本文主要探讨了Apache Commons-IO中的FileUtils类，重点讲解了如何比较文件、使用InputStreamReader处理文件编码以及文件复制和删除的细节。通过学习，可以提升对JAVA IO的理解和操作能力。
由于Android项目忙完，苦于学习方向迷失，决定开一个进度，学习解析commons-IO包，提高JAVA水平，学习JAVA IO部分。
废话不多说，进入正题。
1.
//-----------------------------------------------------------------------
/**
* Compares the contents of two files to determine if they are equal or not.
* <p>
* This method checks to see if the two files are different lengths
* or if they point to the same file, before resorting to byte-by-byte
* comparison of the contents.
* <p>
* Code origin: Avalon
*
* @param file1 the first file
* @param file2 the second file
* @return true if the content of the files are equal or they both don't
* exist, false otherwise
* @throws IOException in case of an I/O error
*/
public static boolean contentEquals(File file1, File file2) throws IOException {
boolean file1Exists = file1.exists();
if (file1Exists != file2.exists()) {
return false;
}
if (!file1Exists) {
// two not existing files are equal
return true;
}
if (file1.isDirectory() || file2.isDirectory()) {
// don't want to compare directory contents
throw new IOException("Can't compare directories, only files");
}
if (file1.length() != file2.length()) {
// lengths differ, cannot be equal
return false;
}
if (file1.getCanonicalFile().equals(file2.getCanonicalFile())) {
// same file
return true;
}
InputStream input1 = null;
InputStream input2 = null;
try {
input1 = new FileInputStream(file1);
input2 = new FileInputStream(file2);
return IOUtils.contentEquals(input1, input2);
} finally {
IOUtils.closeQuietly(input1);
IOUtils.closeQuietly(input2);
}
}比较策略：
1.判断是否有一个存在一个不存在（两个不存在也算相同）
2.判断两个是不是至少一个是目录（不能比较目录内容）
3.判断两个文件的长度是否相同，不同则返回false
4.应用File.getCanonicalFile()这个函数返回文件路径判断是不是指向同一个文件
5.最后才用inputstream导入两个文件，使用IOUtils.contentEquals(input1, input2)判断内容是否相等
2.
/**
* Compares the contents of two files to determine if they are equal or not.
* <p>
* This method checks to see if the two files point to the same file,
* before resorting to line-by-line comparison of the contents.
* <p>
*
* @param file1 the first file
* @param file2 the second file
* @param charsetName the character encoding to be used.
* May be null, in which case the platform default is used
* @return true if the content of the files are equal or neither exists,
* false otherwise
* @throws IOException in case of an I/O error
* @since 2.2
* @see IOUtils#contentEqualsIgnoreEOL(Reader, Reader)
*/
public static boolean contentEqualsIgnoreEOL(File file1, File file2, String charsetName) throws IOException {
boolean file1Exists = file1.exists();
if (file1Exists != file2.exists()) {
return false;
}
if (!file1Exists) {
// two not existing files are equal
return true;
}
if (file1.isDirectory() || file2.isDirectory()) {
// don't want to compare directory contents
throw new IOException("Can't compare directories, only files");
}
if (file1.getCanonicalFile().equals(file2.getCanonicalFile())) {
// same file
return true;
}
Reader input1 = null;
Reader input2 = null;
try {
if (charsetName == null) {
input1 = new InputStreamReader(new FileInputStream(file1));
input2 = new InputStreamReader(new FileInputStream(file2));
} else {
input1 = new InputStreamReader(new FileInputStream(file1), charsetName);
input2 = new InputStreamReader(new FileInputStream(file2), charsetName);
}
return IOUtils.contentEqualsIgnoreEOL(input1, input2);
} finally {
IOUtils.closeQuietly(input1);
IOUtils.closeQuietly(input2);
}
}本函数和上一条基本相同，区别在于：
Reader input1 = null;
Reader input2 = null;
try {
if (charsetName == null) {
input1 = new InputStreamReader(new FileInputStream(file1));
input2 = new InputStreamReader(new FileInputStream(file2));
} else {
input1 = new InputStreamReader(new FileInputStream(file1), charsetName);
input2 = new InputStreamReader(new FileInputStream(file2), charsetName);
}
return IOUtils.contentEqualsIgnoreEOL(input1, input2);
} finally {
IOUtils.closeQuietly(input1);
IOUtils.closeQuietly(input2);
}这里使用了charsetName，用以获取编码后的字符流
*学习：
InputStreamReader的创建（使用charsetName参数编码FileInputStream获取的字节）
3.
