After working, the technology used changes with the changes of the project, sometimes C#, sometimes Java, and of course some other fragmented technologies. Overall, C# takes longer, followed by Java. I don't have any preference for languages. A language that can do work is a good language. And from an object-oriented perspective, I think there is no difference between C# and Java for me.
This article mainly reviews the content related to I/O operations in Java. I/O is also a basic feature of programming languages. I/O in Java is divided into two types, one is sequential reading and the other is random. Read.
Let’s look at sequential reading first. There are two ways to perform sequential reading. One is InputStream/OutputStream, which is an input and output stream that operates on bytes; the other is Reader/Writer, which operates on characters. The input and output streams of the operation.
Below we draw the structure of InputStream
FileInputStream: operates files, often used together with BufferedInputStream
PipedInputStream: can be used for inter-thread communication
ObjectInputStream: can be used for object serialization
ByteArrayInputStream: used to process input of byte arrays
LineNumberInputStream: can output the current line number and can be modified in the program
The following is the structure of OutputStream
PrintStream: Provides interfaces similar to print and println to output data
Let's take a look at how to use Stream to operate input and output.
Reading files using InputStream
Copy the code code as follows:
Use FileInputStream to 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();
}
Reading files using BufferedInputStream
Copy the code code as follows:
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();
}
Copy files using OutputStream
Copy the code code as follows:
Copy files using FileOutputStream
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();
}
}
Copy the code code as follows:
Copy files using BufferedOutputStream
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. We will give a complete and rigorous code later.
Let's take a look at the structure of Reader
The Reader here basically corresponds to the InputStream.
The structure of Writer is as follows
Let's look at some examples of using Reader or Writer
Use Reader to read file contents
Copy the code code as follows:
Use BufferedReader to 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();
}
Copy files using Writer
Copy the code code as follows:
Copy files using BufferedWriter
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();
}
}
Let's look at how to perform random access to files. RandomAccessFile is mainly used in Java to perform random operations on files.
Create a file of fixed size
Copy the code code as follows:
Create fixed-size files
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();
}
Write random data to a file
Copy the code code as follows:
Insert random 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
Copy the code code as follows:
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 files
Copy the code code as follows:
Copy files
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 the code code as follows:
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
Copy the code code as follows:
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
Copy the code code as follows:
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;
}
Split large files into multiple small files
Copy the code code as follows:
Split large files into multiple 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
Copy the code code as follows:
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 command
Copy the code code as follows:
Execute external command
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();
}
}
