Use of I and O based on Java review
- 2020-04-01 01:54:18
- OfStack
After work, the techniques used vary from project to project, sometimes in C#, sometimes in Java, and of course in other bits and pieces. In general, C# is a bit longer to use, followed by Java. I have no inclination to language, can work language, is a good language. And from an object-oriented perspective, I don't think C# is any different from Java to me.
I/O is a fundamental feature of the programming language. There are two types of I/O in Java, one is read sequentially, the other is read randomly.
So let's look at sequential reads first. There are two ways to do sequential reads. One is InputStream/OutputStream, which is the input and OutputStream that operates on bytes; The other is Reader/Writer, which is an input/output stream that operates on characters.
Now let's draw the structure of the InputStream
< img Alt = "" border = 0 SRC =" / / files.jb51.net/file_images/article/201305/201305080853201.png ">
FileInputStream: operates on files, often with a BufferedInputStream
PipedInputStream: can be used for inter-thread communication
ObjectInputStream: can be used for object serialization
ByteArrayInputStream: handles the input to a byte array
LineNumberInputStream: outputs the current number of lines and can be modified in the program
Below is the structure of the OutputStream
< img Alt = "" border = 0 SRC =" / / files.jb51.net/file_images/article/201305/201305080853332.png ">
PrintStream: provides interfaces like print and println to output data
Now let's look at how to manipulate the input and output using a Stream
Use the InputStream to read the file
use FileInputStream Read file information
public static byte[] readFileByFileInputStream(File file) throws IOException
{
ByteArrayOutputStream output = new ByteArrayOutputStream();
FileInputStream fis = null;
try
{
fis = new FileInputStream(file);
byte[] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
{
output.write(buffer, 0, bytesRead);
}
}
catch(Exception ex)
{
System.out.println("Error occurs during reading " + file.getAbsoluteFile());
}
finally
{
if (fis !=null) fis.close();
if (output !=null) output.close();
}
return output.toByteArray();
}
Read the file using the BufferedInputStream
public static byte[] readFileByBufferedInputStream(File file) throws Exception
{
FileInputStream fis = null;
BufferedInputStream bis = null;
ByteArrayOutputStream output = new ByteArrayOutputStream();
try
{
fis = new FileInputStream(file);
bis = new BufferedInputStream(fis);
byte[] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
{
output.write(buffer, 0, bytesRead);
}
}
catch(Exception ex)
{
System.out.println("Error occurs during reading " + file.getAbsoluteFile());
}
finally
{
if (fis != null) fis.close();
if (bis != null) bis.close();
if (output != null) output.close();
}
return output.toByteArray();
}
Use OutputStream to copy files
use FileOutputStream Copy the file
public static void copyFileByFileOutputStream(File file) throws IOException
{
FileInputStream fis = null;
FileOutputStream fos = null;
try
{
fis = new FileInputStream(file);
fos = new FileOutputStream(file.getName() + ".bak");
byte[] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead = fis.read(buffer,0,buffer.length)) != -1)
{
fos.write(buffer, 0, bytesRead);
}
fos.flush();
}
catch(Exception ex)
{
System.out.println("Error occurs during copying " + file.getAbsoluteFile());
}
finally
{
if (fis != null) fis.close();
if (fos != null) fos.close();
}
}
use BufferedOutputStream Copy the file
public static void copyFilebyBufferedOutputStream(File file)throws IOException
{
FileInputStream fis = null;
BufferedInputStream bis = null;
FileOutputStream fos = null;
BufferedOutputStream bos = null;
try
{
fis = new FileInputStream(file);
bis = new BufferedInputStream(fis);
fos = new FileOutputStream(file.getName() + ".bak");
bos = new BufferedOutputStream(fos);
byte[] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead = bis.read(buffer, 0, buffer.length)) != -1)
{
bos.write(buffer, 0, bytesRead);
}
bos.flush();
}
catch(Exception ex)
{
System.out.println("Error occurs during copying " + file.getAbsoluteFile());
}
finally
{
if (fis != null) fis.close();
if (bis != null) bis.close();
if (fos != null) fos.close();
if (bos != null) bos.close();
}
}
The code here handles exceptions very incompletely, and we'll show you the full, rigorous code later.
