学步园

Q:

程序如下：
FileOutputStream output = new FileOutputStream("d:\\a.txt");
output.write(97);
output.close();

如果我原来的 d：\a.txt中有内容 asdfasdfasdfa
怎么样才能将 ascii码97的a添加到 文件内容后面？
有没有相应的API啊
我也想到先将文件内容取到StringBuilder，然后将a后缀到StringBuilder，我觉得应该又更好的办法，能用JDK API上的东西就用API上的东西

A:

有重载构造方法的！

public FileOutputStream(FileDescriptor fdObj)

Creates an output file stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.

First, if there is a security manager, its checkWrite method is called with the file descriptorfdObj argument as its argument.

Parameters:

fdObj - the file descriptor to be opened for writing

Throws:

SecurityException - if a security manager exists and itscheckWrite method denies write access to the file
descriptor

See Also:

SecurityManager.checkWrite(java.io.FileDescriptor)

Example:

FileOutputStream output = new FileOutputStream("d:\\a.txt",true); 

Example:

/*
  Append output to file using FileOutputStream
  This example shows how to append byte data to a file using write method of
  Java FileOutputStream object.
*/
 
import java.io.*;
 
public class AppendToFile {
 
public static void main(String[] args) {
 
String strFilePath = "C://FileIO//demo.txt";
 
try
{
/*
  * To append output to a file, use
  * FileOutputStream(String file, booean blnAppend) or
  * FileOutputStream(File file, booean blnAppend) constructor.
  *
  * If blnAppend is true, output will be appended to the existing content
  * of the file. If false, file will be overwritten.
  */
 
FileOutputStream fos = new FileOutputStream(strFilePath, true);
String strContent = "Append output to a file example";
 
fos.write(strContent.getBytes());
 
/*
  * Close FileOutputStream using,
  * void close() method of Java FileOutputStream class.
  *
  */
 
fos.close();
 
}
catch(FileNotFoundException ex)
{
System.out.println("FileNotFoundException : " + ex);
}
catch(IOException ioe)
{
System.out.println("IOException : " + ioe);
}
 
}
}