File to URI:     

File file = ...;           URI uri = file.toURI();

File to URL:     

File file = ...;           URL url = file.toURI().URL();

URL to File:     

URL url = ...;           File file = new Path(url.getPath()).toFile();

URI to URL:     

URI uri = ...;           URL url = uri.toURL();

URL to URI:     

URL url = ...;           URI uri = url.toURI();

一般情况下采用上述方式都可以安全的使用.

但是, 当处理本地路径且有空格,或者特殊字符,比如汉字等. 路径在相互的转换过程中, 可能会出现转换的无效字符错误异常.
所以, 可以使用Eclipse提供的工具类org.eclipse.core.runtime.URIUtil (插件: org.eclipse.equinox.simpleconfigurator)来进行转换.

比如URL to File:   

URL url = ...;           File file = URIUtil.toFile(URIUtil.toURI(url));

当URL, URI直接互相转换时,也可以使用该URIUtil工具类.

• toURI

• toURL

还有一个工具类,就是org.eclipse.core.runtime.FileLocator(插件: org.eclipse.equinox.common) 也可以对URL进行File的格式化. 比如toFileURL方法.


附源码:

package org.eclipse.equinox.internal.simpleconfigurator.utils; import java.io.File; import java.net.*; public class URIUtil {     private static final String SCHEME_FILE = "file"; //$NON-NLS-1$     private static final String UNC_PREFIX = "//"; //$NON-NLS-1$         public static URI append(URI base, String extension) {         try {             String path = base.getPath();             if (path == null)                 return appendOpaque(base, extension);             //if the base is already a directory then resolve will just do the right thing             if (path.endsWith("/")) {//$NON-NLS-1$                 URI result = base.resolve(extension);                 //Fix UNC paths that are incorrectly normalized by URI#resolve (see Java bug 4723726)                 String resultPath = result.getPath();                 if (path.startsWith(UNC_PREFIX) && (resultPath == null || !resultPath.startsWith(UNC_PREFIX)))                     result = new URI(result.getScheme(), "///" + result.getSchemeSpecificPart(), result.getFragment()); //$NON-NLS-1$                 return result;             }             path = path + "/" + extension; //$NON-NLS-1$             return new URI(base.getScheme(), base.getUserInfo(), base.getHost(), base.getPort(), path, base.getQuery(), base.getFragment());         } catch (URISyntaxException e) {             //shouldn't happen because we started from a valid URI             throw new RuntimeException(e);         }     }         private static URI appendOpaque(URI base, String extension) throws URISyntaxException {         String ssp = base.getSchemeSpecificPart();         if (ssp.endsWith("/")) //$NON-NLS-1$             ssp += extension;         else             ssp = ssp + "/" + extension; //$NON-NLS-1$         return new URI(base.getScheme(), ssp, base.getFragment());     }         public static URI fromString(String uriString) throws URISyntaxException {         int colon = uriString.indexOf(':');         int hash = uriString.lastIndexOf('#');         boolean noHash = hash < 0;         if (noHash)             hash = uriString.length();         String scheme = colon < 0 ? null : uriString.substring(0, colon);         String ssp = uriString.substring(colon + 1, hash);         String fragment = noHash ? null : uriString.substring(hash + 1);         //use java.io.File for constructing file: URIs         if (scheme != null && scheme.equals(SCHEME_FILE)) {             File file = new File(uriString.substring(5));             if (file.isAbsolute())                 return file.toURI();             scheme = null;             if (File.separatorChar != '/')                 ssp = ssp.replace(File.separatorChar, '/');         }         return new URI(scheme, ssp, fragment);     }         public static boolean sameURI(URI url1, URI url2) {         if (url1 == url2)             return true;         if (url1 == null || url2 == null)             return false;         if (url1.equals(url2))             return true;         if (url1.isAbsolute() != url2.isAbsolute())             return false;         // check if we have two local file references that are case variants         File file1 = toFile(url1);         return file1 == null ? false : file1.equals(toFile(url2));     }         public static File toFile(URI uri) {         try {             if (!SCHEME_FILE.equalsIgnoreCase(uri.getScheme()))                 return null;             //assume all illegal characters have been properly encoded, so use URI class to unencode             return new File(uri);         } catch (IllegalArgumentException e) {             //File constructor does not support non-hierarchical URI             String path = uri.getPath();             //path is null for non-hierarchical URI such as file:c:/tmp             if (path == null)                 path = uri.getSchemeSpecificPart();             return new File(path);         }     }         public static String toUnencodedString(URI uri) {         StringBuffer result = new StringBuffer();         String scheme = uri.getScheme();         if (scheme != null)             result.append(scheme).append(':');         //there is always a ssp         result.append(uri.getSchemeSpecificPart());         String fragment = uri.getFragment();         if (fragment != null)             result.append('#').append(fragment);         return result.toString();     }         public static URI toURI(URL url) throws URISyntaxException {         //URL behaves differently across platforms so for file: URLs we parse from string form         if (SCHEME_FILE.equals(url.getProtocol())) {             String pathString = url.toExternalForm().substring(5);             //ensure there is a leading slash to handle common malformed URLs such as file:c:/tmp             if (pathString.indexOf('/') != 0)                 pathString = '/' + pathString;             else if (pathString.startsWith(UNC_PREFIX) && !pathString.startsWith(UNC_PREFIX, 2)) {                 //URL encodes UNC path with two slashes, but URI uses four (see bug 207103)                 pathString = UNC_PREFIX + pathString;             }             return new URI(SCHEME_FILE, null, pathString, null);         }         try {             return new URI(url.toExternalForm());         } catch (URISyntaxException e) {             //try multi-argument URI constructor to perform encoding             return new URI(url.getProtocol(), url.getUserInfo(), url.getHost(), url.getPort(), url.getPath(), url.getQuery(), url.getRef());         }     }         public static URL toURL(URI uri) throws MalformedURLException {         return new URL(uri.toString());     } }