log.java

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package com.j2medev.chapter3;

import java.util.Date;
import javax.microedition.rms.*;

public class Log {
    
    private RecordStore rs = null;
    public static final String LOG_NAME = "log";
    
    public Log() {
        //打开RecordStore对象rs
        try{
            rs = RecordStore.openRecordStore(LOG_NAME,true);
        }catch(RecordStoreException ex){
            ex.printStackTrace();
            //does nothing
        }
    }
    
    public void closeLog(){
        //关闭rs
        if(rs != null){
            try{
                rs.closeRecordStore();
            }catch(RecordStoreException ex){
                ex.printStackTrace();;
            }
        }
    }
    
    public void clearLog(){
        //清除所有rs中的记录
        if(rs != null){
            try{
                rs.closeRecordStore();
                RecordStore.deleteRecordStore(LOG_NAME);
            }catch(Exception ex){
                ex.printStackTrace();
            }
        }
    }
    
    public void log(String message){
        //记录方法调用的信息，形式为long:String。其中long代表方法调用时间
        String temp = new Date().getTime()+":"+message;
        try{
            byte[] data = temp.getBytes();
            rs.addRecord(data,0,data.length);
        }catch(RecordStoreException ex){
            ex.printStackTrace();
        }
    }
    
    public boolean isEmpty(){
        //判断rs中是否有数据
        try{
            int size = rs.getNumRecords();
            return (size == 0)?true:false;
        }catch(RecordStoreException ex){
            ex.printStackTrace();
            return true;
        }
    }
    
    public String[] getLogs(){
        //获取所有的记录信息
        try{
            //按照时间的升序取得记录
            RecordEnumeration re = rs.enumerateRecords(null,new MyComparator(),false);
            int length = re.numRecords();
            if(length == 0){
                return null;
            }else{
                String[] logs = new String[length];
                int i = 0;
                while(re.hasNextElement()){
                    //过滤掉字符串前面的long:
                    byte[] data = re.nextRecord();
                    String temp = new String(data);
                    int index = temp.indexOf(":");
                    logs[i++] = temp.substring(index+1,temp.length());
                }
                return logs;
            }
        }catch(RecordStoreException ex){
            ex.printStackTrace();
            return null;
        }
    }
    //自己定义的RecordComparator,按照时间顺序记录方法的执行先后
    private class MyComparator implements RecordComparator{
        
        public int compare(byte[] b1,byte[] b2){
            String s1 = new String(b1);
            String s2 = new String(b2);
            int i1 = s1.indexOf(":");
            int i2 = s2.indexOf(":");
            if(i1 == -1 || i2 == -1)
                return RecordComparator.FOLLOWS;
            long l1 = Long.parseLong(s1.substring(0,i1));
            long l2 = Long.parseLong(s2.substring(0,i2));
            if(l1 > l2){
                return RecordComparator.FOLLOWS;
            }else if (l1 < l2){
                return RecordComparator.PRECEDES;
            }else{
                return RecordComparator.EQUIVALENT;
            }
        }
    }
}