springboot中关于classpath:路径使用及说明

2022-11-13 17:11:13 classpath 路径 springboot

1. 案例说明

在 resources下有model.conf文件，在配置文件中使用classpath:做为文件路径

1.1 解决方案

1.1.1 使用ResourcePatternResolver实现

使用classpath:做为路径

通过@value获取配置文件中的路径，后经过ResourcePatternResolver 获取文件

ResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        Resource resource = resolver.getResource("classpath:model.conf");
        String path = resource.getFile().getCanonicalPath();

1.1.2 使用 ClassPathResource实现

 ClassPathResource resource = new ClassPathResource("model.conf");
        String path = resource.getFile().getCanonicalPath();

ClassPathResource使用时，文件路径中不存在classpath:

1.1.3 使用Spring框架中ResourceUtils实现

File file = ResourceUtils.getFile("classpath:model.conf");
String path = file.getCanonicalPath();

2. ResourceUtils使用说明

2.1 源码展示


public abstract class ResourceUtils {
	
	public static final String CLASSPATH_URL_PREFIX = "classpath:";
	
	public static final String FILE_URL_PREFIX = "file:";
	
	public static final String JAR_URL_PREFIX = "jar:";
	
	public static final String WAR_URL_PREFIX = "war:";
	
	public static final String URL_PROTOCOL_FILE = "file";
	
	public static final String URL_PROTOCOL_JAR = "jar";
	
	public static final String URL_PROTOCOL_WAR = "war";
	
	public static final String URL_PROTOCOL_ZIP = "zip";
	
	public static final String URL_PROTOCOL_WSJAR = "wsjar";
	
	public static final String URL_PROTOCOL_VFSZIP = "vfszip";
	
	public static final String URL_PROTOCOL_VFSFILE = "vfsfile";
	
	public static final String URL_PROTOCOL_VFS = "vfs";
	
	public static final String JAR_FILE_EXTENSioN = ".jar";
	
	public static final String JAR_URL_SEPARATOR = "!/";
	
	public static final String WAR_URL_SEPARATOR = "*/";
	
	public static boolean isUrl(@Nullable String resourceLocation) {
		if (resourceLocation == null) {
			return false;
		}
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			return true;
		}
		try {
			new URL(resourceLocation);
			return true;
		}
		catch (MalfORMedURLException ex) {
			return false;
		}
	}
	
	public static URL getURL(String resourceLocation) throws FileNotFoundException {
		Assert.notNull(resourceLocation, "Resource location must not be null");
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
			ClassLoader cl = ClassUtils.getDefaultClassLoader();
			URL url = (cl != null ? cl.getResource(path) : ClassLoader.getSystemResource(path));
			if (url == null) {
				String description = "class path resource [" + path + "]";
				throw new FileNotFoundException(description +
						" cannot be resolved to URL because it does not exist");
			}
			return url;
		}
		try {
			// try URL
			return new URL(resourceLocation);
		}
		catch (MalformedURLException ex) {
			// no URL -> treat as file path
			try {
				return new File(resourceLocation).toURI().toURL();
			}
			catch (MalformedURLException ex2) {
				throw new FileNotFoundException("Resource location [" + resourceLocation +
						"] is neither a URL not a well-formed file path");
			}
		}
	}
	
	public static File getFile(String resourceLocation) throws FileNotFoundException {
		Assert.notNull(resourceLocation, "Resource location must not be null");
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
			String description = "class path resource [" + path + "]";
			ClassLoader cl = ClassUtils.getDefaultClassLoader();
			URL url = (cl != null ? cl.getResource(path) : ClassLoader.getSystemResource(path));
			if (url == null) {
				throw new FileNotFoundException(description +
						" cannot be resolved to absolute file path because it does not exist");
			}
			return getFile(url, description);
		}
		try {
			// try URL
			return getFile(new URL(resourceLocation));
		}
		catch (MalformedURLException ex) {
			// no URL -> treat as file path
			return new File(resourceLocation);
		}
	}
	
	public static File getFile(URL resourceUrl) throws FileNotFoundException {
		return getFile(resourceUrl, "URL");
	}
	
	public static File getFile(URL resourceUrl, String description) throws FileNotFoundException {
		Assert.notNull(resourceUrl, "Resource URL must not be null");
		if (!URL_PROTOCOL_FILE.equals(resourceUrl.getProtocol())) {
			throw new FileNotFoundException(
					description + " cannot be resolved to absolute file path " +
					"because it does not reside in the file system: " + resourceUrl);
		}
		try {
			return new File(toURI(resourceUrl).getSchemeSpecificPart());
		}
		catch (URISyntaxException ex) {
			// Fallback for URLs that are not valid URIs (should hardly ever happen).
			return new File(resourceUrl.getFile());
		}
	}
	
	public static File getFile(URI resourceUri) throws FileNotFoundException {
		return getFile(resourceUri, "URI");
	}
	
	public static File getFile(URI resourceUri, String description) throws FileNotFoundException {
		Assert.notNull(resourceUri, "Resource URI must not be null");
		if (!URL_PROTOCOL_FILE.equals(resourceUri.getScheme())) {
			throw new FileNotFoundException(
					description + " cannot be resolved to absolute file path " +
					"because it does not reside in the file system: " + resourceUri);
		}
		return new File(resourceUri.getSchemeSpecificPart());
	}
	