public static File toFile(URL url) {
if (url == null || !"file".equalsIgnoreCase(url.getProtocol())) {
return null;
} else {
String filename = url.getFile().replace('/', File.separatorChar);
filename = decodeUrl(filename);
return new File(filename);
}
}一个用于把file协议的url转换为File类型的函数
4.
static String decodeUrl(String url) {
String decoded = url;
if (url != null && url.indexOf('%') >= 0) {
int n = url.length();
StringBuffer buffer = new StringBuffer();
ByteBuffer bytes = ByteBuffer.allocate(n);
for (int i = 0; i < n;) {
if (url.charAt(i) == '%') {
try {
do {
byte octet = (byte) Integer.parseInt(url.substring(i + 1, i + 3), 16);
bytes.put(octet);
i += 3;
} while (i < n && url.charAt(i) == '%');
continue;
} catch (RuntimeException e) {
// malformed percent-encoded octet, fall through and
// append characters literally
} finally {
if (bytes.position() > 0) {
bytes.flip();
buffer.append(UTF8.decode(bytes).toString());
bytes.clear();
}
}
}
buffer.append(url.charAt(i++));
}
decoded = buffer.toString();
}
return decoded;
}转换URL出现问题时的优化处理
（存疑）
5.
public static File[] toFiles(URL[] urls) {
if (urls == null || urls.length == 0) {
return EMPTY_FILE_ARRAY;
}
File[] files = new File[urls.length];
for (int i = 0; i < urls.length; i++) {
URL url = urls[i];
if (url != null) {
if (url.getProtocol().equals("file") == false) {
throw new IllegalArgumentException(
"URL could not be converted to a File: " + url);
}
files[i] = toFile(url);
}
}
return files;
}Converts each of an array of
URL to a File. 刚才函数toFile()的数组版本
6.
public static URL[] toURLs(File[] files) throws IOException {
URL[] urls = new URL[files.length];
for (int i = 0; i < urls.length; i++) {
urls[i] = files[i].toURI().toURL();
}
return urls;
}Converts each of an array of
File to a URL.
7.
public static void copyFileToDirectory(File srcFile, File destDir) throws IOException {
copyFileToDirectory(srcFile, destDir, true);
}Copies a file to a directory preserving the file date.
8.
public static void copyFileToDirectory(File srcFile, File destDir, boolean preserveFileDate) throws IOException {
if (destDir == null) {
throw new NullPointerException("Destination must not be null");
}
if (destDir.exists() && destDir.isDirectory() == false) {
throw new IllegalArgumentException("Destination '" + destDir + "' is not a directory");
}
File destFile = new File(destDir, srcFile.getName());
copyFile(srcFile, destFile, preserveFileDate);
}刚才函数7的完整版本：
1.确保目标地址不是空的
2.确保目标地址存在，并且不是文件
3.对源文件和目标文件的保护在copyFile里做了，所以这里只做对目标目录的保护。
9.
public static void copyFile(File srcFile, File destFile) throws IOException {
copyFile(srcFile, destFile, true);
}
10.
public static void copyFile(File srcFile, File destFile,
boolean preserveFileDate) throws IOException {
if (srcFile == null) {
throw new NullPointerException("Source must not be null");
}
if (destFile == null) {
throw new NullPointerException("Destination must not be null");
}
if (srcFile.exists() == false) {
throw new FileNotFoundException("Source '" + srcFile + "' does not exist");
}
if (srcFile.isDirectory()) {
throw new IOException("Source '" + srcFile + "' exists but is a directory");
}
if (srcFile.getCanonicalPath().equals(destFile.getCanonicalPath())) {
throw new IOException("Source '" + srcFile + "' and destination '" + destFile + "' are the same");
}
File parentFile = destFile.getParentFile();
if (parentFile != null) {
if (!parentFile.mkdirs() && !parentFile.isDirectory()) {
throw new IOException("Destination '" + parentFile + "' directory cannot be created");
}
}
if (destFile.exists() && destFile.canWrite() == false) {
throw new IOException("Destination '" + destFile + "' exists but is read-only");
}
doCopyFile(srcFile, destFile, preserveFileDate);
}策略学习：
目标文件和源文件的保护监测
11.
