDao and ItemDao");
        }
    };

    @Test
    public void testGetInjectionMetadata() {
        AutowiredAnnotationBeanPostProcessor processor = new AutowiredAnnotationBeanPostProcessor();
        processor.setBeanFactory(beanFactory);
        InjectionMetadata injectionMetadata = processor.buildAutowiringMetadata(NioCoderService.class);
        List<InjectionElement> elements = injectionMetadata.getInjectionElements();
        Assert.assertEquals(2, elements.size());

        assertFieldExists(elements,"accountDao");
        assertFieldExists(elements,"itemDao");

        NioCoderService nioCoderService = new NioCoderService();
        injectionMetadata.inject(nioCoderService);

        Assert.assertTrue(nioCoderService.getAccountDao() instanceof AccountDao);

        Assert.assertTrue(nioCoderService.getItemDao() instanceof ItemDao);
    }

    private void assertFieldExists(List<InjectionElement> elements, String fieldName) {
        for (InjectionElement ele : elements) {
            AutowiredFieldElement fieldElement = (AutowiredFieldElement) ele;
            Field field = fieldElement.getField();
            if (field.getName().equals(fieldName)) {
                return;
            }
        }
        Assert.fail(fieldName + "does not exist!");
    }
}

完善Field Injection

至此我们已经完成了Field Injection90%的工作,剩下要考虑的就是应该在什么时候调用类的这些方法？

所以我们要考虑一下bean的生命周期,关于bean的生命周期,可以看下图

参考Bean的生命周期

我们需要找InstantiationAwareBeanPostProcessor.postProcessPropertyValues()实现Autowired注解。关于BeanPostProcessor的类图如下:

BeanPostProcessor

bean初始化之前和初始化之后的处理器操作

package com.niocoder.beans.factory.config;

import com.niocoder.beans.BeansException;

/**
 * bean的后置处理器
 *
 * @author zhenglongfei
 */
public interface BeanPostProcessor {

    /**
     * 初始化之前的操作
     *
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    /**
     * 初始化之后的操作
     *
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

InstantiationAwareBeanPostProcessor

bean实例化之前和实例化之后的处理器操作

package com.niocoder.beans.factory.config;

import com.niocoder.beans.BeansException;

/**
 * 实例化的后处理器
 *
 * @author zhenglongfei
 */
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

    /**
     * 实例化之前
     *
     * @param beanClass
     * @param beanName
     * @return
     * @throws BeansException
     */
    default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        return null;
    }

    /**
     * 实例化之后
     *
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        return true;
    }

    /**
     * @param bean
     * @param beanName
     * @throws BeansException
     */
    default void postProcessPropertyValues(Object bean, String beanName) throws BeansException {
    }

}

AutowiredAnnotationBeanPostProcessor

实现InstantiationAwareBeanPostProcessor,在postProcessPropertyValues方法实现属性注入

/**
 * 注解注入的后处理器
 *
 * @author zhenglongfei
 */
public class AutowiredAnnotationBeanPostProcessor implements InstantiationAwareBeanPostProcessor {

......
    @Override
    public void postProcessPropertyValues(Object bean, String beanName) throws BeansException {
        InjectionMetadata metadata = buildAutowiringMetadata(bean.getClass());
        try {
            metadata.inject(bean);
        } catch (Throwable ex) {
            throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
        }
    }
}

ConfigurableBeanFactory

新增ConfigurableBeanFactory来处理BeanPostProcessor

package com.niocoder.beans.factory.config;

import java.util.List;

/**
 * 可配置的beanFactory
 *
 * @author zhenglongfei
 */
public interface ConfigurableBeanFactory extends AutowireCapableBeanFactory {

    /**
     * 增加BeanPostProcessor
     *
     * @param postProcessor
     */
    void addBeanPostProcessor(BeanPostProcessor postProcessor);

    /**
     * 获取 BeanPostProcessor
     *
     * @return
     */
    List<BeanPostProcessor> getBeanPostProcessors();
}

DefaultBeanFactory

DefaultBeanFactory从实现AutowireCapableBeanFactory修改为ConfigurableBeanFactory,增加 beanPostProcessors属性, 在populateBean方法时处理BeanPostProcessor。

/**
 * BeanFactory的默认实现类
 *
 * @author zhenglongfei
 */
public class DefaultBeanFactory extends DefaultSingletonBeanRegistry implements ConfigurableBeanFactory, BeanDefinitionRegistry {

    /**
     * 存放BeanPostProcessor
     */
    private List<BeanPostProcessor> beanPostProcessors = new ArrayList<>();


    private void populateBean(BeanDefinition bd, Object bean) {

        for (BeanPostProcessor postProcessor : this.getBeanPostProcessors()) {
            if (postProcessor instanceof InstantiationAwareBeanPostProcessor) {
                ((InstantiationAwareBeanPostProcessor) postProcessor).postProcessPropertyValues(bean, bd.getId());
            }
        }
		......
	}
    @Override
    public void addBeanPostProcessor(BeanPostProcessor postProcessor) {
        this.beanPostProcessors.add(postProcessor);
    }

    @Override
    public List<BeanPostProcessor> getBeanPostProcessors() {
        return this.beanPostProcessors;
    }
}

AbstractApplicationContext

构造方法时注册AutowiredAnnotationBeanPostProcessor实现注解注入

public abstract class AbstractApplicationContext implements ApplicationContext {

    private DefaultBeanFactory factory = null;

    public AbstractApplicationContext(String configFile) {
        factory = new DefaultBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
        Resource resource = this.getResourceByPath(configFile);
        reader.loadBeanDefinition(resource);
        registerBeanPostProcessors(factory);
    }

    /**
     * 具体由子类实现
     *
     * @param configFile
     * @return
     */
    protected abstract Resource getResourceByPath(String configFile);

    @Override
    public Object getBean(String beanId) {
        return factory.getBean(beanId);
    }

    protected void registerBeanPostProcessors(ConfigurableBeanFactory beanFactory) {
        AutowiredAnnotationBeanPostProcessor processor = new AutowiredAnnotationBeanPostProcessor();
        processor.setBeanFactory(factory);
        beanFactory.addBeanPostProcessor(processor);
    }
}

ApplicationContextTestV4

测试注解注入

/**
 *
 */
public class ApplicationContextTestV4 {

    @Test
    public void testGetBeanProperty() {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("bean-v4.xml");
        NioCoderService nioCoder = (NioCoderService) ctx.getBean("nioCoder");

        Assert.assertNotNull(nioCoder.getAccountDao());
        Assert.assertNotNull(nioCoder.getItemDao());
    }
}

代码下载

github:https://github.com/longfeizheng/small-spring/tree/20190211_annotation_v7

代码下载

github:https://github.com/longfeizheng/small-spring

参考资料

从零开始造Spring

我的技术知识分享

Small Spring系列七：annotation Injection(三)

概述

分析

DependencyDescriptor

AutowireCapableBeanFactory

DefaultBeanFactory

GenericBeanDefinition

DependencyDescriptorTest

代码下载

Field Injection

InjectionElement

AutowiredFieldElement

InjectionMetadata

InjectionMetadataTest

代码下载

自动构建InjectionMetadata

AutowiredAnnotationBeanPostProcessor

AutowiredAnnotationProcessorTest

完善Field Injection

BeanPostProcessor

InstantiationAwareBeanPostProcessor

AutowiredAnnotationBeanPostProcessor

ConfigurableBeanFactory

DefaultBeanFactory

AbstractApplicationContext

ApplicationContextTestV4

代码下载

代码下载

参考资料

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