Java File Operations

Last Update:2018-12-04 Source: Internet

Author: User

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File Creation/check and Deletion

<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> file creation, check, and deletion </title>
</Head>
<Body>
<%
String Path = request. getrealpath ("");
// Out. println (PATH );
File F = new file (path, "file.txt ");
// Out. println (f );
// Out. println (F. exists ());

If (F. exists () {// check whether file.txt exists
F. Delete (); // Delete the file.txt File
Out. println (path + "// file.txt exists and has been deleted. ");
} Else {
F. createnewfile (); // create a file named file.txt in the current directory.
Out. println (path + "// file.txt does not exist. It has been created. "); // Output the current directory path
}
%>

Directory creation/check and Deletion

<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> Directory Creation, check, and deletion </title>
</Head>
<Body>
<%
String Path = request. getrealpath ("");
Path = path + "// Sub"; // directory path to be created
File d = new file (PATH); // create a file object that represents the sub directory and obtain a reference
If (D. exists () {// check whether the sub directory exists
D. Delete ();
Out. println ("sub directory exists, deleted ");
} Else {
D. mkdir (); // create a sub directory
Out. println ("sub directory does not exist, created ");
}
%>
</Body>
</Html>

How to process virtual directories in JSP

<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> how to handle virtual directories in JSP </title>
</Head>
<Body>
Obtain the disk path corresponding to the virtual directory 
 <% = request. getrealpath ("/") %> 
 <% = request. getrealpath ("./") %> 
 <% = request. getrealpath ("../") %> 
</Body>
</Html>

File Attribute acquisition
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. util. Date, java. Io. *" %>
<HTML>
<Head>
<Title> File Attribute acquisition </title>
</Head>
<Body>
<%
String Path = request. getrealpath ("/");
File F = new file (path, "readdata.txt ");
If (F. exists ()){
%>
The attributes of <% = f. getname () %> are as follows: 
File length: <% = f. Length () %>
<% = F. isfile ()? "Yes file": "Not a file" %> 
<% = F. isdirectory ()? "Yes directory": "Not a directory" %> 
<% = F. Canread ()? "Readable": "unreadable" %> 
<% = F. canwrite ()? "Writable": "not writable" %> 
<% = F. ishidden ()? "Hidden file": "Not hidden file" %> 
The last modification date of the file is: <% = new date (F. lastmodified () %> 
<%
} Else {
F. createnewfile (); // create a file named readata.txt in the current directory.
%>
The attributes of <% = f. getname () %> are as follows: 
File length: <% = f. Length () %>
<% = F. isfile ()? "Yes file": "Not a file" %> 
<% = F. isdirectory ()? "Yes directory": "Not a directory" %> 
<% = F. Canread ()? "Readable": "unreadable" %> 
<% = F. canwrite ()? "Writable": "not writable" %> 
<% = F. ishidden ()? "Hidden file": "Not hidden file" %> 
The last modification date of the file is: <% = new date (F. lastmodified () %> 
<%
}
%>
</Body>
</Html>

How to retrieve files in a directory

<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> how to retrieve files in a directory-list files in a directory </title>
</Head>
<Body>
<%
String Path = request. getrealpath ("/");
File d = new file (PATH); // create the file object of the file in the current directory
File list [] = D. listfiles (); // retrieves an array of file objects representing all files in the directory
Out. println ("" + path + "files in the directory: ");
For (INT I = 0; I <list. length; I ++ ){
If (list . isfile ()){
Out. println (list . getname () + " ");
}
}
Out. println (" " + path + "directory Directory: ");
For (INT I = 0; I <list. length; I ++ ){
If (list . isdirectory ()){
Out. println (list . getname () + " ");
}
}
%>
</Body>
</Html>

