最近做個項目，就是要取得cpu占有率等等的系統信息，一開始以為要用動態鏈接庫了，但后來發現可以像下面這樣做，不去調用jni，這樣省去了很多看新技術的時間o(∩_∩)o...

在java中，可以獲得總的物理內存、剩余的物理內存、已使用的物理內存等信息，下面例子可以取得這些信息，并且獲得在Windows下的內存使用率。
     首先編寫一個MonitorInfoBean類，用來裝載監控的一些信息，包括物理內存、剩余的物理內存、已使用的物理內存、內存使用率等字段，該類的代碼如下：

Java代碼 
package  com.amgkaka.performance;  
  
/** */ /**  
 * 監視信息的JavaBean類.  
 * @author  amg  
 * @version 1.0   
 * Creation date: 2008-4-25 - 上午10:37:00  
 */   
public   class  MonitorInfoBean {  
    /** */ /** 可使用內存. */   
    PRivate   long  totalMemory;  
      
    /** */ /** 剩余內存. */   
    private   long  freeMemory;  
      
    /** */ /** 最大可使用內存. */   
    private   long  maxMemory;  
      
    /** */ /** 操作系統. */   
    private  String osName;  
      
    /** */ /** 總的物理內存. */   
    private   long  totalMemorySize;  
      
    /** */ /** 剩余的物理內存. */   
    private   long  freePhysicalMemorySize;  
      
    /** */ /** 已使用的物理內存. */   
    private   long  usedMemory;  
      
    /** */ /** 線程總數. */   
    private   int  totalThread;  
      
    /** */ /** cpu使用率. */   
    private   double  cpuRatio;  
  
    public   long  getFreeMemory() {  
        return  freeMemory;  
    }  
  
    public   void  setFreeMemory( long  freeMemory) {  
        this .freeMemory = freeMemory;  
    }  
  
    public   long  getFreePhysicalMemorySize() {  
        return  freePhysicalMemorySize;  
    }  
  
    public   void  setFreePhysicalMemorySize( long  freePhysicalMemorySize) {  
        this .freePhysicalMemorySize = freePhysicalMemorySize;  
    }  
  
    public   long  getMaxMemory() {  
        return  maxMemory;  
    }  
  
    public   void  setMaxMemory( long  maxMemory) {  
        this .maxMemory = maxMemory;  
    }  
  
    public  String getOsName() {  
        return  osName;  
    }  
  
    public   void  setOsName(String osName) {  
        this .osName = osName;  
    }  
  
    public   long  getTotalMemory() {  
        return  totalMemory;  
    }  
  
    public   void  setTotalMemory( long  totalMemory) {  
        this .totalMemory = totalMemory;  
    }  
  
    public   long  getTotalMemorySize() {  
        return  totalMemorySize;  
    }  
  
    public   void  setTotalMemorySize( long  totalMemorySize) {  
        this .totalMemorySize = totalMemorySize;  
    }  
  
    public   int  getTotalThread() {  
        return  totalThread;  
    }  
  
    public   void  setTotalThread( int  totalThread) {  
        this .totalThread = totalThread;  
    }  
  
    public   long  getUsedMemory() {  
        return  usedMemory;  
    }  
  
    public   void  setUsedMemory( long  usedMemory) {  
        this .usedMemory = usedMemory;  
    }  
  
    public   double  getCpuRatio() {  
        return  cpuRatio;  
    }  
  
    public   void  setCpuRatio( double  cpuRatio) {  
        this .cpuRatio = cpuRatio;  
    }  
}  
package com.amgkaka.performance;

/** *//**
 * 監視信息的JavaBean類.
 * @author  amg
 * @version 1.0
 * Creation date: 2008-4-25 - 上午10:37:00
 */
public class MonitorInfoBean {
    /** *//** 可使用內存. */
    private long totalMemory;
   
    /** *//** 剩余內存. */
    private long freeMemory;
   
    /** *//** 最大可使用內存. */
    private long maxMemory;
   
    /** *//** 操作系統. */
    private String osName;
   
    /** *//** 總的物理內存. */
    private long totalMemorySize;
   
    /** *//** 剩余的物理內存. */
    private long freePhysicalMemorySize;
   
