public class CeilAndFloor {
public static void main(String[] args) {
/*
q两个宝贝函数的主要d是截掉小C后的位数.
区别? floorL把数字变得越来越，而ceilL把数字变大?br /> 其实名字可以理解floor是地板，ceil是天花板?br /> */
System.out.println("==============Math.floor()==============");
System.out.println("Math.floor(99.1) = " + Math.floor(99.1));
System.out.println("Math.floor(-99.1) = " + Math.floor(-99.1));
System.out.println("Math.floor(99.9) = " + Math.floor(99.9));
System.out.println("Math.floor(99.9) = " + Math.floor(-99.9));
System.out.println("\n\n==============Math.ceil()==============");
System.out.println("Math.ceil(99.1) = " + Math.ceil(99.1));
System.out.println("Math.ceil(-99.1) = " + Math.ceil(-99.1));
System.out.println("Math.ceil(99.9) = " + Math.ceil(99.9));
System.out.println("Math.ceil(99.9) = " + Math.ceil(-99.9));
}
}
l果
==============Math.floor()==============
Math.floor(99.1) = 99.0
Math.floor(-99.1) = -100.0
Math.floor(99.9) = 99.0
Math.floor(99.9) = -100.0
==============Math.ceil()==============
Math.ceil(99.1) = 100.0
Math.ceil(-99.1) = -99.0
Math.ceil(99.9) = 100.0
Math.ceil(99.9) = -99.0
]]>
首先~写一个MonitorInfoBeanc，用来装蝲监控的一些信息，包括物理内存、剩余的物理内存、已使用的物理内存、内存用率{字D，该类的代码如下：
package com.amigo.performance;
/**
* 监视信息的JavaBeanc?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-4-25 - 上午10:37:00
*/
public class MonitorInfoBean {
/** 可用内? */
private long totalMemory;
/** 剩余内存. */
private long freeMemory;
/** 最大可使用内存. */
private long maxMemory;
/** 操作pȝ. */
private String osName;
/** ȝ物理内存. */
private long totalMemorySize;
/** 剩余的物理内? */
private long freePhysicalMemorySize;
/** 已用的物理内存. */
private long usedMemory;
/** U程L. */
private int totalThread;
/** cpu使用? */
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.amigo.performance;
/**
* 获取pȝ信息的业务逻辑cL?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-3-11 - 上午10:06:06
*/
public interface IMonitorService {
/**
* 获得当前的监控对?
* @return q回构造好的监控对?br /> * @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* Creation date: 2008-4-25 - 上午10:45:08
*/
public MonitorInfoBean getMonitorInfoBean() throws Exception;
}
package com.amigo.performance;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import sun.management.ManagementFactory;
import com.sun.management.OperatingSystemMXBean;
/**
* 获取pȝ信息的业务逻辑实现c?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0 Creation date: 2008-3-11 - 上午10:06:06
*/
public class MonitorServiceImpl implements IMonitorService {
private static final int CPUTIME = 30;
private static final int PERCENT = 100;
private static final int FAULTLENGTH = 10;
/**
* 获得当前的监控对?
* @return q回构造好的监控对?br /> * @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* Creation date: 2008-4-25 - 上午10:45:08
*/
public MonitorInfoBean getMonitorInfoBean() throws Exception {
int kb = 1024;
// 可用内?/span>
long totalMemory = Runtime.getRuntime().totalMemory() / kb;
// 剩余内存
long freeMemory = Runtime.getRuntime().freeMemory() / kb;
// 最大可使用内存
long maxMemory = Runtime.getRuntime().maxMemory() / kb;
OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory
.getOperatingSystemMXBean();
// 操作pȝ
String osName = System.getProperty("os.name");
// ȝ物理内存
long totalMemorySize = osmxb.getTotalPhysicalMemorySize() / kb;
// 剩余的物理内?/span>
long freePhysicalMemorySize = osmxb.getFreePhysicalMemorySize() / kb;
// 已用的物理内存
long usedMemory = (osmxb.getTotalPhysicalMemorySize() - osmxb
.getFreePhysicalMemorySize())
/ kb;
// 获得U程L
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();
}
// 构造返回对?/span>
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;
}
/**
* 获得CPU使用?
* @return q回cpu使用?br /> * @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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";
// 取进E信?/span>
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;
}
}
/**
* dCPU信息.
* @param proc
* @return
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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;
}
// 字段出现序QCaption,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;
}
/**
* 试Ҏ.
* @param args
* @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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?" + monitorInfo.getCpuRatio());
System.out.println("可用内?" + monitorInfo.getTotalMemory());
System.out.println("剩余内存=" + monitorInfo.getFreeMemory());
System.out.println("最大可使用内存=" + monitorInfo.getMaxMemory());
System.out.println("操作pȝ=" + monitorInfo.getOsName());
System.out.println("ȝ物理内存=" + monitorInfo.getTotalMemorySize() + "kb");
System.out.println("剩余的物理内?" + monitorInfo.getFreeMemory() + "kb");
System.out.println("已用的物理内存=" + monitorInfo.getUsedMemory() + "kb");
System.out.println("U程L=" + monitorInfo.getTotalThread() + "kb");
}
}
package com.amigo.performance;
/**
* byte操作c?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-4-30 - 下午04:57:23
*/
public class Bytes {
/**
* ׃String.subStringҎ字处理存在问题（把一个汉字视Z个字?Q因此在
* 包含汉字的字W串时存在隐患，现调整如下：
* @param src 要截取的字符?br /> * @param start_idx 开始坐标（包括该坐?
