src/main/java/org/junit/rules/TemporaryFolder.java

package org.junit.rules;

import java.io.File;
import java.io.IOException;

import org.junit.Rule;

/**
 * The TemporaryFolder Rule allows creation of files and folders that should
 * be deleted when the test method finishes (whether it passes or
 * fails). Whether the deletion is successful or not is not checked by this rule.
 * No exception will be thrown in case the deletion fails.
 *
 * <p>Example of usage:
 * <pre>
 * public static class HasTempFolder {
 *  &#064;Rule
 *  public TemporaryFolder folder= new TemporaryFolder();
 *
 *  &#064;Test
 *  public void testUsingTempFolder() throws IOException {
 *      File createdFile= folder.newFile(&quot;myfile.txt&quot;);
 *      File createdFolder= folder.newFolder(&quot;subfolder&quot;);
 *      // ...
 *     }
 * }
 * </pre>
 *
 * @since 4.7
 */
public class TemporaryFolder extends ExternalResource {
    private final File parentFolder;
    private File folder;

    public TemporaryFolder() {
        this(null);
    }

    public TemporaryFolder(File parentFolder) {
        this.parentFolder = parentFolder;
    }

    @Override
    protected void before() throws Throwable {
        create();
    }

    @Override
    protected void after() {
        delete();
    }

    // testing purposes only

    /**
     * for testing purposes only. Do not use.
     */
    public void create() throws IOException {
        folder = createTemporaryFolderIn(parentFolder);
    }

    /**
     * Returns a new fresh file with the given name under the temporary folder.
     */
    public File newFile(String fileName) throws IOException {
        File file = new File(getRoot(), fileName);
        if (!file.createNewFile()) {
            throw new IOException(
                    "a file with the name \'" + fileName + "\' already exists in the test folder");
        }
        return file;
    }

    /**
     * Returns a new fresh file with a random name under the temporary folder.
     */
    public File newFile() throws IOException {
        return File.createTempFile("junit", null, getRoot());
    }

    /**
     * Returns a new fresh folder with the given name under the temporary
     * folder.
     */
    public File newFolder(String folder) throws IOException {
        return newFolder(new String[]{folder});
    }

    /**
     * Returns a new fresh folder with the given name(s) under the temporary
     * folder.
     */
    public File newFolder(String... folderNames) throws IOException {
        File file = getRoot();
        for (int i = 0; i < folderNames.length; i++) {
            String folderName = folderNames[i];
            validateFolderName(folderName);
            file = new File(file, folderName);
            if (!file.mkdir() && isLastElementInArray(i, folderNames)) {
                throw new IOException(
                        "a folder with the name \'" + folderName + "\' already exists");
            }
        }
        return file;
    }
    
    /**
     * Validates if multiple path components were used while creating a folder.
     * 
     * @param folderName
     *            Name of the folder being created
     */
    private void validateFolderName(String folderName) throws IOException {
        File tempFile = new File(folderName);
        if (tempFile.getParent() != null) {
            String errorMsg = "Folder name cannot consist of multiple path components separated by a file separator."
                    + " Please use newFolder('MyParentFolder','MyFolder') to create hierarchies of folders";
            throw new IOException(errorMsg);
        }
    }

    private boolean isLastElementInArray(int index, String[] array) {
        return index == array.length - 1;
    }

    /**
     * Returns a new fresh folder with a random name under the temporary folder.
     */
    public File newFolder() throws IOException {
        return createTemporaryFolderIn(getRoot());
    }

    private File createTemporaryFolderIn(File parentFolder) throws IOException {
        File createdFolder = File.createTempFile("junit", "", parentFolder);
        createdFolder.delete();
        createdFolder.mkdir();
        return createdFolder;
    }

    /**
     * @return the location of this temporary folder.
     */
    public File getRoot() {
        if (folder == null) {
            throw new IllegalStateException(
                    "the temporary folder has not yet been created");
        }
        return folder;
    }

    /**
     * Delete all files and folders under the temporary folder. Usually not
     * called directly, since it is automatically applied by the {@link Rule}
     */
    public void delete() {
        if (folder != null) {
            recursiveDelete(folder);
        }
    }

    private void recursiveDelete(File file) {
        File[] files = file.listFiles();
        if (files != null) {
            for (File each : files) {
                recursiveDelete(each);
            }
        }
        file.delete();
    }
}