Let's look at the structure of the Reader
< img Alt = "" border = 0 SRC =" / / files.jb51.net/file_images/article/201305/20130508091103.png ">
The Reader here basically corresponds to the InputStream.
Writer has the following structure
< img Alt = "" border = 0 SRC =" / / files.jb51.net/file_images/article/201305/20130508085414.png ">
Let's look at some examples of using a Reader or Writer
Reader is used to read the contents of the file
use BufferedReader Read file contents
public static String readFile(String file)throws IOException
{
BufferedReader br = null;
StringBuffer sb = new StringBuffer();
try
{
br = new BufferedReader(new FileReader(file));
String line = null;
while((line = br.readLine()) != null)
{
sb.append(line);
}
}
catch(Exception ex)
{
System.out.println("Error occurs during reading " + file);
}
finally
{
if (br != null) br.close();
}
return sb.toString();
}
Use Writer to copy files
use BufferedWriter Copy the file
public static void copyFile(String file) throws IOException
{
BufferedReader br = null;
BufferedWriter bw = null;
try
{
br = new BufferedReader(new FileReader(file));
bw = new BufferedWriter(new FileWriter(file + ".bak"));
String line = null;
while((line = br.readLine())!= null)
{
bw.write(line);
}
}
catch(Exception ex)
{
System.out.println("Error occurs during copying " + file);
}
finally
{
if (br != null) br.close();
if (bw != null) bw.close();
}
}
Now let's look at how to randomly access files. RandomAccessFile is mainly used in Java to perform random operations on files.
Create a file of fixed size
Create a file of fixed size
public static void createFile(String file, int size) throws IOException
{
File temp = new File(file);
RandomAccessFile raf = new RandomAccessFile(temp, "rw");
raf.setLength(size);
raf.close();
}
Writes data randomly to a file
Randomly inserts data into a file
public static void writeFile(String file, byte[] content, int startPos, int contentLength) throws IOException
{
RandomAccessFile raf = new RandomAccessFile(new File(file), "rw");
raf.seek(startPos);
raf.write(content, 0, contentLength);
raf.close();
}
Next, let's look at some other common operations
Move files
Move files
public static boolean moveFile(String sourceFile, String destFile)
{
File source = new File(sourceFile);
if (!source.exists()) throw new RuntimeException("source file does not exist.");
File dest = new File(destFile);
if (!(new File(dest.getPath()).exists())) new File(dest.getParent()).mkdirs();
return source.renameTo(dest);
}
Copy the file
Copy the file
public static void copyFile(String sourceFile, String destFile) throws IOException
{
File source = new File(sourceFile);
if (!source.exists()) throw new RuntimeException("File does not exist.");
if (!source.isFile()) throw new RuntimeException("It is not file.");
if (!source.canRead()) throw new RuntimeException("File cound not be read.");
File dest = new File(destFile);
if (dest.exists())
{
if (dest.isDirectory()) throw new RuntimeException("Destination is a folder.");
else
{
dest.delete();
}
}
else
{
File parentFolder = new File(dest.getParent());
if (!parentFolder.exists()) parentFolder.mkdirs();
if (!parentFolder.canWrite()) throw new RuntimeException("Destination can not be written.");
}
FileInputStream fis = null;
FileOutputStream fos = null;
try
{
fis = new FileInputStream(source);
fos = new FileOutputStream(dest);
byte[] buffer = new byte[1024];
int bytesRead = 0;
while((bytesRead = fis.read(buffer, 0, buffer.length)) != -1)
{
fos.write(buffer, 0, bytesRead);
}
fos.flush();
}
catch(IOException ex)
{
System.out.println("Error occurs during copying " + sourceFile);
}
finally
{
if (fis != null) fis.close();
if (fos != null) fos.close();
}
}
Copy folder
Copy folder
public static void copyDir(String sourceDir, String destDir) throws IOException
{
File source = new File(sourceDir);
if (!source.exists()) throw new RuntimeException("Source does not exist.");
if (!source.canRead()) throw new RuntimeException("Source could not be read.");
