Add application specific temp folder support

Add ApplicationTemp class which can be used to obtain a temp folder
based on the running application. Allows restarted application to
find temp files saved in a previous run.

Fixes gh-3529

spring-boot/src/main/java/org/springframework/boot/ApplicationTemp.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2012-2015 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
+ *
+ *      http://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.boot;
+
+import java.io.File;
+import java.security.MessageDigest;
+
+import org.springframework.util.Assert;
+import org.springframework.util.StringUtils;
+
+/**
+ * Provides access to an application specific temporary folder. Generally speaking
+ * different Spring Boot applications will get different locations, however, simply
+ * restarting an application will give the same location.
+ *
+ * @author Phillip Webb
+ * @since 1.3.0
+ */
+public class ApplicationTemp {
+
+	private static final char[] HEX_CHARS = "0123456789ABCDEF".toCharArray();
+
+	private final Class<?> sourceClass;
+
+	private volatile File folder;
+
+	/**
+	 * Create a new {@link ApplicationTemp} instance.
+	 */
+	public ApplicationTemp() {
+		this(null);
+	}
+
+	/**
+	 * Create a new {@link ApplicationTemp} instance for the specified source class.
+	 * @param sourceClass the source class or {@code null}
+	 */
+	public ApplicationTemp(Class<?> sourceClass) {
+		this.sourceClass = sourceClass;
+	}
+
+	@Override
+	public String toString() {
+		return getFolder().getAbsolutePath();
+	}
+
+	/**
+	 * Return a subfolder of the application temp.
+	 * @param subFolder the subfolder name
+	 * @return a subfolder
+	 */
+	public File getFolder(String subFolder) {
+		File folder = new File(getFolder(), subFolder);
+		folder.mkdirs();
+		return folder;
+	}
+
+	/**
+	 * Return the folder to be used for application specific temp files.
+	 * @return the application temp folder
+	 */
+	public File getFolder() {
+		if (this.folder == null) {
+			synchronized (this) {
+				byte[] hash = generateHash(this.sourceClass);
+				this.folder = new File(getTempDirectory(), toHexString(hash));
+				this.folder.mkdirs();
+				Assert.state(this.folder.exists(), "Unable to create temp folder "
+						+ this.folder);
+			}
+		}
+		return this.folder;
+	}
+
+	private File getTempDirectory() {
+		String property = System.getProperty("java.io.tmpdir");
+		Assert.state(StringUtils.hasLength(property), "No 'java.io.tmpdir' property set");
+		File file = new File(property);
+		Assert.state(file.exists(), "Temp folder " + file + " does not exist");
+		Assert.state(file.isDirectory(), "Temp location " + file + " is not a folder");
+		return file;
+	}
+
+	private byte[] generateHash(Class<?> sourceClass) {
+		ApplicationHome home = new ApplicationHome(sourceClass);
+		MessageDigest digest;
+		try {
+			digest = MessageDigest.getInstance("SHA-1");
+			update(digest, home.getSource());
+			update(digest, home.getDir());
+			update(digest, System.getProperty("user.dir"));
+			update(digest, System.getProperty("java.home"));
+			update(digest, System.getProperty("java.class.path"));
+			update(digest, System.getProperty("sun.java.command"));
+			update(digest, System.getProperty("sun.boot.class.path"));
+			return digest.digest();
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
+	private void update(MessageDigest digest, Object source) {
+		if (source != null) {
+			digest.update(getUpdateSourceBytes(source));
+		}
+	}
+
+	private byte[] getUpdateSourceBytes(Object source) {
+		if (source instanceof File) {
+			return getUpdateSourceBytes(((File) source).getAbsolutePath());
+		}
+		return source.toString().getBytes();
+	}
+
+	private String toHexString(byte[] bytes) {
+		char[] hex = new char[bytes.length * 2];
+		for (int i = 0; i < bytes.length; i++) {
+			int b = bytes[i] & 0xFF;
+			hex[i * 2] = HEX_CHARS[b >>> 4];
+			hex[i * 2 + 1] = HEX_CHARS[b & 0x0F];
+		}
+		return new String(hex);
+	}
+
+}

spring-boot/src/test/java/org/springframework/boot/ApplicationTempTests.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2012-2015 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
+ *
+ *      http://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.boot;
+
+import java.io.File;
+
+import org.junit.Test;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Tests for {@link ApplicationTemp}.
+ *
+ * @author Phillip Webb
+ */
+public class ApplicationTempTests {
+
+	@Test
+	public void generatesConsistentTemp() throws Exception {
+		ApplicationTemp t1 = new ApplicationTemp();
+		ApplicationTemp t2 = new ApplicationTemp();
+		assertThat(t1.getFolder(), notNullValue());
+		assertThat(t1.getFolder(), equalTo(t2.getFolder()));
+	}
+
+	@Test
+	public void differentBasedOnUserDir() throws Exception {
+		String userDir = System.getProperty("user.dir");
+		try {
+			File t1 = new ApplicationTemp().getFolder();
+			System.setProperty("user.dir", "abc");
+			File t2 = new ApplicationTemp().getFolder();
+			assertThat(t1, not(equalTo(t2)));
+		}
+		finally {
+			System.setProperty("user.dir", userDir);
+		}
+	}
+
+	@Test
+	public void getSubFolder() throws Exception {
+		ApplicationTemp temp = new ApplicationTemp();
+		assertThat(temp.getFolder("abc"), equalTo(new File(temp.getFolder(), "abc")));
+	}
+
+}