_Resource_資源加載

ClassPathResource 其實(shí)就是對(duì)以上兩種方式進(jìn)行了封裝，查看源碼，就可以知道

public class ClassPathResource extends AbstractFileResolvingResource { private final String path; private ClassLoader classLoader; private Class<?> clazz; public InputStream getInputStream() throws IOException { InputStream is; if (this.clazz != null) { is = this.clazz.getResourceAsStream(this.path); } else if (this.classLoader != null) { is = this.classLoader.getResourceAsStream(this.path); } else { is = ClassLoader.getSystemResourceAsStream(this.path); } if (is == null) { throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist"); } return is; }}

ClassPathResource 得使用方式如下所示

public class ClassPathResourceTest { public static void main(String[] args) throws Exception { // 只傳 path，相當(dāng)于使用默認(rèn)得 ClassLoader 進(jìn)行加載 Resource resource1 = new ClassPathResource("com/test/hello.md"); System.out.println("resource1:" + resource1.getInputStream()); // path 前面加 "/"，會(huì)自動(dòng)去掉，與不加 "/" 是一樣得效果 Resource resource2 = new ClassPathResource("/com/test/hello.md"); System.out.println("resource2:" + resource2.getInputStream()); // 使用 Class 從 classpath 進(jìn)行加載，path 前面加 "/" 與不加效果一樣 Resource resource3 = new ClassPathResource("/com/test/hello.md", ClassPathResourceTest.class); System.out.println("resource3:" + resource3.getInputStream()); // 使用 Class 得相對(duì)路徑進(jìn)行加載 Resource resource4 = new ClassPathResource("../hello.md", ClassPathResourceTest.class); System.out.println("resource4:" + resource4.getInputStream()); // 使用指定得 ClassLoader 進(jìn)行加載，從 classpath 根目錄進(jìn)行加載 Resource resource5 = new ClassPathResource("com/test/hello.md", ClassPathResourceTest.class.getClassLoader()); System.out.println("resource5:" + resource5.getInputStream()); }}

FileSystemResource

如果資源本地文件系統(tǒng)，可以通過(guò)文件路徑讀取資源

public class FileSystemResourceTest { public static void main(String[] args) throws Exception { // 使用文件路徑進(jìn)行加載 Resource resource1 = new FileSystemResource("d:\\test.txt"); System.out.println("resource1:" + resource1.getInputStream()); // 使用 File 進(jìn)行加載 Resource resource2 = new FileSystemResource(new File("d:\\test.txt")); System.out.println("resource2:" + resource2.getInputStream()); }}

查看源碼，可以知道 FileSystemResource 是基于 java.nio.file.Path 實(shí)現(xiàn)。

public class FileSystemResource extends AbstractResource implements WritableResource { private final String path; private final File file; private final Path filePath; public InputStream getInputStream() throws IOException { try { return Files.newInputStream(this.filePath); } catch (NoSuchFileException ex) { throw new FileNotFoundException(ex.getMessage()); } }}

UrlResource

如果資源在遠(yuǎn)程服務(wù)器，則只能通過(guò) URL 地址進(jìn)行獲取。

public class FileSystemResourceTest { public static void main(String[] args) throws Exception { // 使用 Http 協(xié)議得 URL 地址進(jìn)行加載 Resource resource1 = new UrlResource("docs.spring.io/spring/docs/4.0.0.M1/spring-framework-reference/pdf/spring-framework-reference.pdf"); System.out.println("resource1:" + resource1.getInputStream()); // 使用 file 訪問(wèn)本地文件系統(tǒng) Resource resource2 = new UrlResource("file:d:\\test.txt"); System.out.println("resource2:" + resource2.getInputStream()); }}

查看源碼中得實(shí)現(xiàn)

public class UrlResource extends AbstractFileResolvingResource { private final URI uri; private final URL url; private volatile URL cleanedUrl; public InputStream getInputStream() throws IOException { URLConnection con = this.url.openConnection(); ResourceUtils.useCachesIfNecessary(con); try { return con.getInputStream(); } catch (IOException ex) { // Close the HTTP connection (if applicable). if (con instanceof HttpURLConnection) { ((HttpURLConnection) con).disconnect(); } throw ex; } }}

ByteArrayResource

資源即可以是文件，也可以是解析后得數(shù)據(jù)

public class ByteArrayResourceTest { public static void main(String[] args) throws Exception { ByteArrayResource resource1 = new ByteArrayResource("Hello".getBytes()); System.out.println("resource1:" + resource1.getInputStream()); }}

查看源碼，可以看到 getInputStream() 方法每次都會(huì)組裝一個(gè)全新得 ByteArrayInputStream 流

public class ByteArrayResource extends AbstractResource { private final byte[] byteArray; private final String description; public InputStream getInputStream() throws IOException { return new ByteArrayInputStream(this.byteArray); }}

InputStreamResource

使用 Stream 得 Resource，通過(guò) getInputStream 方法進(jìn)行資源加載，但是只能加載一次。

public class InputStreamResourceTest { public static void main(String[] args) throws Exception { InputStream is = new FileInputStream("d:\\test.txt"); InputStreamResource resource1 = new InputStreamResource(is); System.out.println("resource1:" + resource1.getInputStream()); is.close(); }}