public static long copyFile(File input, OutputStream output) throws IOException {
final FileInputStream fis = new FileInputStream(input);
try {
return IOUtils.copyLarge(fis, output);
} finally {
fis.close();
}
}从一个input文件中拷贝bytes进入output输出流，注意：
IOUtils.copyLarge(fis, output)这个方法内部使用了buffer，所以不需要使用BufferedInputStream
12.
private static void doCopyFile(File srcFile, File destFile, boolean preserveFileDate) throws IOException {
if (destFile.exists() && destFile.isDirectory()) {
throw new IOException("Destination '" + destFile + "' exists but is a directory");
}
FileInputStream fis = null;
FileOutputStream fos = null;
FileChannel input = null;
FileChannel output = null;
try {
fis = new FileInputStream(srcFile);
fos = new FileOutputStream(destFile);
input = fis.getChannel();
output = fos.getChannel();
long size = input.size();
long pos = 0;
long count = 0;
while (pos < size) {
count = size - pos > FILE_COPY_BUFFER_SIZE ? FILE_COPY_BUFFER_SIZE : size - pos;
pos += output.transferFrom(input, pos, count);
}
} finally {
IOUtils.closeQuietly(output);
IOUtils.closeQuietly(fos);
IOUtils.closeQuietly(input);
IOUtils.closeQuietly(fis);
}
if (srcFile.length() != destFile.length()) {
throw new IOException("Failed to copy full contents from '" +
srcFile + "' to '" + destFile + "'");
}
if (preserveFileDate) {
destFile.setLastModified(srcFile.lastModified());
}
}使用nio中的FileChannel进行复制（传输文件内容），调用IOUtils.closeQuietly()关闭filechannel和I/Ostream
最后用文件的length长度监测是否传输成功
16.
public static void copyDirectory (File
srcDir, File destDir,
FileFilter filter, boolean preserveFileDate) throws IOException
{
if (srcDir
== null) {
throw new NullPointerException("Source
must not be null");
}
if (destDir
== null) {
throw new NullPointerException("Destination
must not be null");
}
if (srcDir.exists()
== false) {
throw new FileNotFoundException("Source
'" + srcDir + "' does not exist");
}
if (srcDir.isDirectory()
== false) {
throw new IOException("Source
'" + srcDir + "' exists but is not a directory");
}
if (srcDir.getCanonicalPath().equals(destDir.getCanonicalPath()))
{
throw new IOException("Source
'" + srcDir + "' and destination '" +
destDir + "' are the same");
}
// Cater for destination being directory
within the source directory (see IO-141)
List<String> exclusionList = null;
if (destDir.getCanonicalPath().startsWith(srcDir.getCanonicalPath()))
{
File[] srcFiles = filter == null ?
srcDir.listFiles() : srcDir.listFiles(filter);
if (srcFiles
!= null && srcFiles.length >
0) {
exclusionList = new ArrayList<String>(srcFiles.length );
for (File
srcFile : srcFiles) {
File copiedFile = new File(destDir,
srcFile.getName());
exclusionList.add(copiedFile.getCanonicalPath());
}
}
}
doCopyDirectory(srcDir, destDir, filter, preserveFileDate, exclusionList);
}
这个函数加入了一个filter对复制操作的file加以过滤
注意：这里有一个假如destDir是srcDir的子目录的附加操作
// Cater for destination being directory
within the source directory (see IO-141)
List<String> exclusionList = null;
if (destDir.getCanonicalPath().startsWith(srcDir.getCanonicalPath()))
{
File[] srcFiles = filter == null ?