    /** *//** 已使用的物理內存. */
    private long usedMemory;
   
    /** *//** 線程總數. */
    private int totalThread;
   
    /** *//** cpu使用率. */
    private double cpuRatio;

    public long getFreeMemory() {
        return freeMemory;
    }

    public void setFreeMemory(long freeMemory) {
        this.freeMemory = freeMemory;
    }

    public long getFreePhysicalMemorySize() {
        return freePhysicalMemorySize;
    }

    public void setFreePhysicalMemorySize(long freePhysicalMemorySize) {
        this.freePhysicalMemorySize = freePhysicalMemorySize;
    }

    public long getMaxMemory() {
        return maxMemory;
    }

    public void setMaxMemory(long maxMemory) {
        this.maxMemory = maxMemory;
    }

    public String getOsName() {
        return osName;
    }

    public void setOsName(String osName) {
        this.osName = osName;
    }

    public long getTotalMemory() {
        return totalMemory;
    }

    public void setTotalMemory(long totalMemory) {
        this.totalMemory = totalMemory;
    }

    public long getTotalMemorySize() {
        return totalMemorySize;
    }

    public void setTotalMemorySize(long totalMemorySize) {
        this.totalMemorySize = totalMemorySize;
    }

    public int getTotalThread() {
        return totalThread;
    }

    public void setTotalThread(int totalThread) {
        this.totalThread = totalThread;
    }

    public long getUsedMemory() {
        return usedMemory;
    }

    public void setUsedMemory(long usedMemory) {
        this.usedMemory = usedMemory;
    }

    public double getCpuRatio() {
        return cpuRatio;
    }

    public void setCpuRatio(double cpuRatio) {
        this.cpuRatio = cpuRatio;
    }
}
接著編寫一個獲得當前的監控信息的接口，該類的代碼如下所示：

Java代碼 
package  com.amgkaka.performance;  
  
/** */ /**  
 * 獲取系統信息的業務邏輯類接口.  
 * @author amg * @version 1.0   
 * Creation date: 2008-3-11 - 上午10:06:06  
 */   
public   interface  IMonitorService {  
    /** */ /**  
     * 獲得當前的監控對象.  
     * @return 返回構造好的監控對象  
     * @throws Exception  
     * @author amgkaka  
     * Creation date: 2008-4-25 - 上午10:45:08  
     */   
    public  MonitorInfoBean getMonitorInfoBean()  throws  Exception;  
  
}  
package com.amgkaka.performance;

/** *//**
 * 獲取系統信息的業務邏輯類接口.
 * @author amg * @version 1.0
 * Creation date: 2008-3-11 - 上午10:06:06
 */
public interface IMonitorService {
    /** *//**
     * 獲得當前的監控對象.
     * @return 返回構造好的監控對象
     * @throws Exception
     * @author amgkaka
     * Creation date: 2008-4-25 - 上午10:45:08
     */
    public MonitorInfoBean getMonitorInfoBean() throws Exception;

}  該類的實現類MonitorServiceImpl如下所示：

Java代碼 
package  com.amgkaka.performance;  
  
import  java.io.InputStreamReader;  
import  java.io.LineNumberReader;  
  
import  sun.management.ManagementFactory;  
  
import  com.sun.management.OperatingSystemMXBean;  
  
/** */ /**  
 * 獲取系統信息的業務邏輯實現類.  
 * @author amg * @version 1.0 Creation date: 2008-3-11 - 上午10:06:06  
 */   
public   class  MonitorServiceImpl  implements  IMonitorService {  
    //可以設置長些，防止讀到運行此次系統檢查時的cpu占用率，就不準了   
    private   static   final   int  CPUTIME =  5000 ;  
  
    private   static   final   int  PERCENT =  100 ;  
  
    private   static   final   int  FAULTLENGTH =  10 ;  
  
    /** */ /**  
     * 獲得當前的監控對象.  
     * @return 返回構造好的監控對象  
     * @throws Exception  
     * @author amg     * Creation date: 2008-4-25 - 上午10:45:08  
     */   
    public  MonitorInfoBean getMonitorInfoBean()  throws  Exception {  
        int  kb =  1024 ;  
          