File dest = new File(destDir);
if (!dest.exists()) dest.mkdirs();
File[] arrFiles = source.listFiles();
for(int i = 0; i < arrFiles.length; i++)
{
if (arrFiles[i].isFile())
{
BufferedReader reader = new BufferedReader(new FileReader(arrFiles[i]));
BufferedWriter writer = new BufferedWriter(new FileWriter(destDir + "/" + arrFiles[i].getName()));
String line = null;
while((line = reader.readLine()) != null) writer.write(line);
writer.flush();
reader.close();
writer.close();
}
else
{
copyDir(sourceDir + "/" + arrFiles[i].getName(), destDir + "/" + arrFiles[i].getName());
}
}
}
Delete folder
Delete folder
public static void del(String filePath)
{
File file = new File(filePath);
if (file == null || !file.exists()) return;
if (file.isFile())
{
file.delete();
}
else
{
File[] arrFiles = file.listFiles();
if (arrFiles.length > 0)
{
for(int i = 0; i < arrFiles.length; i++)
{
del(arrFiles[i].getAbsolutePath());
}
}
file.delete();
}
}
Get folder size
Get folder size
public static long getFolderSize(String dir)
{
long size = 0;
File file = new File(dir);
if (!file.exists()) throw new RuntimeException("dir does not exist.");
if (file.isFile()) return file.length();
else
{
String[] arrFileName = file.list();
for (int i = 0; i < arrFileName.length; i++)
{
size += getFolderSize(dir + "/" + arrFileName[i]);
}
}
return size;
}
Shred large files into smaller files
Cut large files into smaller files
public static void splitFile(String filePath, long unit) throws IOException
{
File file = new File(filePath);
if (!file.exists()) throw new RuntimeException("file does not exist.");
long size = file.length();
if (unit >= size) return;
int count = size % unit == 0 ? (int)(size/unit) : (int)(size/unit) + 1;
String newFile = null;
FileOutputStream fos = null;
FileInputStream fis =null;
byte[] buffer = new byte[(int)unit];
fis = new FileInputStream(file);
long startPos = 0;
String countFile = filePath + "_Count";
PrintWriter writer = new PrintWriter(new FileWriter( new File(countFile)));
writer.println(filePath + "t" + size);
for (int i = 1; i <= count; i++)
{
newFile = filePath + "_" + i;
startPos = (i - 1) * unit;
System.out.println("Creating " + newFile);
fos = new FileOutputStream(new File(newFile));
int bytesRead = fis.read(buffer, 0, buffer.length);
if (bytesRead != -1)
{
fos.write(buffer, 0, bytesRead);
writer.println(newFile + "t" + startPos + "t" + bytesRead);
}
fos.flush();
fos.close();
System.out.println("StartPos:" + i*unit + "; EndPos:" + (i*unit + bytesRead));
}
writer.flush();
writer.close();
fis.close();
}
Merge multiple small files into one large file
Merge multiple small files into one large file
public static void linkFiles(String countFile) throws IOException
{
File file = new File(countFile);
if (!file.exists()) throw new RuntimeException("Count file does not exist.");
BufferedReader reader = new BufferedReader(new FileReader(file));
String line = reader.readLine();
String newFile = line.split("t")[0];
long size = Long.parseLong(line.split("t")[1]);
RandomAccessFile raf = new RandomAccessFile(newFile, "rw");
raf.setLength(size);
FileInputStream fis = null;
byte[] buffer = null;
while((line = reader.readLine()) != null)
{
String[] arrInfo = line.split("t");
fis = new FileInputStream(new File(arrInfo[0]));
buffer = new byte[Integer.parseInt(arrInfo[2])];
long startPos = Long.parseLong(arrInfo[1]);
fis.read(buffer, 0, Integer.parseInt(arrInfo[2]));
raf.seek(startPos);
raf.write(buffer, 0, Integer.parseInt(arrInfo[2]));
fis.close();
}
raf.close();
}
Execute external commands
Execute external commands
public static void execExternalCommand(String command, String argument)
{
Process process = null;
try
{
process = Runtime.getRuntime().exec(command + " " + argument);
InputStream is = process.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line = null;
while((line = br.readLine()) != null)
{
System.out.println(line);
}
}
catch(Exception ex)
{
System.err.println(ex.getMessage());
}
finally
{
if (process != null) process.destroy();
}
}