srcDir.listFiles() : srcDir.listFiles(filter);
if (srcFiles
!= null && srcFiles.length >
0) {
exclusionList = new ArrayList<String>(srcFiles.length );
for (File
srcFile : srcFiles) {
File copiedFile = new File(destDir,
srcFile.getName());
exclusionList.add(copiedFile.getCanonicalPath());
}
}
}
exclusionList是要排除的文件路径String列表（因为本来就在desDir里面），要作为参数传入下一个docopy()方法中
17.
private static void doCopyDirectory(File srcDir ,
File destDir, FileFilter filter,
boolean preserveFileDate,
List<String> exclusionList) throws IOException
{
// recurse
File[] srcFiles = filter == null ? srcDir.listFiles()
: srcDir.listFiles(filter);
if (srcFiles
== null) { //
null if abstract pathname does not denote a directory, or if an I/O error occurs
throw new IOException("Failed
to list contents of " + srcDir);
}
if (destDir.exists())
{
if (destDir.isDirectory()
== false) {
throw new IOException("Destination
'" + destDir + "' exists but is not a directory");
}
} else {
if (!destDir.mkdirs()
&& !destDir.isDirectory()) {
throw new IOException("Destination
'" + destDir + "' directory cannot be created");
}
}
if (destDir.canWrite()
== false) {
throw new IOException("Destination
'" + destDir + "' cannot be written to");
}
for (File
srcFile : srcFiles) {
File dstFile = new File(destDir,
srcFile.getName());
if (exclusionList
== null || !exclusionList.contains(srcFile.getCanonicalPath()))
{
if (srcFile.isDirectory())
{
doCopyDirectory(srcFile, dstFile, filter, preserveFileDate,
exclusionList);
} else {
doCopyFile(srcFile, dstFile, preserveFileDate);
}
}
}
// Do this last, as the above has probably
affected directory metadata
if (preserveFileDate)
{
destDir.setLastModified( srcDir.lastModified());
}
}
注意：
1.递归调用，反复打开子目录复制文件
2.排除列表的操作
20.
public static void copyInputStreamToFile(InputStream
source, File destination) throws IOException
{
try {
FileOutputStream output = openOutputStream(destination);
try {
IOUtils. copy(source, output);
output.close(); // don't swallow
close Exception if copy completes normally
} finally {
IOUtils. closeQuietly(output);
}
} finally {
IOUtils. closeQuietly(source);
}
}
使用 IOUtils. copy()函数复制source流到output流（目标文件输出流）
21.
public static void deleteDirectory(File
directory) throws IOException
{
if (!directory.exists())
{
return;
}
if (!isSymlink(directory))
{
cleanDirectory(directory);
}
if (!directory.delete())
{
String message =
"Unable to delete directory
" + directory + ".";
throw new IOException(message);
}
}
isSymlink(directory)貌似和windows没关系？？暂时存疑
调用cleanDirectory清空目录，然后删除目录本身
22.
public static boolean deleteQuietly (File
file) {
if (file
== null) {
return false ;
}
try {
if (file.isDirectory())
{
cleanDirectory(file);
}
} catch (Exception
ignored) {
}
try {
return file.delete();
} catch (Exception
ignored) {
return false ;
}
}
本身Doc的描述：
Deletes a file, never throwing an exception. If file is a directory, delete it and all sub-directories.
The difference between File.delete() and this method are:
- A directory to be deleted does not have to be empty. 亮点所在！！！！！！！！！
- No exceptions are thrown when a file or directory cannot be deleted.
23.
public static boolean directoryContains(final File
directory, final File child) throws IOException
{
// Fail fast against NullPointerException
if (directory
== null) {
throw new IllegalArgumentException("Directory
must not be null");
}
if (!directory.isDirectory())
{
throw new IllegalArgumentException("Not
a directory: " + directory);
}
if (child
== null) {
return false ;
}
if (!directory.exists()
|| !child.exists()) {
return false ;
}
// Canonicalize paths (normalizes relative
paths)
String canonicalParent = directory.getCanonicalPath();
String canonicalChild = child.getCanonicalPath();
return FilenameUtils.directoryContains(canonicalParent,
canonicalChild);
}
使用了FilenameUtils.directoryContains(canonicalParent,
canonicalChild)这个方法判断是否目录包含目标文件（非限定父子包含，可以是祖先后代关系）
24.
