mini-spring|设计与实现资源加载器并从Spring.xml解析和注册Bean对象

**需求：**我们需要自动为bean加载资源，代替注册、注入属性、注入bean等功能

1.资源加载器属于相对独立的部分，它位于 Spring 框架核心包下的IO实现内容，主要用于处理Class、本地和云环境中的文件信息。

2.当资源可以加载后，接下来就是解析和注册 Bean 到 Spring 中的操作，这部分实现需要和DefaultListableBeanFactory 核心类结合起来，因为你所有的解析后的注册动作，都会把 Bean 定义信息放入到这个类中。

3.那么在实现的时候就设计好接口的实现层级关系，包括我们需要定义出 Bean 定义的读取接口BeanDefinitionReader 以及做好对应的实现类，在实现类中完成对 Bean 对象的解析和注册。

Resource

在 Spring 框架下创建 core.io 核心包，在这个包中主要用于处理资源加载流。定义 Resource 接口，提供获取 InputStream 流的方法，接下来再分别实现三种不同的流文件操作：classPath、FileSystem、URL

public interface Resource {

    InputStream getInputStream() throws IOException;

}

ClassPath

该函数实现是用于通过 ClassLoader 读取ClassPath 下的文件信息，具体的读取过程主要是：classLoader.getResourceAsStream(path)

public class ClassPathResource implements Resource {

    private final String path;

    private ClassLoader classLoader;

    public ClassPathResource(String path) {
        this(path, (ClassLoader) null);
    }

    public ClassPathResource(String path, ClassLoader classLoader) {
        Assert.notNull(path, "Path must not be null");
        this.path = path;
        this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
    }

    @Override
    public InputStream getInputStream() throws IOException {
        InputStream is = classLoader.getResourceAsStream(path);
        if (is == null) {
            throw new FileNotFoundException(
                    this.path + " cannot be opened because it does not exist");
        }
        return is;
    }
}

FileSystemResource

通过指定文件路径的方式读取文件信息，这部分大家肯定还是非常熟悉的，经常会读取一些txt、excel文件输出到控制台

public class FileSystemResource implements Resource {
    private final File file;
    private final String path;
    public FileSystemResource(File file) {
        this.file = file;
        this.path = file.getPath();
    }
    public FileSystemResource(String path) {
        this.file = new File(path);
        this.path = path;
    }
    @Override
    public InputStream getInputStream() throws IOException {
        return new FileInputStream(this.file);
    }
    public final String getPath() {
        return this.path;
    }
}

UrlResource

通过 HTTP 的方式读取云服务的文件，我们也可以把配置文件放到 GitHub 或者 Gitee 上

public class UrlResource implements Resource{
    private final URL url;
    public UrlResource(URL url) {
        Assert.notNull(url,"URL must not be null");
        this.url = url;
    }
    @Override
    public InputStream getInputStream() throws IOException {
        URLConnection con = this.url.openConnection();
        try {
            return con.getInputStream();
        }
        catch (IOException ex){
            if (con instanceof HttpURLConnection){
                ((HttpURLConnection) con).disconnect();
            }
            throw ex;
        }
    }
}

ResourceLoader

ResourceLoader用于继承不同方式的资源加载

public interface ResourceLoader {
    String CLASSPATH_URL_PREFIX = "classpath:";
    Resource getResource(String location);
}

实现接口DefaultResourceLoader

public class DefaultResourceLoader implements ResourceLoader {
    @Override
    public Resource getResource(String location) {
        Assert.notNull(location, "Location must not be null");
        if (location.startsWith(CLASSPATH_URL_PREFIX)) {
            return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()));
        }
        else {
            try {
                URL url = new URL(location);
                return new UrlResource(url);
            } catch (MalformedURLException e) {
                return new FileSystemResource(location);
            }
        }
    }
}

Bean定义读取接口 BeanDefinitionReader

getRegistry()、getResourceLoader()，都是用于提供给后面三个loadBeanDefinitions方法的工具，用于bean的注册和资源加载

public interface BeanDefinitionReader {

    BeanDefinitionRegistry getRegistry();

    ResourceLoader getResourceLoader();

    void loadBeanDefinitions(Resource resource) throws BeansException;

    void loadBeanDefinitions(Resource... resources) throws BeansException;

    void loadBeanDefinitions(String location) throws BeansException;

}

bean定义抽象类实现接口

AbstractBeanDefinitionReader

public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader {

    private final BeanDefinitionRegistry registry;

    private ResourceLoader resourceLoader;

    protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {
        this(registry, new DefaultResourceLoader());
    }

    public AbstractBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        this.registry = registry;
        this.resourceLoader = resourceLoader;
    }

    @Override
    public BeanDefinitionRegistry getRegistry() {
        return registry;
    }

    @Override
    public ResourceLoader getResourceLoader() {
        return resourceLoader;
    }

}

抽象类把 BeanDefinitionReader 接口的getRegistry、getResourceLoader两个方法全部实现完了，并提供了构造函数，让外部的调用使用方

这样在接口 BeanDefinitionReader 的具体实现类中，就可以把解析后的 XML 文件中的 Bean 信息，注册到 Spring 容器去了。

解析XML处理Bean注册

XmlBeanDefinitionReader

public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
        super(registry);
    }