        // 可使用內存   
        long  totalMemory = Runtime.getRuntime().totalMemory() / kb;  
        // 剩余內存   
        long  freeMemory = Runtime.getRuntime().freeMemory() / kb;  
        // 最大可使用內存   
        long  maxMemory = Runtime.getRuntime().maxMemory() / kb;  
  
        OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory  
                .getOperatingSystemMXBean();  
  
        // 操作系統   
        String osName = System.getProperty("os.name" );  
        // 總的物理內存   
        long  totalMemorySize = osmxb.getTotalPhysicalMemorySize() / kb;  
        // 剩余的物理內存   
        long  freePhysicalMemorySize = osmxb.getFreePhysicalMemorySize() / kb;  
        // 已使用的物理內存   
        long  usedMemory = (osmxb.getTotalPhysicalMemorySize() - osmxb  
                .getFreePhysicalMemorySize())  
                / kb;  
  
        // 獲得線程總數   
        ThreadGroup parentThread;  
        for  (parentThread = Thread.currentThread().getThreadGroup(); parentThread  
                .getParent() != null ; parentThread = parentThread.getParent())  
            ;  
        int  totalThread = parentThread.activeCount();  
  
        double  cpuRatio =  0 ;  
        if  (osName.toLowerCase().startsWith( "windows" )) {  
            cpuRatio = this .getCpuRatioForWindows();  
        }  
          
        // 構造返回對象   
        MonitorInfoBean infoBean = new  MonitorInfoBean();  
        infoBean.setFreeMemory(freeMemory);  
        infoBean.setFreePhysicalMemorySize(freePhysicalMemorySize);  
        infoBean.setMaxMemory(maxMemory);  
        infoBean.setOsName(osName);  
        infoBean.setTotalMemory(totalMemory);  
        infoBean.setTotalMemorySize(totalMemorySize);  
        infoBean.setTotalThread(totalThread);  
        infoBean.setUsedMemory(usedMemory);  
        infoBean.setCpuRatio(cpuRatio);  
        return  infoBean;  
    }  
  
    /** */ /**  
     * 獲得CPU使用率.  
     * @return 返回cpu使用率  
     * @author amg     * Creation date: 2008-4-25 - 下午06:05:11  
     */   
    private   double  getCpuRatioForWindows() {  
        try  {  
            String procCmd = System.getenv("windir" )  
                    + "//system32//wbem//wmic.exe process get Caption,CommandLine,"   
                    + "KernelModeTime,ReadOperationCount,ThreadCount,UserModeTime,WriteOperationCount" ;  
            // 取進程信息   
            long [] c0 = readCpu(Runtime.getRuntime().exec(procCmd));  
            Thread.sleep(CPUTIME);  
            long [] c1 = readCpu(Runtime.getRuntime().exec(procCmd));  
            if  (c0 !=  null  && c1 !=  null ) {  
                long  idletime = c1[ 0 ] - c0[ 0 ];  
                long  busytime = c1[ 1 ] - c0[ 1 ];  
                return  Double.valueOf(  
                        PERCENT * (busytime) / (busytime + idletime))  
                        .doubleValue();  
            } else  {  
                return   0.0 ;  
            }  
        } catch  (Exception ex) {  
            ex.printStackTrace();  
            return   0.0 ;  
        }  
    }  
  