Determines whether the file is blank.
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> determine whether a blank file is used </title>
</Head>
<Body>
<%
String Path = request. getrealpath ("/");
Out. println (PATH );
Filereader Fr = new filereader (path + "// atend.txt"); // create a filereader object and instantiate it as fr
// Use the read () method for the object generated by the filereader class to read the next character from the delimiter stream.
If (Fr. Read () =-1) // determines whether the object has been read to the end.
{
Out. Print ("there is no data in the atend.txt file ");
} Else {
Out. println ("data in the atend.txt file ");
}
Fr. Close ();
%>
</Body>
</Html>
 Read all file data 
<Ccid_nobr>
<Table width = "400" border = "1" cellspacing = "0" cellpadding = "2"
Bordercolorlight = "black" bordercolordark = "# ffffff" align = "center">
<Tr>
<TD bgcolor = "e6e6e6" class = "code" style = "font-size: 9pt">
<PRE> <ccid_code> <% @ page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *, java. Lang. *" %>
<HTML>
<Head>
<Title> Read all file data </title>
</Head>
<Body>
<%
String Path = request. getrealpath (".");
Filereader Fr = new filereader (path + "// readdata.txt ");
// The key is to determine whether the characters read have reached the end of the file during the reading process,
Whether the character is a broken line character in the file determines whether the character value is 13.
Int c = Fr. Read (); // read a character from the file
// Determine whether the object has been read to the end
While (C! =-1 ){
Out. Print (char) C); // output the read data
C = Fr. Read (); // continue reading data from the file
If (C = 13) {// determines whether the row is a broken line character
Out. Print (" "); // output branch label
Fr. Skip (1); // skip one character
// C = Fr. Read (); // read a character
}
}
Fr. Close ();
%>
</Body>
</Html>
Read data in one row
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> File Reading </title>
</Head>
<Body>
<%
String Path = request. getrealpath (""); // obtain the path of the current directory
Filereader Fr = new filereader (path + "// file // Inc // t.txt"); // create a filereader object and instantiate it as fr
Bufferedreader BR = new bufferedreader (FR); // create a bufferedreader object and instantiate it as Br
String line = Br. Readline (); // read a string from a file
// Judge whether the read string is not empty
While (line! = NULL ){
Out. println (LINE + " "); // output the data read from the file.
Line = Br. Readline (); // continue reading a row of data from the file
}
BR. Close (); // close the bufferedreader object
Fr. Close (); // close the file
%>
</Body>
</Html>

Skipping characters in the file is not read
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> skipped bytes are not read </title>
</Head>
<Body>
<%
String Path = request. getrealpath (".");
Filereader Fr = new filereader (path + "// readdata.txt ");
Fr. Skip (2); // skip 2 bytes
Int c = Fr. Read (); // read a byte
While (C! =-1 ){
Out. Print (char) C );
C = Fr. Read ();
}
Fr. Close ();
%>
</Body>
</Html>
Write data to a file
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> write data to a file </title>
</Head>
<Body>
<%
String Path = request. getrealpath (".");
Filewriter fw = new filewriter (path + "// writedata.txt"); // create a filewriter object and instantiate the FW
// Write a string to a file
FW. Write ("Hello! ");
FW. Write ("This book is JSP programming skills");
FW. Write ("Please advise! ");
FW. Write ("Email: stride@sina.com ");
FW. Close ();

Filereader Fr = new filereader (path + "// writedata.txt ");
Bufferedreader BR = new bufferedreader (FR); // create a bufferedreader object and instantiate it as Br
String line = Br. Readline ();
// Read a row of data
Out. println (LINE + " ");
BR. Close (); // close the bufferedreader object
Fr. Close ();
%>
</Body>
</Html>
Data branches that write files
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> data branches that will write files </title>
</Head>
<Body>
<%
String Path = request. getrealpath (".");
Filewriter fw = new filewriter (path + "// writedata.txt ");
Bufferedwriter BW = new bufferedwriter (FW );
Bw. Write ("Hello! ");
Bw. Write ("This book is" JSP programming skills ". ");
Bw. newline (); // disconnected
Bw. Write ("Please advise! ");
Bw. newline (); // disconnected
Bw. Write ("Email: stride@sina.com ");
Bw. Flush (); // update data to a file
FW. Close (); // close the file stream
Out. println ("written file content: ");
Filereader Fr = new filereader (path + "// writedata.txt ");
Bufferedreader BR = new bufferedreader (FR );
String line = Br. Readline (); // read a row of data
While (line! = NULL ){
Out. println (LINE + " ");
Line = Br. Readline ();
}
Fr. Close ();
%>
</Body>
</Html>
How to append data to a file
<% @ Page contenttype = "text/html; charset = gb2312" %>
<% @ Page import = "Java. Io. *" %>
<HTML>
<Head>
<Title> data branches that will write files </title>
</Head>
<Body>
<%
String Path = request. getrealpath (".");
Randomaccessfile Rf = new randomaccessfile (path + "// writedata.txt", "RW ");
// Define an object of the randomaccessfile class and instantiate it.
RF. Seek (RF. Length (); // move the pointer to the end of the file
RF. writebytes ("/nappend a line to the file! ");
RF. Close (); // close the file stream
Out. println ("written file content: ");
Filereader Fr = new filereader (path + "// writedata.txt ");
Bufferedreader BR = new bufferedreader (FR); // read the bufferedread object of the object
String line = Br. Readline ();
While (line! = NULL ){
Out. println (LINE + " ");
Line = Br. Readline ();
}
Fr. Close (); // close the file
%>
</Body>
</Html>

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