mystuinforeader.java

学生信息读系统（根据学生的学号从存储系统读取学生信息）： 姓名

//A inherit class of StudentInfoReader.It reads information
//of a student from a local file.
import java.io.File;
import java.io.RandomAccessFile;
import java.io.FileInputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class MyStuInfoReader extends StudentInfoReader
{
	//Show if this reading is successful.
	//Only this boolean value and readInfos(String) are true
	//This read will successful.
	public boolean canRead=false;
	
	//The information file
	protected File infors=null;
	
	//The indexs file.
	protected File indexs=null;
	
	//The index of the ID's information in the file infors to be read.
	private int index=0;
	
	//The length of the ID's information in the file infors to be read.
	private int length=0;
	
	RandomAccessFile ra=null;
	FileInputStream fin=null;
	FileChannel fc=null;
    
	//param file the file name for reading.
	public MyStuInfoReader(String file)
	{
		infors=new File("infos"+"\\"+file+".ino");
		indexs=new File("infos"+"\\"+file+".ind");
		if(!infors.exists()||!indexs.exists())
		{
			canRead=false;
		}
		else
		{
		    try
		    {
			    ra=new RandomAccessFile(infors,"r");
			    fin=new FileInputStream(indexs);
			    canRead=true;
		    }
		    catch(Exception e)
		    {
			    canRead=false;
		    }
		}
	}
	
	//inherit the abstract method.
	public char[] read(String stuID) throws Exception
	{
		setValue(stuID);
		char[] chars=new char[length/2];
		ra.seek(index);
		for(int i=0;i<chars.length;i++)
		{
		    chars[i]=ra.readChar();
		}
		return chars;
	}
	
	//Get the index and length values of the specified stuID's information 
	//in file infors from file indexs.
	protected void setValue(String id) throws Exception
	{
		fc=fin.getChannel();
		ByteBuffer b=ByteBuffer.allocate((int)fc.size());
		fc.read(b);
		String[] s1=new String[2];
		StringBuffer s=new StringBuffer();
		int i=0;
		b.position(0);
		while(b.position()<b.limit())
		{
			char c=b.getChar();
			i+=2;
			b.position(i);
			if(c=='/')
			{
				if(s.toString().equals(id))
				{
					s=null;
					s=new StringBuffer();
					int j=0;
					while(j<2)
					{
						c=b.getChar();
						if(c=='/')
						{
							s1[j]=s.toString();
							s=null;
							s=new StringBuffer();
							j++;
						}
						else
						{
							s.append(c);
						}
					}
					break;
				}
				else
				{
					s=null;
					s=new StringBuffer();
				}
			}
			else
			{
				s.append(c);
			}
		}
		index=Integer.decode(s1[0]).intValue();
		length=Integer.decode(s1[1]).intValue();
		fc.close();
	}
}