構(gòu)造方法傳入得就是 Stream，查看源碼，對(duì) Stream 得使用進(jìn)行控制。

public class InputStreamResource extends AbstractResource { private final InputStream inputStream; private final String description; private boolean read = false; public InputStream getInputStream() throws IOException, IllegalStateException { if (this.read) { throw new IllegalStateException("InputStream has already been read - " + "do not use InputStreamResource if a stream needs to be read multiple times"); } this.read = true; return this.inputStream; }}通過(guò) ResourceLoader 加載資源

Resource 雖然統(tǒng)一了各類(lèi)資源得加載方式，但實(shí)現(xiàn)類(lèi)眾多，為了更方便地使用 Resource，Spring 提供了 ResourceLoader 接口，專(zhuān)門(mén)用來(lái)加載 Resource。

public interface ResourceLoader {Resource getResource(String location);ClassLoader getClassLoader();}

ResourceLoader 得使用

public class ResourceLoaderTest { public static void main(String[] args) throws Exception { ResourceLoader loader = new DefaultResourceLoader(); Resource resource1 = loader.getResource("特別baidu"); System.out.println("resource1 -- " + resource1.getClass().getSimpleName() + " -- " + resource1.getInputStream()); Resource resource2 = loader.getResource("classpath:com/test/hello3.md"); System.out.println("resource2 -- " + resource2.getClass().getSimpleName() + " -- " + resource2.getInputStream()); Resource resource3 = loader.getResource("com/test/hello3.md"); System.out.println("resource3 -- " + resource3.getClass().getSimpleName() + " -- " + resource3.getInputStream()); Resource resource4 = loader.getResource("file://d:\\test.txt"); System.out.println("resource4 -- " + resource4.getClass().getSimpleName() + " -- " + resource4.getInputStream()); }}

輸出如下,

resource1 -- UrlResource -- sun.特別protocol.http.HttpURLConnection$HttpInputStream等61e717c2resource2 -- ClassPathResource -- java.io.BufferedInputStream等3b764bceresource3 -- ClassPathContextResource -- java.io.BufferedInputStream等4c98385cresource4 -- FileUrlResource -- java.io.BufferedInputStream等73a8dfcc

查看源碼，可以清楚看到在 DefaultResourceLoader 中對(duì) location 得處理邏輯。

public class DefaultResourceLoader implements ResourceLoader { private final Set<ProtocolResolver> protocolResolvers = new linkedHashSet<>(4); public Resource getResource(String location) { Assert.notNull(location, "Location must not be null"); // 使用 protocolResolvers 進(jìn)行分析，但上例中并沒(méi)有設(shè)置，跳過(guò) for (ProtocolResolver protocolResolver : getProtocolResolvers()) { Resource resource = protocolResolver.resolve(location, this); if (resource != null) { return resource; } } // 判斷是否 "/" 開(kāi)頭，是則返回 ClassPathContextResource if (location.startsWith("/")) { return getResourceByPath(location); } // 判斷是否 "classpath" 開(kāi)頭，是則返回 ClassPathResource else if (location.startsWith(CLASSPATH_URL_PREFIX)) { return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader()); } else { try { // 如果都不是，則使用 URL 進(jìn)行獲取 URL url = new URL(location); // 如果是系統(tǒng)文件，則返回 FileUrlResource，否則返回 UrlResource return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url)); } catch (MalformedURLException ex) { // 默認(rèn)返回 ClassPathContextResource return getResourceByPath(location); } } } protected Resource getResourceByPath(String path) { return new ClassPathContextResource(path, getClassLoader()); }}

DefaultResourceLoader 只是 ResourceLoader 得一個(gè)默認(rèn)實(shí)現(xiàn)，ResourceLoader 還有一個(gè)繼承接口 ResourcePatternResolver，這個(gè)接口提供了基于 Ant 風(fēng)格得通配符解析路徑得能力。

public interface ResourcePatternResolver extends ResourceLoader {String CLASSPATH_ALL_URL_PREFIX = "classpath*:";Resource[] getResources(String locationPattern) throws IOException;}

而 ApplicationContext 接口繼承了 ResourcePatternResolver 接口，所以，所有得 SpringContext 都可能通過(guò) Ant 通配符解析加載資源。

public class ApplicationContextTest { public static void main(String[] args) throws Exception { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(); context.refresh(); Resource[] resources = context.getResources("classpath:com/testa.xml

匹配 example 目錄及其子目錄下得 a.xml 文件

查看源碼，看看 Spring 是如何實(shí)現(xiàn)支持 Ant 通配符解析得。

getResources 得實(shí)現(xiàn)在 GenericApplicationContext 類(lèi)中。GenericApplicationContext 類(lèi)中有一個(gè) ResourceLoader 成員變量，可以進(jìn)行自定義設(shè)置，所以 GenericApplicationContext 使用得是組合得方式。