public static void cleanDirectory (File
directory) throws IOException
{
if (!directory.exists())
{
String message = directory + " does
not exist";
throw new IllegalArgumentException(message);
}
if (!directory.isDirectory())
{
String message = directory + " is
not a directory";
throw new IllegalArgumentException(message);
}
File[] files = directory.listFiles();
if (files
== null) { //
null if security restricted
throw new IOException("Failed
to list contents of " + directory);
}
IOException exception = null;
for (File
file : files) {
try {
forceDelete(file);
} catch (IOException
ioe) {
exception = ioe;
}
}
if (null !=
exception) {
throw exception;
}
}
调用forceDelete(file);删除文件或者文件夹
注意：
IOException exception = null ;
for (File
file : files) {
try {
forceDelete(file);
} catch (IOException
ioe) {
exception = ioe;
}
}
if (null !=
exception) {
throw exception;
}
这里是为了可以顺利抛出异常才这样写
25.
public static boolean waitFor(File
file, int seconds) {
int timeout
= 0;
int tick
= 0;
while (!file.exists())
{
if (tick++
>= 10) {
tick = 0;
if (timeout++
> seconds) {
return false ;
}
}
try {
Thread. sleep(100);
} catch (InterruptedException
ignore) {
// ignore exception
} catch (Exception
ex) {
break;
}
}
return true ;
}
等待一定时间，反复测试是否存在吗某一文件（可用于等待用户创建某一文件）
注意：
1.采用线程sleep(100)，使得1秒可以检查10次文件是否存在
2.这里过滤sleep操作引起的InterruptedException 异常，但是捕捉其他异常，发生则会break，这里个人觉得不太好，因为这样发生异常就会返回true
34.
public static void writeStringToFile(File
file, String data, Charset encoding, boolean append) throws IOException
{
OutputStream out = null;
try {
out = openOutputStream(file, append);
IOUtils. write(data, out, encoding);
out.close(); // don't swallow close
Exception if copy completes normally
} finally {
IOUtils. closeQuietly(out);
}
}
这里不明白的：
out.close(); // don't swallow close Exception
if copy completes normally
这个什么意思？
38.
public static void write(File
file, CharSequence data, Charset encoding, boolean append) throws IOException
{
String str = data == null ? null :
data.toString();
writeStringToFile(file, str ,
encoding, append);
}
CharSequence 接口实现类都可以使用
46.
public static void writeLines (File
file, String encoding, Collection<?> lines, String lineEnding, boolean append)
throws IOException
{
FileOutputStream out = null;
try {
out = openOutputStream(file, append);
final BufferedOutputStream
buffer = new BufferedOutputStream(out);
IOUtils. writeLines(lines, lineEnding, buffer, encoding);
buffer.flush();
out.close(); // don't swallow close
Exception if copy completes normally
} finally {
IOUtils. closeQuietly(out);
}
}
这里使用了IOUtils. writeLines(lines,
lineEnding, buffer, encoding);写入行，并且值得注意的是，可以用lineEnding指定行分隔符
49.
public static void forceDelete (File
file) throws IOException {
if (file.isDirectory())
{
deleteDirectory(file);
} else {
boolean filePresent
= file.exists();
if (!file.delete())
{
if (!filePresent){
throw new FileNotFoundException("File
does not exist: " + file);
}
String message =
"Unable to delete file:
" + file;
throw new IOException(message);
}
}
}
这里和刚才的deleteDirectory()有隐式递归调用，在目录和文件的区分处理上，假如是目录，就用deleteDirectory()继续打开，用以递归打开再调用forceDelete(),如此反复，可以做到删除所用文件
52.