    /** */ /**  
     * 讀取CPU信息.  
     * @param proc  
     * @return  
     * @author amg     * Creation date: 2008-4-25 - 下午06:10:14  
     */   
    private   long [] readCpu( final  Process proc) {  
        long [] retn =  new   long [ 2 ];  
        try  {  
            proc.getOutputStream().close();  
            InputStreamReader ir = new  InputStreamReader(proc.getInputStream());  
            LineNumberReader input = new  LineNumberReader(ir);  
            String line = input.readLine();  
            if  (line ==  null  || line.length() < FAULTLENGTH) {  
                return   null ;  
            }  
            int  capidx = line.indexOf( "Caption" );  
            int  cmdidx = line.indexOf( "CommandLine" );  
            int  rocidx = line.indexOf( "ReadOperationCount" );  
            int  umtidx = line.indexOf( "UserModeTime" );  
            int  kmtidx = line.indexOf( "KernelModeTime" );  
            int  wocidx = line.indexOf( "WriteOperationCount" );  
            long  idletime =  0 ;  
            long  kneltime =  0 ;  
            long  usertime =  0 ;  
            while  ((line = input.readLine()) !=  null ) {  
                if  (line.length() < wocidx) {  
                    continue ;  
                }  
                // 字段出現順序：Caption,CommandLine,KernelModeTime,ReadOperationCount,   
                // ThreadCount,UserModeTime,WriteOperation   
                String caption = Bytes.substring(line, capidx, cmdidx - 1 )  
                        .trim();  
                String cmd = Bytes.substring(line, cmdidx, kmtidx - 1 ).trim();  
                if  (cmd.indexOf( "wmic.exe" ) >=  0 ) {  
                    continue ;  
                }  
                // log.info("line="+line);   
                if  (caption.equals( "System Idle Process" )  
                        || caption.equals("System" )) {  
                    idletime += Long.valueOf(  
                            Bytes.substring(line, kmtidx, rocidx - 1 ).trim())  
                            .longValue();  
                    idletime += Long.valueOf(  
                            Bytes.substring(line, umtidx, wocidx - 1 ).trim())  
                            .longValue();  
                    continue ;  
                }  
  
                kneltime += Long.valueOf(  
                        Bytes.substring(line, kmtidx, rocidx - 1 ).trim())  
                        .longValue();  
                usertime += Long.valueOf(  
                        Bytes.substring(line, umtidx, wocidx - 1 ).trim())  
                        .longValue();  
            }  
            retn[0 ] = idletime;  
            retn[1 ] = kneltime + usertime;  
            return  retn;  
        } catch  (Exception ex) {  
            ex.printStackTrace();  
        } finally  {  
            try  {  
                proc.getInputStream().close();  
            } catch  (Exception e) {  
                e.printStackTrace();  
            }  
        }  
        return   null ;  
    }  
      
    /** */ /**  
     * 測試方法.  
     * @param args  
     * @throws Exception  
     * @author amg     * Creation date: 2008-4-30 - 下午04:47:29  
     */   
    public   static   void  main(String[] args)  throws  Exception {  
        IMonitorService service = new  MonitorServiceImpl();  
        MonitorInfoBean monitorInfo = service.getMonitorInfoBean();  
        System.out.println("cpu占有率="  + monitorInfo.getCpuRatio());  
          
        System.out.println("可使用內存="  + monitorInfo.getTotalMemory());  
        System.out.println("剩余內存="  + monitorInfo.getFreeMemory());  
        System.out.println("最大可使用內存="  + monitorInfo.getMaxMemory());  
          
        System.out.println("操作系統="  + monitorInfo.getOsName());  
        System.out.println("總的物理內存="  + monitorInfo.getTotalMemorySize() +  "kb" );  
        System.out.println("剩余的物理內存="  + monitorInfo.getFreeMemory() +  "kb" );  
        System.out.println("已使用的物理內存="  + monitorInfo.getUsedMemory() +  "kb" );  
        System.out.println("線程總數="  + monitorInfo.getTotalThread() +  "kb" );  
    }  
}  
package com.amgkaka.performance;

import java.io.InputStreamReader;
import java.io.LineNumberReader;

import sun.management.ManagementFactory;

import com.sun.management.OperatingSystemMXBean;

/** *//**
 * 獲取系統信息的業務邏輯實現類.
 * @author amg * @version 1.0 Creation date: 2008-3-11 - 上午10:06:06
 */
public class MonitorServiceImpl implements IMonitorService {
    //可以設置長些，防止讀到運行此次系統檢查時的cpu占用率，就不準了
    private static final int CPUTIME = 5000;

    private static final int PERCENT = 100;

    private static final int FAULTLENGTH = 10;

    /** *//**
     * 獲得當前的監控對象.
     * @return 返回構造好的監控對象
     * @throws Exception
     * @author amg     * Creation date: 2008-4-25 - 上午10:45:08
     */
    public MonitorInfoBean getMonitorInfoBean() throws Exception {
        int kb = 1024;
       