    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry, ResourceLoader resourceLoader) {
        super(registry, resourceLoader);
    }

    @Override
    public void loadBeanDefinitions(Resource resource) throws BeansException {
        try {
            try (InputStream inputStream = resource.getInputStream()) {
                doLoadBeanDefinitions(inputStream);
            }
        } catch (IOException | ClassNotFoundException e) {
            throw new BeansException("IOException parsing XML document from " + resource, e);
        }
    }

    @Override
    public void loadBeanDefinitions(Resource... resources) throws BeansException {
        for (Resource resource : resources) {
            loadBeanDefinitions(resource);
        }
    }

    @Override
    public void loadBeanDefinitions(String location) throws BeansException {
        ResourceLoader resourceLoader = getResourceLoader();
        Resource resource = resourceLoader.getResource(location);
        loadBeanDefinitions(resource);
    }

    protected void doLoadBeanDefinitions(InputStream inputStream) throws ClassNotFoundException {
        Document doc = XmlUtil.readXML(inputStream);
        Element root = doc.getDocumentElement();
        NodeList childNodes = root.getChildNodes();

        for (int i = 0; i < childNodes.getLength(); i++) {
            // 判断元素
            if (!(childNodes.item(i) instanceof Element)) continue;
            // 判断对象
            if (!"bean".equals(childNodes.item(i).getNodeName())) continue;
            // 解析标签
            Element bean = (Element) childNodes.item(i);
            String id = bean.getAttribute("id");
            String name = bean.getAttribute("name");
            String className = bean.getAttribute("class");
            // 获取 Class，方便获取类中的名称
            Class<?> clazz = Class.forName(className);
            // 优先级 id > name
            String beanName = StrUtil.isNotEmpty(id) ? id : name;
            if (StrUtil.isEmpty(beanName)) {
                beanName = StrUtil.lowerFirst(clazz.getSimpleName());
            }
            // 定义Bean
            BeanDefinition beanDefinition = new BeanDefinition(clazz);
            // 读取属性并填充
            for (int j = 0; j < bean.getChildNodes().getLength(); j++) {
                if (!(bean.getChildNodes().item(j) instanceof Element)) continue;
                if (!"property".equals(bean.getChildNodes().item(j).getNodeName())) continue;
                // 解析标签：property
                Element property = (Element) bean.getChildNodes().item(j);
                String attrName = property.getAttribute("name");
                String attrValue = property.getAttribute("value");
                String attrRef = property.getAttribute("ref");
                // 获取属性值：引入对象、值对象
                Object value = StrUtil.isNotEmpty(attrRef) ? new BeanReference(attrRef) : attrValue;
                // 创建属性信息
                PropertyValue propertyValue = new PropertyValue(attrName, value);
                beanDefinition.getPropertyValues().addPropertyValue(propertyValue);
            }
            if (getRegistry().containsBeanDefinition(beanName)) {
                throw new BeansException("Duplicate beanName[" + beanName + "] is not allowed");
            }
            // 注册 BeanDefinition
            getRegistry().registerBeanDefinition(beanName, beanDefinition);
        }
    }

}

1.loadBeanDefinitions 方法，处理资源加载，这里新增加了一个内部方法：doLoadBeanDefinitions，它主要负责解析 xml

2.在 doLoadBeanDefinitions 方法中，主要是对xml的读取 XmlUtil.readXML(inputStream) 和元素 Element 解析。在解析的过程中通过循环操作，以此获取 Bean 配置以及配置中的 id、name、class、value、ref 信息 。

3.最终把配置信息创建成 BeanDefinition 以及 PropertyValue ，最终把完整的 Bean 定义内容****注册到 Bean 容器：getRegistry().registerBeanDefinition(beanName, beanDefinition)

测试

UserDao

package cn.bugstack.springframework.test.bean;

import java.util.HashMap;
import java.util.Map;

public class UserDao {

    private static Map<String, String> hashMap = new HashMap<>();

    static {
        hashMap.put("10001", "小傅哥");
        hashMap.put("10002", "八杯水");
        hashMap.put("10003", "阿毛");
    }

    public String queryUserName(String uId) {
        return hashMap.get(uId);
    }

}

UserService

public class UserService {

    private String uId;
    private String company;
    private String location;
    private UserDao userDao;

    public String queryUserInfo() {
        return userDao.queryUserName(uId) + "," + company + "," + location;
    }

    public String getuId() {
        return uId;
    }

    public void setuId(String uId) {
        this.uId = uId;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
}

spring.xml

<beans>

    <bean id="userDao" class="cn.bugstack.springframework.test.bean.UserDao"/>

    <bean id="userService" class="cn.bugstack.springframework.test.bean.UserService">
        <property name="uId" value="10001"/>
        <property name="userDao" ref="userDao"/>
    </bean>

</beans>

    @Test
    public void test_xml() {
        // 1.初始化 BeanFactory
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring.xml");

        // 2. 获取Bean对象调用方法
        UserService userService = applicationContext.getBean("userService", UserService.class);
        String result = userService.queryUserInfo();
        System.out.println("测试结果：" + result);
    }