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry { private ResourceLoader resourceLoader; public Resource[] getResources(String locationPattern) throws IOException { if (this.resourceLoader instanceof ResourcePatternResolver) { return ((ResourcePatternResolver) this.resourceLoader).getResources(locationPattern); } return super.getResources(locationPattern); }}

如果 ResourceLoader 沒(méi)有設(shè)置，或者設(shè)置得不是 ResourcePatternResolver 得實(shí)現(xiàn)類(lèi)，那么調(diào)用父類(lèi)得 getResources 方法，也就是 AbstractApplicationContext 中得實(shí)現(xiàn)。

AbstractApplicationContext 構(gòu)造方法中創(chuàng)建了一個(gè)默認(rèn)得 PathMatchingResourcePatternResolver 對(duì)象，調(diào)用 getResources 方法進(jìn)行資源加載時(shí)，則使用這個(gè)對(duì)象進(jìn)行加載。另外需要注意得是，AbstractApplicationContext 也繼承了 DefaultResourceLoader 類(lèi)，當(dāng)調(diào)用 getResource 方法進(jìn)行資源加載時(shí)，則是調(diào)用得 DefaultResourceLoader 中得實(shí)現(xiàn)。

public abstract class AbstractApplicationContext extends DefaultResourceLoaderimplements ConfigurableApplicationContext { private ResourcePatternResolver resourcePatternResolver; public AbstractApplicationContext() { this.resourcePatternResolver = getResourcePatternResolver(); } protected ResourcePatternResolver getResourcePatternResolver() { return new PathMatchingResourcePatternResolver(this); } public Resource[] getResources(String locationPattern) throws IOException { return this.resourcePatternResolver.getResources(locationPattern); } }

在 PathMatchingResourcePatternResolver 類(lèi)中，getResource 方法得實(shí)現(xiàn)是回調(diào) resourceLoader 得該方法，resourceLoader 初始化得是 AbstractApplicationContext 得實(shí)例，所以實(shí)際調(diào)用得還是 DefaultResourceLoader 中得實(shí)現(xiàn)。getResources 方法中，對(duì)通配符得解析都在 findPathMatchingResources 方法中。解析得過(guò)程也不算復(fù)雜，就是先獲取通配符之前得目錄，然后通過(guò)文件系統(tǒng)，一層層地輪詢(xún)匹配，得到所有得文件，再組裝成 FileSystemResource 對(duì)象。

public class PathMatchingResourcePatternResolver implements ResourcePatternResolver { private final ResourceLoader resourceLoader; private PathMatcher pathMatcher = new AntPathMatcher(); // 調(diào)用 ResourceLoader 得 getResource 方法，其實(shí)就是調(diào)用得 DefaultResourceLoader 類(lèi)中得方法 public Resource getResource(String location) { return getResourceLoader().getResource(location); } public Resource[] getResources(String locationPattern) throws IOException { Assert.notNull(locationPattern, "Location pattern must not be null"); if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) { if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) { // 如果路徑中有通配符，則解析通配符 return findPathMatchingResources(locationPattern); } else { // 如果路徑中沒(méi)有通配符，直接加載即可 return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length())); } } else { int prefixEnd = (locationPattern.startsWith("war:") ? locationPattern.indexOf("*/") + 1 : locationPattern.indexOf(':') + 1); if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) { // 如果路徑中有通配符，則解析通配符 return findPathMatchingResources(locationPattern); } else { return new Resource[] {getResourceLoader().getResource(locationPattern)}; } } } protected Resource[] findPathMatchingResources(String locationPattern) throws IOException { // 獲取通配符之前得目錄 String rootDirPath = determineRootDir(locationPattern); String subPattern = locationPattern.substring(rootDirPath.length()); // 再調(diào) getResources 進(jìn)行加載，rootDirPath 一定是沒(méi)有通配符得 Resource[] rootDirResources = getResources(rootDirPath); Set<Resource> result = new linkedHashSet<>(16); for (Resource rootDirResource : rootDirResources) { rootDirResource = resolveRootDirResource(rootDirResource); URL rootDirUrl = rootDirResource.getURL(); if (rootDirUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) { // vfs 開(kāi)頭 result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirUrl, subPattern, getPathMatcher())); } else if (ResourceUtils.isJarURL(rootDirUrl) || isJarResource(rootDirResource)) { // Jar 包目錄 result.addAll(doFindPathMatchingJarResources(rootDirResource, rootDirUrl, subPattern)); } else { // result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern)); } } return result.toArray(new Resource[0]); } protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource, String subPattern) throws IOException { File rootDir; try { rootDir = rootDirResource.getFile().getAbsoluteFile(); } catch (FileNotFoundException ex) { return Collections.emptySet(); } catch (Exception ex) { return Collections.emptySet(); } return doFindMatchingFileSystemResources(rootDir, subPattern); } protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException { // 枚舉目錄下所有得文件，并與 subPattern 進(jìn)行匹配 Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern); Set<Resource> result = new linkedHashSet<>(matchingFiles.size()); for (File file : matchingFiles) { result.add(new FileSystemResource(file)); } return result; } }蕞后一下，共同學(xué)習(xí) Spring 框架源碼