File

创建源

new File("path")

参数

描述

You can use the File object to generate persistent HTML or data files without using a database server. Information stored in a file is preserved when the server goes down.

Exercise caution when using the File object. An application can read and write files anywhere the operating system allows. If you create an application that writes to or reads from your file system, you should ensure that users cannot misuse this capability.

Specify the full path, including the filename, for the path parameter of the File object you want to create. The path must be an absolute path; do not use a relative path.

If the physical file specified in the path already exists, the JavaScript runtime engine references it when you call methods for the object. If the physical file does not exist, you can create it by calling the open method.

You can display the name and path of a physical file by calling the write function and passing it the name of the related File object.

A pointer indicates the current position in a file. If you open a file in the a or a+ mode, the pointer is initially positioned at the end of the file; otherwise, it is initially positioned at the beginning of the file. In an empty file, the beginning and end of the file are the same. Use the eof, getPosition, and setPosition methods to specify and evaluate the position of the pointer. See the open method for a描述 of the modes in which you can open a file.

You can use the prototype property of the File object to add a property to all File instances. If you do so, that addition applies to all File objects running in all applications on your server, not just in the single application that made the change. This allows you to expand the capabilities of this object for your entire server.

属性概览

方法概览

示例

userInfo = new File("info.txt") 示例 2. In the following example, the File object refers to a physical file with an absolute path:

userInfo = new File("c:\\data\\info.txt") 示例 3. The following example displays the name of a File object onscreen.

userInfo = new File("c:\\data\\info.txt")
write(userInfo)

属性

方法

语法

描述

Because byteToString is a static method of File, you always use it as File.byteToString(), rather than as a method of a File object you created.

If the argument you pass into the byteToString method is not a number, the method returns an empty string.

示例

// Create the source File object
source = new File("c:\data\source.txt") // If the source file opens successfully, create a target file
if (source.open("r")) {
   target = new File("c:\data\target.txt")
   target.open("w") // Copy the source file to the target
   while (!source.eof()) {
      data = File.byteToString(source.readByte())
      target.write(data);
   }
   source.close()
}
   target.close() This example is similar to the example used for the write method of File. However, this example reads bytes from the source file and converts them to strings, instead of reading strings from the source file.

参看

clearError

语法

描述

示例

参看

close

语法

描述

示例

参看

eof

语法

描述

A call to setPosition resulting in a location greater than fileObjectName.getLength places the pointer beyond the end of the file. Because all read operations also move the pointer, a read operation that reads the last byte of data (or character) in a file positions the pointer beyond the end of the file.

The eof method returns true if the pointer is beyond the end of the file; otherwise, it returns false.

示例

x = new File("c:\data\userInfo.txt")
if (x.open("r")) {
   while (!x.eof()) {
      line = x.readln()
      write(line+"<br>");
   }
   x.close();
}

参看

error

语法

返回

-1 if the file specified in fileObjectName is not open

Otherwise, the method returns a nonzero integer indicating the error status. Specific error status codes are platform-dependent. Refer to your operating system documentation for more information.

示例

userInput = new File("c:\data\input.txt")
userInput.open("w")
if (userInput.error() == 0) {
   fileIsOpen() }
else {
   fileIsNotOpen() }
userInput.clearError()

参看

exists

语法

返回

示例

dataFile = new File("c:\data\mytest.txt") if (dataFile.exists() ==true) {
   dataFile.open("w")
   writeData()
   dataFile.close()
}
else {
   noFile()
}

flush

语法

描述

Do not confuse the flush method of the File object with the top-level flush function. The flush function flushes a buffer of data and causes it to display in the client browser; the flush method flushes a buffer of data to a physical file.

