java IO操作大全

1.对一个文件添加

try {
BufferedWriter out = new BufferedWriter(new FileWriter("filename", true));
out.write("aString");
out.close();
} catch (IOException e) {
}

2.确定两个文件名路径指向同一个文件

<strong>File file1 = new File("./filename");
File file2 = new File("filename");

// Filename paths are not equal
boolean b = file1.equals(file2);      // false

// Normalize the paths
try {
file1 = file1.getCanonicalFile(); // c:\almanac1.4\filename
file2 = file2.getCanonicalFile(); // c:\almanac1.4\filename
} catch (IOException e) {
}

// Filename paths are now equal
b = file1.equals(file2);              // true</strong>

<strong> String path = File.separator + "a" + File.separator + "b";</strong>

<strong> public void copyDirectory(File srcDir, File dstDir) throws IOException {
if (srcDir.isDirectory()) {
if (!dstDir.exists()) {
dstDir.mkdir();
}

String[] children = srcDir.list();
for (int i=0; i<children.length; i++) {
copyDirectory(new File(srcDir, children[i]),
new File(dstDir, children[i]));
}
} else {
// This method is implemented in e1071 Copying a File
copyFile(srcDir, dstDir);
}
}
</strong>

文件间拷贝

// Copies src file to dst file.
// If the dst file does not exist, it is created
void copy(File src, File dst) throws IOException {
InputStream in = new FileInputStream(src);
OutputStream out = new FileOutputStream(dst);

// Transfer bytes from in to out
byte[] buf = new byte[1024];
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
in.close();
out.close();
}

6.创建目录

// Create a directory; all ancestor directories must exist
boolean success = (new File("directoryName")).mkdir();
if (!success) {
// Directory creation failed
}

// Create a directory; all non-existent ancestor directories are
// automatically created
success = (new File("directoryName")).mkdirs();
if (!success) {
// Directory creation failed
}

7.创建文件

<strong>try {
File file = new File("filename");

// Create file if it does not exist
boolean success = file.createNewFile();
if (success) {
// File did not exist and was created
} else {
// File already exists
}
} catch (IOException e) {
}</strong>

<strong>try {
// Create temp file.
File temp = File.createTempFile("pattern", ".suffix");

// Delete temp file when program exits.
temp.deleteOnExit();

// Write to temp file
BufferedWriter out = new BufferedWriter(new FileWriter(temp));
out.write("aString");
out.close();
} catch (IOException e) {
}</strong>

<strong>String curDir = System.getProperty("user.dir");</strong>

10.删除一个目录

// Delete an empty directory
boolean success = (new File("directoryName")).delete();
if (!success) {
// Deletion failed
}

// Deletes all files and subdirectories under dir.
// Returns true if all deletions were successful.
// If a deletion fails, the method stops attempting to delete and returns false.
public static boolean deleteDir(File dir) {
if (dir.isDirectory()) {
String[] children = dir.list();
for (int i=0; i<children.length; i++) {
boolean success = deleteDir(new File(dir, children[i]));
if (!success) {
return false;
}
}
}

// The directory is now empty so delete it
return dir.delete();
}

11.删除文件

boolean success = (new File("filename")).delete();
if (!success) {
// Deletion failed
}

12.反序列化一个对象

try {
// Deserialize from a file
File file = new File("filename.ser");
ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
// Deserialize the object
javax.swing.JButton button = (javax.swing.JButton) in.readObject();
in.close();

// Get some byte array data
byte[] bytes = getBytesFromFile(file);
// see e36 将文件读入字节数组 for the implementation of this method

// Deserialize from a byte array
in = new ObjectInputStream(new ByteArrayInputStream(bytes));
button = (javax.swing.JButton) in.readObject();
in.close();
} catch (ClassNotFoundException e) {
} catch (IOException e) {
}

13.实现一个可序列化的Singleton

public class MySingleton implements Serializable {
static MySingleton singleton = new MySingleton();

private MySingleton() {
}

// This method is called immediately after an object of this class is deserialized.
// This method returns the singleton instance.
protected Object readResolve() {
return singleton;
}
}

14.确定文件或目录是否存在

boolean exists = (new File("filename")).exists();
if (exists) {
// File or directory exists
} else {
// File or directory does not exist
}

15.将文件读入字节数组

public static byte[] getBytesFromFile(File file) throws IOException {
InputStream is = new FileInputStream(file);

// Get the size of the file
long length = file.length();

// You cannot create an array using a long type.
// It needs to be an int type.
// Before converting to an int type, check
// to ensure that file is not larger than Integer.MAX_VALUE.
if (length > Integer.MAX_VALUE) {
// File is too large
}

// Create the byte array to hold the data
byte[] bytes = new byte[(int)length];

