Spring 资源加载器 分析Spring框架之设计与实现资源加载器

public interface Resource {

    InputStream getInputStream() throws IOException;

}

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;
    }
}

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;
    }

}

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;
        }
    }

}

public interface ResourceLoader {

    /**
     * Pseudo URL prefix for loading from the class path: "classpath:"
     */
    String CLASSPATH_URL_PREFIX = "classpath:";

    Resource getResource(String location);

}

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);
            }
        }
    }

}

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;

}

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;
    }

}

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);
        }
    }

}

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);
    }

}

public class UserService {

    private String uId;

    private UserDao userDao;

    public void queryUserInfo() {
        return userDao.queryUserName(uId);
    }

    // ...get/set
}

<?xml version="1.0" encoding="UTF-8"?>
<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>

private DefaultResourceLoader resourceLoader;      

@Before
public void init() {
    resourceLoader = new DefaultResourceLoader();
}   

@Test
public void test_classpath() throws IOException {
    Resource resource = resourceLoader.getResource("classpath:important.properties");
    InputStream inputStream = resource.getInputStream();
    String content = IoUtil.readUtf8(inputStream);
    System.out.println(content);
}   

@Test
public void test_file() throws IOException {
    Resource resource = resourceLoader.getResource("src/test/resources/important.properties");
    InputStream inputStream = resource.getInputStream();
    String content = IoUtil.readUtf8(inputStream);
    System.out.println(content);
}    

@Test
public void test_url() throws IOException {
    Resource resource = resourceLoader.getResource("https://github.com/fuzhengwei/small-spring/important.properties"
    InputStream inputStream = resource.getInputStream();
    String content = IoUtil.readUtf8(inputStream);
    System.out.println(content);
}

@Test
public void test_xml() {
    // 1.初始化 BeanFactory
    DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();

    // 2. 读取配置文件&注册Bean
    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);
    reader.loadBeanDefinitions("classpath:spring.xml");

    // 3. 获取Bean对象调用方法
    UserService userService = beanFactory.getBean("userService", UserService.class);
    String result = userService.queryUserInfo();
    System.out.println("测试结果：" + result);
}