private static void cleanDirectoryOnExit(File
directory) throws IOException
{
if (!directory.exists())
{
String message = directory + " does
not exist";
throw new IllegalArgumentException(message);
}
if (!directory.isDirectory())
{
String message = directory + " is
not a directory";
throw new IllegalArgumentException(message);
}
File[] files = directory.listFiles();
if (files
== null) { //
null if security restricted
throw new IOException("Failed
to list contents of " + directory);
}
IOException exception = null;
for (File
file : files) {
try {
forceDeleteOnExit(file);
} catch (IOException
ioe) {
exception = ioe;
}
}
if (null !=
exception) {
throw exception;
}
}
在JVM退出时清空，目录，其中调用到了File.deleteOnExit()
53.
public static void forceMkdir (File
directory) throws IOException
{
if (directory.exists())
{
if (!directory.isDirectory())
{
String message =
"File "
+ directory
+ " exists and is "
+ "not a directory.
Unable to create directory.";
throw new IOException(message);
}
} else {
if (!directory.mkdirs())
{
// Double-check that some other
thread or process hasn't made
// the directory in the background
if (!directory.isDirectory())
{
String message =
"Unable to create directory
" + directory;
throw new IOException(message);
}
}
}
}
存疑：
// Double-check that some other thread or process hasn't made
// the directory in the background
这是表达什么？
54.
public static long sizeOf(File
file) {
if (!file.exists())
{
String message = file + " does not
exist";
throw new IllegalArgumentException(message);
}
if (file.isDirectory())
{
return sizeOfDirectory(file);
} else {
return file.length();
}
}
返回一个File对象的byte大小，目录会递归调用，但是不会处理受限制的子目录
65.
public static long checksumCRC32(File
file) throws IOException {
CRC32 crc = new CRC32 ();
checksum(file, crc);
return crc.getValue();
}
存疑
CRC32是啥？
66.
public static Checksum
checksum(File file, Checksum checksum) throws IOException
{
if (file.isDirectory())
{
throw new IllegalArgumentException("Checksums
can't be computed on directories");
}
InputStream in = null;
try {
in = new CheckedInputStream(new FileInputStream(file),
checksum);
IOUtils. copy(in, new NullOutputStream());
} finally {
IOUtils. closeQuietly(in);
}
return checksum;
}
存疑
checksum是啥
67.
public static void moveDirectory (File
srcDir, File destDir) throws IOException
{
if (srcDir
== null) {
throw new NullPointerException("Source
must not be null");
}
if (destDir
== null) {
throw new NullPointerException("Destination
must not be null");
}
if (!srcDir.exists())
{
throw new FileNotFoundException("Source
'" + srcDir + "' does not exist");
}
if (!srcDir.isDirectory())
{
throw new IOException("Source
'" + srcDir + "' is not a directory");
}
if (destDir.exists())
{
throw new FileExistsException("Destination
'" + destDir + "' already exists");
}
boolean rename
= srcDir.renameTo(destDir);
if (!rename)
{
if (destDir.getCanonicalPath().startsWith(srcDir.getCanonicalPath()))
{
throw new IOException("Cannot
move directory: "+srcDir+ " to a subdirectory of
itself: "+destDir);
}
copyDirectory( srcDir, destDir );
deleteDirectory( srcDir );
if (srcDir.exists())
{
throw new IOException("Failed
to delete original directory '" + srcDir +
"' after copy to '" +
destDir + "'" );
}
}
}
注意：
1.boolean rename
= srcDir.renameTo(destDir);使用这个renameTo的操作移动，假如未成功再进行第二种移动操作（先复制，再删除）
2.不能移动父目录到子目录
3.删除不成功要抛出异常
72.
public static boolean isSymlink(File
file) throws IOException {
if (file
== null) {
throw new NullPointerException("File
must not be null");
}
if (FilenameUtils.isSystemWindows())
{
return false;
}
File fileInCanonicalDir = null;
if (file.getParent()
== null) {
fileInCanonicalDir = file;
} else {
File canonicalDir = file.getParentFile(). getCanonicalFile();
fileInCanonicalDir = new File(canonicalDir,
file.getName());
}
if (fileInCanonicalDir.getCanonicalFile().equals(fileInCanonicalDir.getAbsoluteFile()))
{
return false;
} else {
return true;
}
}
存疑
貌似和WINDOWS系统无关？不懂。。。
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