Add enumeration of supported Resource prefixes (e.g. classpath:).

Additionally, the enum defines operations on the Resource prefixes for convenience.

Resolves gh-92.

spring-geode/src/main/java/org/springframework/geode/core/io/support/ResourcePrefix.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package org.springframework.geode.core.io.support;
+
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * An enumeration of {@link Resource} {@link String prefixes} recognized by the Spring Framework.
+ *
+ * @author John Blum
+ * @see org.springframework.core.io.Resource
+ * @since 1.3.1
+ */
+public enum ResourcePrefix {
+
+	CLASSPATH_URL_PREFIX(ResourceLoader.CLASSPATH_URL_PREFIX),
+	FILESYSTEM_URL_PREFIX("file:"),
+	HTTP_URL_PREFIX("http:");
+
+	public static final String RESOURCE_PATH_SEPARATOR = "/";
+
+	/**
+	 * Factory method used to try and find a {@link ResourcePrefix} enumerated value
+	 * matching the given {@link String prefix}.
+	 *
+	 * @param prefix {@link String} with the name of the prefix.
+	 * @return a {@link ResourcePrefix} matching the given {@link String prefix} by name, or {@literal null}
+	 * if the {@link String prefix} does not match any {@link ResourcePrefix} enumerated value.
+	 */
+	public static @Nullable ResourcePrefix from(@Nullable String prefix) {
+
+		if (StringUtils.hasText(prefix)) {
+
+			prefix = prefix.trim().toLowerCase();
+
+			for (ResourcePrefix resourcePrefix : values()) {
+				if (resourcePrefix.toString().equals(prefix)) {
+					return resourcePrefix;
+				}
+			}
+		}
+
+		return null;
+	}
+
+	private final String prefix;
+
+	/**
+	 * Constructs a new instance of {@link ResourcePrefix} initialized with the named {@link String prefix}.
+	 *
+	 * @param prefix {@link String name} of the prefix.
+	 * @throws IllegalArgumentException if the {@link String prefix} is not specified.
+	 */
+	ResourcePrefix(String prefix) {
+		Assert.hasText(prefix, "Resource prefix must be specified");
+		this.prefix = prefix;
+	}
+
+	/**
+	 * Gets the network protocol that this {@link ResourcePrefix} represents.
+	 *
+	 * @return the network protocol that this {@link ResourcePrefix} represents.
+	 */
+	public String getProtocol() {
+
+		StringBuilder buffer = new StringBuilder();
+
+		for (char character : this.prefix.toCharArray()) {
+			if (Character.isAlphabetic(character)) {
+				buffer.append(character);
+			}
+		}
+
+		return buffer.toString();
+	}
+
+	/**
+	 * Gets the {@link String pattern} or template used to construct a {@link java.net.URL} prefix
+	 * from this {@link ResourcePrefix}.
+	 *
+	 * @return the {@link String pattern} or template used to construct a {@link java.net.URL} prefix
+	 * from this {@link ResourcePrefix}.
+	 * @see #toUrlPrefix()
+	 */
+	protected String getUrlPrefixPattern() {
+		return this.equals(CLASSPATH_URL_PREFIX) ? "%s" : "%1$s%2$s%2$s";
+	}
+
+	@Override
+	public String toString() {
+		return this.prefix;
+	}
+
+	/**
+	 * Gets the {@link ResourcePrefix} as a prefix use in a {@link java.net.URL}.
+	 *
+	 * @return the {@link java.net.URL} prefix.
+	 * @see #getUrlPrefixPattern()
+	 */
+	public String toUrlPrefix() {
+		return String.format(getUrlPrefixPattern(), toString(), RESOURCE_PATH_SEPARATOR);
+	}
+}

spring-geode/src/test/java/org/springframework/geode/core/io/support/ResourcePrefixUnitTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package org.springframework.geode.core.io.support;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+import org.springframework.core.io.ResourceLoader;
+
+/**
+ * Unit Tests for {@link ResourcePrefix}.
+ *
+ * @author John Blum
+ * @see org.junit.Test
+ * @since 1.3.1
+ */
+public class ResourcePrefixUnitTests {
+
+	@Test
+	public void fromReturnsResourcePrefix() {
+
+		assertThat(ResourcePrefix.from(ResourceLoader.CLASSPATH_URL_PREFIX))
+			.isEqualTo(ResourcePrefix.CLASSPATH_URL_PREFIX);
+
+		for (ResourcePrefix prefix : ResourcePrefix.values()) {
+			assertThat(ResourcePrefix.from(prefix.toString())).isEqualTo(prefix);
+		}
+	}
+
+	@Test
+	public void fromInvalidPrefixReturnsNull() {
+
+		assertThat(ResourcePrefix.from("ftp:")).isNull();
+		assertThat(ResourcePrefix.from("scp:")).isNull();
+		assertThat(ResourcePrefix.from("smtp:")).isNull();
+		assertThat(ResourcePrefix.from("  ")).isNull();
+		assertThat(ResourcePrefix.from("")).isNull();
+		assertThat(ResourcePrefix.from(null)).isNull();
+	}
+
+	@Test
+	public void getProtocolIsCorrect() {
+
+		assertThat(ResourcePrefix.CLASSPATH_URL_PREFIX.getProtocol()).isEqualTo("classpath");
+		assertThat(ResourcePrefix.FILESYSTEM_URL_PREFIX.getProtocol()).isEqualTo("file");
+		assertThat(ResourcePrefix.HTTP_URL_PREFIX.getProtocol()).isEqualTo("http");
+	}
+
+	@Test
+	public void toUrlPrefix() {
+
+		assertThat(ResourcePrefix.CLASSPATH_URL_PREFIX.toUrlPrefix()).isEqualTo("classpath:");
+		assertThat(ResourcePrefix.FILESYSTEM_URL_PREFIX.toUrlPrefix()).isEqualTo("file://");
+		assertThat(ResourcePrefix.HTTP_URL_PREFIX.toUrlPrefix()).isEqualTo("http://");
+	}
+}