示例

参看

getLength

语法

描述

示例

// Create the source File object
source = new File("c:\data\source.txt") // If the source file opens successfully, create a target file
if (source.open("r")) {
   target = new File("c:\data\target.txt")
   target.open("a")    // Copy the source file to the target
   for (var x = 0; x < source.getLength(); x++) {
      source.setPosition(x)
      data = source.read(1)
      target.write(data)
   }
   source.close()
}
   target.close()

getPosition

语法

返回

描述

示例

示例 1. In the following example, the first call to getPosition shows that the default pointer position is 0 in a file that is opened for reading. This example also shows that a call to the read method repositions the pointer.

dataFile = new File("c:\data\info.txt")
dataFile.open("r") write("The position is " + dataFile.getPosition() + "<BR>")
write("The next character is " + dataFile.read(1) + "<BR>")
write("The new position is " + dataFile.getPosition() + "<BR>") dataFile.close() This example displays the following information:

The position is 0
The next character is H
The new position is 1 示例 2. This example uses setPosition to position the pointer one byte from the end of the eleven-byte file, resulting in a pointer position of offset 10.

dataFile = new File("c:\data\info.txt")
dataFile.open("r") dataFile.setPosition(-1,2)
write("The position is " + dataFile.getPosition() + "<BR>")
write("The next character is " + dataFile.read(1) + "<BR>") dataFile.close() This example displays the following information:

The position is 10
The next character is d 示例 3. You can position the pointer beyond the end of the file and still evaluate getPosition successfully. However, a call to eof indicates that the pointer is beyond the end of the file.

dataFile.setPosition(1,2)
write("The position is " + dataFile.getPosition() + "<BR>")
write("The value of eof is " + dataFile.eof() + "<P>") This example displays the following information:

The position is 12
The value of eof is true

参看

open

语法

描述

The mode parameter is a string that specifies whether to open the file to read, write, or append data. You can optionally use the b parameter anytime you specify the mode. If you do so, the JavaScript runtime engine on the server opens the file as a binary file. If you do not use the b parameter, the runtime engine opens the file as a text file. The b parameter is available only on Windows platforms.

The possible values for mode are as follows:

• r[b] opens a file for reading. If the file exists, the method succeeds and returns true; otherwise, the method fails and returns false.
• w[b] opens a file for writing. If the file does not already exist, it is created; otherwise, it is overwritten. This method always succeeds and returns true.
• a[b] opens a file for appending (writing at the end of the file). If the file does not already exist, it is created. This method always succeeds and returns true.
• r+[b] opens a file for reading and writing. If the file exists, the method succeeds and returns true; otherwise, the method fails and returns false. Reading and writing commence at the beginning of the file. When writing, characters at the beginning of the file are overwritten.
• w+[b] opens a file for reading and writing. If the file does not already exist, it is created; otherwise, it is overwritten. This method always succeeds and returns true.
• a+[b] opens a file for reading and appending. If the file does not already exist, it is created. This method always succeeds and returns true. Reading and appending commence at the end of the file.

示例

userInfo = new File("c:\data\info.txt")
userInfo.open("w")
writeData()
userInfo.close() 示例 2. The following example opens a binary file so an application can read data from it. The application uses an if statement to take different actions depending on whether the open statement finds the specified file.

entryGraphic = new File("c:\data\splash.gif")
if (entryGraphic.open("rb") == true) {
   displayProcedure()
   }
else {
   errorProcedure()
   }
entryGraphic.close()

参看

read

语法

描述

The read method returns the characters it reads as a string.

Use the read method to read information from a text file; use the readByte method to read data from a binary file.

示例

dataFile = new File("c:\data\info.txt")
dataFile.open("r") write("The next character is " + dataFile.read(1) + "<BR>")
dataFile.setPosition(6)
write("The next five characters are " + dataFile.read(5) + "<BR>") dataFile.close() This example displays the following information:

The next character is H
The next five characters are World

参看

readByte

语法

描述

The readByte method returns the byte it reads as a number. If the pointer is at the end of the file when you issue readByte, the method returns -1.

Use the readByte method to read information from a binary file. You can use the readByte method to read from a text file, but you must use the byteToString method to convert the value to a string. Generally it is better to use the read method to read information from a text file.

You can use the writeByte method to write data read by the readByte method to a file.

