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springboot中关于classpath:路径使用及说明

来源：互联网收集：自由互联发布时间：2023-01-30

目录 1. 案例说明 1.1 解决方案 2. ResourceUtils使用说明 2.1 源码展示 2.2 常用方法 3. 常见问题 3.1 打成jar后获取不到文件 1. 案例说明在 resources下有model.conf文件，在配置文件中使用classpat

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

/**
 * Utility methods for resolving resource locations to files in the
 * file system. Mainly for internal use within the framework.
 *
 * <p>Consider using Spring's Resource abstraction in the core package
 * for handling all kinds of file resources in a uniform manner.
 * {@link org.springframework.core.io.ResourceLoader}'s {@code getResource()}
 * method can resolve any location to a {@link org.springframework.core.io.Resource}
 * object, which in turn allows one to obtain a {@code java.io.File} in the
 * file system through its {@code getFile()} method.
 *
 * @author Juergen Hoeller
 * @since 1.1.5
 * @see org.springframework.core.io.Resource
 * @see org.springframework.core.io.ClassPathResource
 * @see org.springframework.core.io.FileSystemResource
 * @see org.springframework.core.io.UrlResource
 * @see org.springframework.core.io.ResourceLoader
 */
public abstract class ResourceUtils {
	/** Pseudo URL prefix for loading from the class path: "classpath:" */
	public static final String CLASSPATH_URL_PREFIX = "classpath:";
	/** URL prefix for loading from the file system: "file:" */
	public static final String FILE_URL_PREFIX = "file:";
	/** URL prefix for loading from a jar file: "jar:" */
	public static final String JAR_URL_PREFIX = "jar:";
	/** URL prefix for loading from a war file on Tomcat: "war:" */
	public static final String WAR_URL_PREFIX = "war:";
	/** URL protocol for a file in the file system: "file" */
	public static final String URL_PROTOCOL_FILE = "file";
	/** URL protocol for an entry from a jar file: "jar" */
	public static final String URL_PROTOCOL_JAR = "jar";
	/** URL protocol for an entry from a war file: "war" */
	public static final String URL_PROTOCOL_WAR = "war";
	/** URL protocol for an entry from a zip file: "zip" */
	public static final String URL_PROTOCOL_ZIP = "zip";
	/** URL protocol for an entry from a WebSphere jar file: "wsjar" */
	public static final String URL_PROTOCOL_WSJAR = "wsjar";
	/** URL protocol for an entry from a JBoss jar file: "vfszip" */
	public static final String URL_PROTOCOL_VFSZIP = "vfszip";
	/** URL protocol for a JBoss file system resource: "vfsfile" */
	public static final String URL_PROTOCOL_VFSFILE = "vfsfile";
	/** URL protocol for a general JBoss VFS resource: "vfs" */
	public static final String URL_PROTOCOL_VFS = "vfs";
	/** File extension for a regular jar file: ".jar" */
	public static final String JAR_FILE_EXTENSION = ".jar";
	/** Separator between JAR URL and file path within the JAR: "!/" */
	public static final String JAR_URL_SEPARATOR = "!/";
	/** Special separator between WAR URL and jar part on Tomcat */
	public static final String WAR_URL_SEPARATOR = "*/";
	/**
	 * Return whether the given resource location is a URL:
	 * either a special "classpath" pseudo URL or a standard URL.
	 * @param resourceLocation the location String to check
	 * @return whether the location qualifies as a URL
	 * @see #CLASSPATH_URL_PREFIX
	 * @see java.net.URL
	 */
	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;
		}
	}
	/**
	 * Resolve the given resource location to a {@code java.net.URL}.
	 * <p>Does not check whether the URL actually exists; simply returns
	 * the URL that the given location would correspond to.
	 * @param resourceLocation the resource location to resolve: either a
	 * "classpath:" pseudo URL, a "file:" URL, or a plain file path
	 * @return a corresponding URL object
	 * @throws FileNotFoundException if the resource cannot be resolved to a URL
	 */
	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");
			}
		}
	}
	/**
	 * Resolve the given resource location to a {@code java.io.File},
	 * i.e. to a file in the file system.
	 * <p>Does not check whether the file actually exists; simply returns
	 * the File that the given location would correspond to.
	 * @param resourceLocation the resource location to resolve: either a
	 * "classpath:" pseudo URL, a "file:" URL, or a plain file path
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the resource cannot be resolved to
	 * a file in the file system
	 */
	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);
		}
	}
	/**
	 * Resolve the given resource URL to a {@code java.io.File},
	 * i.e. to a file in the file system.
