Java代码
import java.io.BufferedReader;  
import java.io.File;  
import java.io.FileInputStream;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.util.StringTokenizer;  

/**


* 取得linux系统下的cpu、内存信息
*  
* */
public final class LinuxSystemTool  
{  
   /**
   * get memory by used info
   *  
   * @return int[] result
   * result.length==4;int[0]=MemTotal;int[1]=MemFree;int[2]=SwapTotal;int[3]=SwapFree;
   * @throws IOException
   * @throws InterruptedException
   */
   public static int[] getMemInfo() throws IOException, InterruptedException  
   {  
      File file = new File("/proc/meminfo");  
      BufferedReader br = new BufferedReader(new InputStreamReader(  
      new FileInputStream(file)));  
      int[] result = new int[4];  
      String str = null;  
      StringTokenizer token = null;  
      while((str = br.readLine()) != null)  
      {  
         token = new StringTokenizer(str);  
         if(!token.hasMoreTokens())  
            continue;  
     
         str = token.nextToken();  
         if(!token.hasMoreTokens())  
            continue;  
     
         if(str.equalsIgnoreCase("MemTotal:"))  
            result[0] = Integer.parseInt(token.nextToken());  
         else if(str.equalsIgnoreCase("MemFree:"))  
            result[1] = Integer.parseInt(token.nextToken());  
         else if(str.equalsIgnoreCase("SwapTotal:"))  
            result[2] = Integer.parseInt(token.nextToken());  
         else if(str.equalsIgnoreCase("SwapFree:"))  
            result[3] = Integer.parseInt(token.nextToken());  
      }  
     
      return result;  
   }  

   /**
   * get memory by used info
   *  
   * @return float efficiency
   * @throws IOException
   * @throws InterruptedException
   */
   public static float getCpuInfo() throws IOException, InterruptedException  
   {  
      File file = new File("/proc/stat");  
      BufferedReader br = new BufferedReader(new InputStreamReader(  
      new FileInputStream(file)));  
      StringTokenizer token = new StringTokenizer(br.readLine());  
      token.nextToken();  
      int user1 = Integer.parseInt(token.nextToken());  
      int nice1 = Integer.parseInt(token.nextToken());  
      int sys1 = Integer.parseInt(token.nextToken());  
      int idle1 = Integer.parseInt(token.nextToken());  
     
      Thread.sleep(1000);  

      br = new BufferedReader(  
      new InputStreamReader(new FileInputStream(file)));  
      token = new StringTokenizer(br.readLine());  
      token.nextToken();  
      int user2 = Integer.parseInt(token.nextToken());  
      int nice2 = Integer.parseInt(token.nextToken());  
      int sys2 = Integer.parseInt(token.nextToken());  
      int idle2 = Integer.parseInt(token.nextToken());  

      return (float)((user2 + sys2 + nice2) - (user1 + sys1 + nice1)) / (float)((user2 + nice2 + sys2 + idle2) - (user1 + nice1 + sys1 + idle1));  
   }  
}  

/**
* 测试类
*  
* <p>@author javer QQ:84831612</p>
* @date 2005
*/
public class JaverTest  
{  
    public static void main(String[] args) throws Exception  
    {  
        int[] memInfo = LinuxSystemTool.getMemInfo();  
        System.out.println("MemTotal：" + memInfo[0]);  
        System.out.println("MemFree：" + memInfo[1]);  
        System.out.println("SwapTotal：" + memInfo[2]);  
        System.out.println("SwapFree：" + memInfo[3]);  

        System.out.println("CPU利用率：" + LinuxSystemTool.getCpuInfo());  
    }  
}

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

/**


* 取得linux系统下的cpu、内存信息
*
* */
public final class LinuxSystemTool
{
   /**
   * get memory by used info
   *
   * @return int[] result
   * result.length==4;int[0]=MemTotal;int[1]=MemFree;int[2]=SwapTotal;int[3]=SwapFree;
   * @throws IOException
   * @throws InterruptedException
   */
   public static int[] getMemInfo() throws IOException, InterruptedException
   {
      File file = new File("/proc/meminfo");
      BufferedReader br = new BufferedReader(new InputStreamReader(
      new FileInputStream(file)));
      int[] result = new int[4];
      String str = null;
      StringTokenizer token = null;
      while((str = br.readLine()) != null)
      {
         token = new StringTokenizer(str);
         if(!token.hasMoreTokens())
            continue;
  
         str = token.nextToken();
         if(!token.hasMoreTokens())
            continue;
  
         if(str.equalsIgnoreCase("MemTotal:"))
            result[0] = Integer.parseInt(token.nextToken());
         else if(str.equalsIgnoreCase("MemFree:"))
            result[1] = Integer.parseInt(token.nextToken());
         else if(str.equalsIgnoreCase("SwapTotal:"))
            result[2] = Integer.parseInt(token.nextToken());
         else if(str.equalsIgnoreCase("SwapFree:"))
            result[3] = Integer.parseInt(token.nextToken());
      }
  
      return result;
   }

   /**
   * get memory by used info
   *
   * @return float efficiency
   * @throws IOException
   * @throws InterruptedException
   */
   public static float getCpuInfo() throws IOException, InterruptedException
   {
      File file = new File("/proc/stat");
      BufferedReader br = new BufferedReader(new InputStreamReader(
      new FileInputStream(file)));
      StringTokenizer token = new StringTokenizer(br.readLine());
      token.nextToken();
      int user1 = Integer.parseInt(token.nextToken());
      int nice1 = Integer.parseInt(token.nextToken());
      int sys1 = Integer.parseInt(token.nextToken());
      int idle1 = Integer.parseInt(token.nextToken());
  
      Thread.sleep(1000);

      br = new BufferedReader(
      new InputStreamReader(new FileInputStream(file)));
      token = new StringTokenizer(br.readLine());
      token.nextToken();
      int user2 = Integer.parseInt(token.nextToken());
      int nice2 = Integer.parseInt(token.nextToken());
      int sys2 = Integer.parseInt(token.nextToken());
      int idle2 = Integer.parseInt(token.nextToken());

      return (float)((user2 + sys2 + nice2) - (user1 + sys1 + nice1)) / (float)((user2 + nice2 + sys2 + idle2) - (user1 + nice1 + sys1 + idle1));
   }
}

/**
* 测试类
*
* <p>@author javer QQ:84831612</p>
* @date 2005
*/
public class JaverTest
{
    public static void main(String[] args) throws Exception
    {
        int[] memInfo = LinuxSystemTool.getMemInfo();
        System.out.println("MemTotal：" + memInfo[0]);
        System.out.println("MemFree：" + memInfo[1]);
        System.out.println("SwapTotal：" + memInfo[2]);
        System.out.println("SwapFree：" + memInfo[3]);

        System.out.println("CPU利用率：" + LinuxSystemTool.getCpuInfo());
    }
} （http://people.ee.ethz.ch/~oetiker/webtools/mrtg/）就是一个很不错的选择。不过用mrtg就要装sysstat、apache、snmp、perl之类的东西。而且安装也要好几个步骤，似乎比较麻烦。本来也想直接调用sar、vmstat之类的命令，parse一下结果就算了。哪知道发现不同的版本的linux这些命令的结果也都是不一样。既然要按版本 parse它们的结果，那还不如直接去系统里面获得算了。于是研究了一下sysstat（http://freshmeat.net/projects/sysstat/）和gkrellm（http://gkrellm.net ）的源代码，找到监测性能的数据所在。