// Read in the bytes
int offset = 0;
int numRead = 0;
while (offset < bytes.length
&& (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
offset += numRead;
}

// Ensure all the bytes have been read in
if (offset < bytes.length) {
throw new IOException("Could not completely read file "+file.getName());
}

// Close the input stream and return bytes
is.close();
return bytes;
}

16.在文件名路径和URL之间转换

// Create a file object
File file = new File("filename");

// Convert the file object to a URL
URL url = null;
try {
// The file need not exist. It is made into an absolute path
// by prefixing the current working directory
url = file.toURL();          // file:/d:/almanac1.4/java.io/filename
} catch (MalformedURLException e) {
}

// Convert the URL to a file object
file = new File(url.getFile());  // d:/almanac1.4/java.io/filename

// Read the file contents using the URL
try {
// Open an input stream
InputStream is = url.openStream();

// Read from is

is.close();
} catch (IOException e) {
// Could not open the file
}

17.从相对文件名路径获得绝对文件名路径

File file = new File("filename.txt");
file = file.getAbsoluteFile();  // c:\temp\filename.txt

file = new File("dir"+File.separatorChar+"filename.txt");
file = file.getAbsoluteFile();  // c:\temp\dir\filename.txt

file = new File(".."+File.separatorChar+"filename.txt");
file = file.getAbsoluteFile();  // c:\temp\..\filename.txt

// Note that filename.txt does not need to exist

18.列出目录下文件或者子目录

File dir = new File("directoryName");

String[] children = dir.list();
if (children == null) {
// Either dir does not exist or is not a directory
} else {
for (int i=0; i<children.length; i++) {
// Get filename of file or directory
String filename = children[i];
}
}

// It is also possible to filter the list of returned files.
// This example does not return any files that start with `.'.
FilenameFilter filter = new FilenameFilter() {
public boolean accept(File dir, String name) {
return !name.startsWith(".");
}
};
children = dir.list(filter);

// The list of files can also be retrieved as File objects
File[] files = dir.listFiles();

// This filter only returns directories
FileFilter fileFilter = new FileFilter() {
public boolean accept(File file) {
return file.isDirectory();
}
};
files = dir.listFiles(fileFilter);

19.得到文件大小

File file = new File("infilename");

// Get the number of bytes in the file
long length = file.length();

20.获得一个文件名路径的上一层路径

// Get the parent of a relative filename path
File file = new File("Ex1.java");
String parentPath = file.getParent();      // null
File parentDir = file.getParentFile();     // null

// Get the parents of an absolute filename path
file = new File("D:\\almanac\\Ex1.java");
parentPath = file.getParent();             // D:\almanac
parentDir = file.getParentFile();          // D:\almanac

parentPath = parentDir.getParent();        // D:\
parentDir = parentDir.getParentFile();     // D:\

parentPath = parentDir.getParent();        // null
parentDir = parentDir.getParentFile();     // null

21.确定文件名路径是文件还是目录

File dir = new File("directoryName");

boolean isDir = dir.isDirectory();
if (isDir) {
// dir is a directory
} else {
// dir is a file
}

22.获取并设置文件或目录的修改时间

File dir = new File("directoryName");

String[] children = dir.list();
if (children == null) {
// Either dir does not exist or is not a directory
} else {
for (int i=0; i<children.length; i++) {
// Get filename of file or directory
String filename = children[i];
}
}

// It is also possible to filter the list of returned files.
// This example does not return any files that start with `.'.
FilenameFilter filter = new FilenameFilter() {
public boolean accept(File dir, String name) {
return !name.startsWith(".");
}
};
children = dir.list(filter);

// The list of files can also be retrieved as File objects
File[] files = dir.listFiles();

// This filter only returns directories
FileFilter fileFilter = new FileFilter() {
public boolean accept(File file) {
return file.isDirectory();
}
};
files = dir.listFiles(fileFilter);

23.将文件或目录移动到另外的目录

// File (or directory) to be moved
File file = new File("filename");

// Destination directory
File dir = new File("directoryname");

// Move file to new directory
boolean success = file.renameTo(new File(dir, file.getName()));
if (!success) {
// File was not successfully moved
}

24.标记化java源码

try {
// Create the tokenizer to read from a file
FileReader rd = new FileReader("filename.java");
StreamTokenizer st = new StreamTokenizer(rd);

// Prepare the tokenizer for Java-style tokenizing rules
st.parseNumbers();
st.wordChars('_', '_');
st.eolIsSignificant(true);

// If whitespace is not to be discarded, make this call
st.ordinaryChars(0, ' ');

// These calls caused comments to be discarded
st.slashSlashComments(true);
st.slashStarComments(true);