	 * @param resourceUrl the resource URL to resolve
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 */
	public static File getFile(URL resourceUrl) throws FileNotFoundException {
		return getFile(resourceUrl, "URL");
	}
	/**
	 * Resolve the given resource URL to a {@code java.io.File},
	 * i.e. to a file in the file system.
	 * @param resourceUrl the resource URL to resolve
	 * @param description a description of the original resource that
	 * the URL was created for (for example, a class path location)
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 */
	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());
		}
	}
	/**
	 * Resolve the given resource URI to a {@code java.io.File},
	 * i.e. to a file in the file system.
	 * @param resourceUri the resource URI to resolve
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 * @since 2.5
	 */
	public static File getFile(URI resourceUri) throws FileNotFoundException {
		return getFile(resourceUri, "URI");
	}
	/**
	 * Resolve the given resource URI to a {@code java.io.File},
	 * i.e. to a file in the file system.
	 * @param resourceUri the resource URI to resolve
	 * @param description a description of the original resource that
	 * the URI was created for (for example, a class path location)
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 * @since 2.5
	 */
	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());
	}
	/**
	 * Determine whether the given URL points to a resource in the file system,
	 * i.e. has protocol "file", "vfsfile" or "vfs".
	 * @param url the URL to check
	 * @return whether the URL has been identified as a file system URL
	 */
	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));
	}
	/**
	 * Determine whether the given URL points to a resource in a jar file.
	 * i.e. has protocol "jar", "war, ""zip", "vfszip" or "wsjar".
	 * @param url the URL to check
	 * @return whether the URL has been identified as a JAR URL
	 */
	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));
	}
	/**
	 * Determine whether the given URL points to a jar file itself,
	 * that is, has protocol "file" and ends with the ".jar" extension.
	 * @param url the URL to check
	 * @return whether the URL has been identified as a JAR file URL
	 * @since 4.1
	 */
	public static boolean isJarFileURL(URL url) {
		return (URL_PROTOCOL_FILE.equals(url.getProtocol()) &&
				url.getPath().toLowerCase().endsWith(JAR_FILE_EXTENSION));
	}
	/**
	 * Extract the URL for the actual jar file from the given URL
	 * (which may point to a resource in a jar file or to a jar file itself).
	 * @param jarUrl the original URL
	 * @return the URL for the actual jar file
	 * @throws MalformedURLException if no valid jar file URL could be extracted
	 */
	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;
		}
	}
	/**
	 * Extract the URL for the outermost archive from the given jar/war URL
	 * (which may point to a resource in a jar file or to a jar file itself).
	 * <p>In the case of a jar file nested within a war file, this will return
	 * a URL to the war file since that is the one resolvable in the file system.
	 * @param jarUrl the original URL
	 * @return the URL for the actual jar file
	 * @throws MalformedURLException if no valid jar file URL could be extracted
	 * @since 4.1.8
	 * @see #extractJarFileURL(URL)
	 */
	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);
	}
	/**
	 * Create a URI instance for the given URL,
	 * replacing spaces with "%20" URI encoding first.
	 * @param url the URL to convert into a URI instance
	 * @return the URI instance
	 * @throws URISyntaxException if the URL wasn't a valid URI
	 * @see java.net.URL#toURI()
	 */
	public static URI toURI(URL url) throws URISyntaxException {
		return toURI(url.toString());
	}
	/**
	 * Create a URI instance for the given location String,
	 * replacing spaces with "%20" URI encoding first.
	 * @param location the location String to convert into a URI instance
	 * @return the URI instance
	 * @throws URISyntaxException if the location wasn't a valid URI
	 */
	public static URI toURI(String location) throws URISyntaxException {
		return new URI(StringUtils.replace(location, " ", "%20"));
	}
	/**
	 * Set the {@link URLConnection#setUseCaches "useCaches"} flag on the
	 * given connection, preferring {@code false} but leaving the
	 * flag at {@code true} for JNLP based resources.
	 * @param con the URLConnection to set the flag on
	 */
	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自由互联。

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