	public static boolean isFileURL(URL url) {
		String protocol = url.getProtocol();
		return (URL_PROTOCOL_FILE.equals(protocol) || URL_PROTOCOL_VFSFILE.equals(protocol) ||
				URL_PROTOCOL_VFS.equals(protocol));
	}
	
	public static boolean isJarURL(URL url) {
		String protocol = url.getProtocol();
		return (URL_PROTOCOL_JAR.equals(protocol) || URL_PROTOCOL_WAR.equals(protocol) ||
				URL_PROTOCOL_ZIP.equals(protocol) || URL_PROTOCOL_VFSZIP.equals(protocol) ||
				URL_PROTOCOL_WSJAR.equals(protocol));
	}
	
	public static boolean isJarFileURL(URL url) {
		return (URL_PROTOCOL_FILE.equals(url.getProtocol()) &&
				url.getPath().toLowerCase().endsWith(JAR_FILE_EXTENSION));
	}
	
	public static URL extractJarFileURL(URL jarUrl) throws MalformedURLException {
		String urlFile = jarUrl.getFile();
		int separatorIndex = urlFile.indexOf(JAR_URL_SEPARATOR);
		if (separatorIndex != -1) {
			String jarFile = urlFile.substring(0, separatorIndex);
			try {
				return new URL(jarFile);
			}
			catch (MalformedURLException ex) {
				// Probably no protocol in original jar URL, like "jar:C:/mypath/myjar.jar".
				// This usually indicates that the jar file resides in the file system.
				if (!jarFile.startsWith("/")) {
					jarFile = "/" + jarFile;
				}
				return new URL(FILE_URL_PREFIX + jarFile);
			}
		}
		else {
			return jarUrl;
		}
	}
	
	public static URL extractArcHiveURL(URL jarUrl) throws MalformedURLException {
		String urlFile = jarUrl.getFile();
		int endIndex = urlFile.indexOf(WAR_URL_SEPARATOR);
		if (endIndex != -1) {
			// Tomcat's "war:file:...mywar.war*/WEB-INF/lib/myjar.jar!/myentry.txt"
			String warFile = urlFile.substring(0, endIndex);
			if (URL_PROTOCOL_WAR.equals(jarUrl.getProtocol())) {
				return new URL(warFile);
			}
			int startIndex = warFile.indexOf(WAR_URL_PREFIX);
			if (startIndex != -1) {
				return new URL(warFile.substring(startIndex + WAR_URL_PREFIX.length()));
			}
		}
		// Regular "jar:file:...myjar.jar!/myentry.txt"
		return extractJarFileURL(jarUrl);
	}
	
	public static URI toURI(URL url) throws URISyntaxException {
		return toURI(url.toString());
	}
	
	public static URI toURI(String location) throws URISyntaxException {
		return new URI(StringUtils.replace(location, " ", "%20"));
	}
	
	public static void useCachesIfNecessary(URLConnection con) {
		con.setUseCaches(con.getClass().getSimpleName().startsWith("JNLP"));
	}
}

2.2 常用方法

2.2.1 extractJarFileURL

public static URL extractJarFileURL(URL jarUrl)

从给定的URL (URL可以指向jar文件中的资源或jar文件本身)中提取实际jar文件的URL

2.2.2 getFile

getFile(String resourceLocation)：将给定的资源位置解析为java.io.file
getFile(URI resourceUri) ：将给定的资源位置解析为java.io.file
getFile(String resourceLocation) ：将给定的资源位置解析为java.io.file
getFile(URL resourceUrl, String description) ：将给定的资源位置解析为java.io.file
getFile(URL resourceUrl, String description) ：将给定的资源位置解析为java.io.file

2.2.3 getURL

getURL(String resourceLocation)

将给定的资源位置解析为java.net.URL

2.2.4 isJarURL

isJarURL(URL url)

确定给定的URL是否指向jar文件中的资源，即具有协议“jar”、“zip”、“wsjar”或“代码源”

2.2.5 isUrl

返回给定资源位置是否是URL:一个特殊的“classpath”伪URL还是一个标准URL。

2.2.6 toURI

toURI(String location) ：为给定的URL创建一个URI实例，首先用“%20”引号替换空格。
toURI(URL url) ：为给定的URL创建一个URI实例，首先用“%20”引号替换空格。

3. 常见问题

3.1 打成jar后获取不到文件

Resource下的文件是存在于jar这个文件里面，在磁盘上是没有真实路径存在的，它是位于jar内部的一个路径。所以通过ResourceUtils.getFile或者this.getClass().getResource("")方法无法正确获取文件。

解决方案：

BufferedReader in = new BufferedReader(new InputStreamReader(this.getClass().getClassLoader().getResourceAsStream(path)));
StringBuffer buffer = new StringBuffer();
String line = "";
while ((line = in.readLine()) != null){
    buffer.append(line);
}
String input = buffer.toString();

以上为个人经验，希望能给大家一个参考，也希望大家多多支持。

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