// Parse the file
int token = st.nextToken();
while (token != StreamTokenizer.TT_EOF) {
token = st.nextToken();
switch (token) {
case StreamTokenizer.TT_NUMBER:
// A number was found; the value is in nval
double num = st.nval;
break;
case StreamTokenizer.TT_WORD:
// A word was found; the value is in sval
String word = st.sval;
break;
case '"':
// A double-quoted string was found; sval contains the contents
String dquoteVal = st.sval;
break;
case '\'':
// A single-quoted string was found; sval contains the contents
String squoteVal = st.sval;
break;
case StreamTokenizer.TT_EOL:
// End of line character found
break;
case StreamTokenizer.TT_EOF:
// End of file has been reached
break;
default:
// A regular character was found; the value is the token itself
char ch = (char)st.ttype;
break;
}
}
rd.close();
} catch (IOException e) {
}

25.从标准输入流中获取文本

try {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String str = "";
while (str != null) {
System.out.print("> prompt ");
str = in.readLine();
process(str);
}
} catch (IOException e) {
}

26.读取UTF-8编码数据

try {
BufferedReader in = new BufferedReader(
new InputStreamReader(new FileInputStream("infilename"), "UTF8"));
String str = in.readLine();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}

27.读取ISO Latin-1编码数据

try {
BufferedReader in = new BufferedReader(
new InputStreamReader(new FileInputStream("infilename"), "8859_1"));
String str = in.readLine();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}

28.从文件中获取文本

try {
BufferedReader in = new BufferedReader(new FileReader("infilename"));
String str;
while ((str = in.readLine()) != null) {
process(str);
}
in.close();
} catch (IOException e) {
}

29.重命名文件或目录

// File (or directory) with old name
File file = new File("oldname");

// File (or directory) with new name
File file2 = new File("newname");

// Rename file (or directory)
boolean success = file.renameTo(file2);
if (!success) {
// File was not successfully renamed
}

30.列出文件系统根目录

File[] roots = File.listRoots();
for (int i=0; i<roots.length; i++) {
process(roots[i]);
}

31.序列化一个对象

Object object = new javax.swing.JButton("push me");

try {
// Serialize to a file
ObjectOutput out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
out.writeObject(object);
out.close();

// Serialize to a byte array
ByteArrayOutputStream bos = new ByteArrayOutputStream() ;
out = new ObjectOutputStream(bos) ;
out.writeObject(object);
out.close();

// Get the bytes of the serialized object
byte[] buf = bos.toByteArray();
} catch (IOException e) {
}

32.强制文件更新保存到磁盘

try {
// Open or create the output file
FileOutputStream os = new FileOutputStream("outfilename");
FileDescriptor fd = os.getFD();

// Write some data to the stream
byte[] data = new byte[]{(byte)0xCA, (byte)0xFE, (byte)0xBA, (byte)0xBE};
os.write(data);

// Flush the data from the streams and writers into system buffers.
// The data may or may not be written to disk.
os.flush();

// Block until the system buffers have been written to disk.
// After this method returns, the data is guaranteed to have
// been written to disk.
fd.sync();
} catch (IOException e) {
}

33.遍历目录

// Process all files and directories under dir
public static void visitAllDirsAndFiles(File dir) {
process(dir);

if (dir.isDirectory()) {
String[] children = dir.list();
for (int i=0; i<children.length; i++) {
visitAllDirsAndFiles(new File(dir, children[i]));
}
}
}

// Process only directories under dir
public static void visitAllDirs(File dir) {
if (dir.isDirectory()) {
process(dir);

String[] children = dir.list();
for (int i=0; i<children.length; i++) {
visitAllDirs(new File(dir, children[i]));
}
}
}

// Process only files under dir
public static void visitAllFiles(File dir) {
if (dir.isDirectory()) {
String[] children = dir.list();
for (int i=0; i<children.length; i++) {
visitAllFiles(new File(dir, children[i]));
}
} else {
process(dir);
}
}

34.使用随机访问文件

try {
File f = new File("filename");
RandomAccessFile raf = new RandomAccessFile(f, "rw");

// Read a character
char ch = raf.readChar();

// Seek to end of file
raf.seek(f.length());

// Append to the end
raf.writeChars("aString");
raf.close();
} catch (IOException e) {
}

35.写入ISO Latin-1编码数据

try {
Writer out = new BufferedWriter(
new OutputStreamWriter(new FileOutputStream("outfilename"), "8859_1"));
out.write(aString);
out.close();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}

36.写入一个文件

try {
BufferedWriter out = new BufferedWriter(new FileWriter("outfilename"));
out.write("aString");
out.close();
} catch (IOException e) {
}

37.写入UTF-8编码数据

try {
Writer out = new BufferedWriter(new OutputStreamWriter(
new FileOutputStream("outfilename"), "UTF8"));
out.write(aString);
out.close();
} catch (UnsupportedEncodingException e) {
} catch (IOException e) {
}