        // 可使用內存
        long totalMemory = Runtime.getRuntime().totalMemory() / kb;
        // 剩余內存
        long freeMemory = Runtime.getRuntime().freeMemory() / kb;
        // 最大可使用內存
        long maxMemory = Runtime.getRuntime().maxMemory() / kb;

        OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory
                .getOperatingSystemMXBean();

        // 操作系統
        String osName = System.getProperty("os.name");
        // 總的物理內存
        long totalMemorySize = osmxb.getTotalPhysicalMemorySize() / kb;
        // 剩余的物理內存
        long freePhysicalMemorySize = osmxb.getFreePhysicalMemorySize() / kb;
        // 已使用的物理內存
        long usedMemory = (osmxb.getTotalPhysicalMemorySize() - osmxb
                .getFreePhysicalMemorySize())
                / kb;

        // 獲得線程總數
        ThreadGroup parentThread;
        for (parentThread = Thread.currentThread().getThreadGroup(); parentThread
                .getParent() != null; parentThread = parentThread.getParent())
            ;
        int totalThread = parentThread.activeCount();

        double cpuRatio = 0;
        if (osName.toLowerCase().startsWith("windows")) {
            cpuRatio = this.getCpuRatioForWindows();
        }
       
        // 構造返回對象
        MonitorInfoBean infoBean = new MonitorInfoBean();
        infoBean.setFreeMemory(freeMemory);
        infoBean.setFreePhysicalMemorySize(freePhysicalMemorySize);
        infoBean.setMaxMemory(maxMemory);
        infoBean.setOsName(osName);
        infoBean.setTotalMemory(totalMemory);
        infoBean.setTotalMemorySize(totalMemorySize);
        infoBean.setTotalThread(totalThread);
        infoBean.setUsedMemory(usedMemory);
        infoBean.setCpuRatio(cpuRatio);
        return infoBean;
    }

    /** *//**
     * 獲得CPU使用率.
     * @return 返回cpu使用率
     * @author amg     * Creation date: 2008-4-25 - 下午06:05:11
     */
    private double getCpuRatioForWindows() {
        try {
            String procCmd = System.getenv("windir")
                    + "//system32//wbem//wmic.exe process get Caption,CommandLine,"
                    + "KernelModeTime,ReadOperationCount,ThreadCount,UserModeTime,WriteOperationCount";
            // 取進程信息
            long[] c0 = readCpu(Runtime.getRuntime().exec(procCmd));
            Thread.sleep(CPUTIME);
            long[] c1 = readCpu(Runtime.getRuntime().exec(procCmd));
            if (c0 != null && c1 != null) {
                long idletime = c1[0] - c0[0];
                long busytime = c1[1] - c0[1];
                return Double.valueOf(
                        PERCENT * (busytime) / (busytime + idletime))
                        .doubleValue();
            } else {
                return 0.0;
            }
        } catch (Exception ex) {
            ex.printStackTrace();
            return 0.0;
        }
    }

    /** *//**
     * 讀取CPU信息.
     * @param proc
     * @return
     * @author amg     * Creation date: 2008-4-25 - 下午06:10:14
     */
    private long[] readCpu(final Process proc) {
        long[] retn = new long[2];
        try {
            proc.getOutputStream().close();
            InputStreamReader ir = new InputStreamReader(proc.getInputStream());
            LineNumberReader input = new LineNumberReader(ir);
            String line = input.readLine();
            if (line == null || line.length() < FAULTLENGTH) {
                return null;
            }
            int capidx = line.indexOf("Caption");
            int cmdidx = line.indexOf("CommandLine");
            int rocidx = line.indexOf("ReadOperationCount");
            int umtidx = line.indexOf("UserModeTime");
            int kmtidx = line.indexOf("KernelModeTime");
            int wocidx = line.indexOf("WriteOperationCount");
            long idletime = 0;
            long kneltime = 0;
            long usertime = 0;
            while ((line = input.readLine()) != null) {
                if (line.length() < wocidx) {
                    continue;
                }
                // 字段出現順序：Caption,CommandLine,KernelModeTime,ReadOperationCount,
                // ThreadCount,UserModeTime,WriteOperation
                String caption = Bytes.substring(line, capidx, cmdidx - 1)
                        .trim();
                String cmd = Bytes.substring(line, cmdidx, kmtidx - 1).trim();
                if (cmd.indexOf("wmic.exe") >= 0) {
                    continue;
                }
                // log.info("line="+line);
                if (caption.equals("System Idle Process")
                        || caption.equals("System")) {
                    idletime += Long.valueOf(
                            Bytes.substring(line, kmtidx, rocidx - 1).trim())
                            .longValue();
                    idletime += Long.valueOf(
                            Bytes.substring(line, umtidx, wocidx - 1).trim())
                            .longValue();
                    continue;
                }