示例

// Create the source File object
source = new File("c:\data\source.gif") // If the source file opens successfully, create a target file
if (source.open("rb")) {
   target = new File("c:\data\target.gif")
   target.open("wb") // Copy the source file to the target
   while (!source.eof()) {
      data = source.readByte()
      target.writeByte(data);
   }
   source.close();
}
target.close()

参看

readln

语法

描述

The readln method returns the characters it reads as a string.

The line separator characters ("\r" and "\n" on Windows platforms and "\n" on UNIX platforms) are not included in the string that the readln method returns. The \r character is skipped; \n determines the actual end of the line.

Use the readln method to read information from a text file; use the readByte method to read data from a binary file. You can use the writeln method to write data read by the readln method to a file.

示例

参看

setPosition

语法

描述

The position argument is a positive or negative integer that moves the pointer the specified number of bytes relative to the reference argument. Position 0 represents the beginning of a file. The end of a file is indicated by fileObjectName.getLength().

The optional reference argument is one of the following values, indicating the reference point for position:

• 0: relative to beginning of file.
• 1: relative to current position.
• 2: relative to end of file.
• Other (or unspecified): relative to beginning of file.

示例

The position is 10
The next character is d 示例 1. This example moves the pointer from the beginning of the file to offset 10. Because no value for reference is supplied, the JavaScript runtime engine assumes it is 0.

dataFile = new File("c:\data\info.txt")
dataFile.open("r") dataFile.setPosition(10)
write("The position is " + dataFile.getPosition() + "<BR>")
write("The next character is " + dataFile.read(1) + "<P>") dataFile.close() 示例 2. This example moves the pointer from the end of the file to offset 10.

dataFile = new File("c:\data\info.txt")
dataFile.open("r") dataFile.setPosition(-1,2)
write("The position is " + dataFile.getPosition() + "<BR>")
write("The next character is " + dataFile.read(1) + "<P>") dataFile.close()

参看

stringToByte

语法

描述

Because stringToByte is a static method of File, you always use it as File.stringToByte(), rather than as a method of a File object you created.

If this method succeeds, it returns the numeric value of the first character of the input string; if it fails, it returns 0.

示例

write("The stringToByte value of Hello = " +
   File.stringToByte("Hello") + "<BR>")
write("Returning that value to byteToString = " +
   File.byteToString(File.stringToByte("Hello")) + "<P>") The previous example displays the following information:

The stringToByte value of Hello = 72
Returning that value to byteToString = H

参看

write

语法

描述

Use the write method to write data to a text file; use the writeByte method to write data to a binary file. You can use the read method to read data from a file to a string for use with the write method.

Do not confuse the write method of the File object with the write function. The write function outputs data to the client browser; the write method outputs data to a physical file on the server.

示例

// Create the source File object
source = new File("c:\data\source.txt") // If the source file opens successfully, create a target file
if (source.open("r")) {
   target = new File("c:\data\target.txt")
   target.open("w") // Copy the source file to the target
   while (!source.eof()) {
      data = source.read(1)
      target.write(data);
   }
   source.close();
}
   target.flush()
   target.close()

参看

writeByte

语法

描述

Use the writeByte method to write data to a binary file; use the write method to write data to a text file. You can use the readByte method to read bytes of data from a file to numeric values for use with the writeByte method.

示例

参看

writeln

语法

描述

Use the writeln method to write data to a text file; use the writeByte method to write data to a binary file. You can use the readln method to read data from a file to a string for use with the writeln method.

示例

// Create the source File object
source = new File("c:\data\source.txt") // If the source file opens successfully, create a target file
if (source.open("r")) {
   target = new File("c:\data\target.txt")
   target.open("w") // Copy the source file to the target
   while (!source.eof()) {
      data = source.readln()
      target.writeln(data);
   }
   source.close();
}
   target.close() Note that the readln method ignores the carriage return/line feed characters when it reads a line from a file. The writeln method appends these characters to the string that it writes.

参看