                kneltime += Long.valueOf(
                        Bytes.substring(line, kmtidx, rocidx - 1).trim())
                        .longValue();
                usertime += Long.valueOf(
                        Bytes.substring(line, umtidx, wocidx - 1).trim())
                        .longValue();
            }
            retn[0] = idletime;
            retn[1] = kneltime + usertime;
            return retn;
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                proc.getInputStream().close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }
   
    /** *//**
     * 測試方法.
     * @param args
     * @throws Exception
     * @author amg     * Creation date: 2008-4-30 - 下午04:47:29
     */
    public static void main(String[] args) throws Exception {
        IMonitorService service = new MonitorServiceImpl();
        MonitorInfoBean monitorInfo = service.getMonitorInfoBean();
        System.out.println("cpu占有率=" + monitorInfo.getCpuRatio());
       
        System.out.println("可使用內存=" + monitorInfo.getTotalMemory());
        System.out.println("剩余內存=" + monitorInfo.getFreeMemory());
        System.out.println("最大可使用內存=" + monitorInfo.getMaxMemory());
       
        System.out.println("操作系統=" + monitorInfo.getOsName());
        System.out.println("總的物理內存=" + monitorInfo.getTotalMemorySize() + "kb");
        System.out.println("剩余的物理內存=" + monitorInfo.getFreeMemory() + "kb");
        System.out.println("已使用的物理內存=" + monitorInfo.getUsedMemory() + "kb");
        System.out.println("線程總數=" + monitorInfo.getTotalThread() + "kb");
    }
}
該實現類中需要用到一個自己編寫byte的工具類，該類的代碼如下所示：

Java代碼 
package  com.amgkaka.performance;  
  
/** */ /**  
 * byte操作類.  
 * @author amg * @version 1.0   
 * Creation date: 2008-4-30 - 下午04:57:23  
 */   
public   class  Bytes {  
    /** */ /**  
     * 由于String.subString對漢字處理存在問題（把一個漢字視為一個字節)，因此在  
     * 包含漢字的字符串時存在隱患，現調整如下：  
     * @param src 要截取的字符串  
     * @param start_idx 開始坐標（包括該坐標)  
     * @param end_idx   截止坐標（包括該坐標）  
     * @return  
     */   
    public   static  String substring(String src,  int  start_idx,  int  end_idx){  
        byte [] b = src.getBytes();  
        String tgt = "" ;  
        for ( int  i=start_idx; i<=end_idx; i++){  
            tgt +=(char )b[i];  
        }  
        return  tgt;  
    }  
}  
package com.amgkaka.performance;

/** *//**
 * byte操作類.
 * @author amg * @version 1.0
 * Creation date: 2008-4-30 - 下午04:57:23
 */
public class Bytes {
    /** *//**
     * 由于String.subString對漢字處理存在問題（把一個漢字視為一個字節)，因此在
     * 包含漢字的字符串時存在隱患，現調整如下：
     * @param src 要截取的字符串
     * @param start_idx 開始坐標（包括該坐標)
     * @param end_idx   截止坐標（包括該坐標）
     * @return
     */
    public static String substring(String src, int start_idx, int end_idx){
        byte[] b = src.getBytes();
        String tgt = "";
        for(int i=start_idx; i<=end_idx; i++){
            tgt +=(char)b[i];
        }
        return tgt;
    }
}
運行下MonitorBeanImpl類，讀者將會看到當前的內存、cpu利用率等信息。