* @param end_idx 截止坐标Q包括该坐标Q?br /> * @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.amigo.performance;
/**
* 监视信息的JavaBeanc?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-4-25 - 上午10:37:00
*/
public class MonitorInfoBean {
/** 可用内? */
private long totalMemory;
/** 剩余内存. */
private long freeMemory;
/** 最大可使用内存. */
private long maxMemory;
/** 操作pȝ. */
private String osName;
/** ȝ物理内存. */
private long totalMemorySize;
/** 剩余的物理内? */
private long freePhysicalMemorySize;
/** 已用的物理内存. */
private long usedMemory;
/** U程L. */
private int totalThread;
/** cpu使用? */
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;
}
}
接着~写一个获得当前的监控信息的接口，该类的代码如下所C：
package com.amigo.performance;
/**
* 获取pȝ信息的业务逻辑cL?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-3-11 - 上午10:06:06
*/
public interface IMonitorService {
/**
* 获得当前的监控对?
* @return q回构造好的监控对?br /> * @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* Creation date: 2008-4-25 - 上午10:45:08
*/
public MonitorInfoBean getMonitorInfoBean() throws Exception;
}
该类的实现类MonitorServiceImpl如下所C：
package com.amigo.performance;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import sun.management.ManagementFactory;
import com.sun.management.OperatingSystemMXBean;
/**
* 获取pȝ信息的业务逻辑实现c?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0 Creation date: 2008-3-11 - 上午10:06:06
*/
public class MonitorServiceImpl implements IMonitorService {
private static final int CPUTIME = 30;
private static final int PERCENT = 100;
private static final int FAULTLENGTH = 10;
/**
* 获得当前的监控对?
* @return q回构造好的监控对?br /> * @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* Creation date: 2008-4-25 - 上午10:45:08
*/
public MonitorInfoBean getMonitorInfoBean() throws Exception {
int kb = 1024;
// 可用内?/span>
long totalMemory = Runtime.getRuntime().totalMemory() / kb;
// 剩余内存
long freeMemory = Runtime.getRuntime().freeMemory() / kb;
// 最大可使用内存
long maxMemory = Runtime.getRuntime().maxMemory() / kb;
OperatingSystemMXBean osmxb = (OperatingSystemMXBean) ManagementFactory
.getOperatingSystemMXBean();
// 操作pȝ
String osName = System.getProperty("os.name");
// ȝ物理内存
long totalMemorySize = osmxb.getTotalPhysicalMemorySize() / kb;
// 剩余的物理内?/span>
long freePhysicalMemorySize = osmxb.getFreePhysicalMemorySize() / kb;
// 已用的物理内存
long usedMemory = (osmxb.getTotalPhysicalMemorySize() - osmxb
.getFreePhysicalMemorySize())
/ kb;
// 获得U程L
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();
}
// 构造返回对?/span>
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;
}
/**
* 获得CPU使用?
* @return q回cpu使用?br /> * @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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";
// 取进E信?/span>
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;
}
}
/**
* dCPU信息.
* @param proc
* @return
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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;
}
// 字段出现序QCaption,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;
}
/**
* 试Ҏ.
* @param args
* @throws Exception
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* 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?" + monitorInfo.getCpuRatio());
System.out.println("可用内?" + monitorInfo.getTotalMemory());
System.out.println("剩余内存=" + monitorInfo.getFreeMemory());
System.out.println("最大可使用内存=" + monitorInfo.getMaxMemory());
System.out.println("操作pȝ=" + monitorInfo.getOsName());
System.out.println("ȝ物理内存=" + monitorInfo.getTotalMemorySize() + "kb");
System.out.println("剩余的物理内?" + monitorInfo.getFreeMemory() + "kb");
System.out.println("已用的物理内存=" + monitorInfo.getUsedMemory() + "kb");
System.out.println("U程L=" + monitorInfo.getTotalThread() + "kb");
}
}
该实现类中需要用C个自q写byte的工LQ该cȝ代码如下所C：
package com.amigo.performance;
/**
* byte操作c?
* @author <a href="mailto:xiexingxing1121@126.com">AmigoXie</a>
* @version 1.0
* Creation date: 2008-4-30 - 下午04:57:23
*/
public class Bytes {
/**
* ׃String.subStringҎ字处理存在问题（把一个汉字视Z个字?Q因此在
* 包含汉字的字W串时存在隐患，现调整如下：
* @param src 要截取的字符?br /> * @param start_idx 开始坐标（包括该坐?
* @param end_idx 截止坐标Q包括该坐标Q?br /> * @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;
}
}
q行下MonitorBeanImplc，读者将会看到当前的内存、cpu利用率等信息?/span>
]]>
]]>
ListResourceBundle ?nbsp;ResourceBundle 的一个抽象类Q用于管理方便而又易于使用的列表中的语a环境资源。有兌源包的常规信息，请参?nbsp;ResourceBundle?br /> 子类必须重写 getContents q提供一个数l，其中数组中的每个w是一个对象对。每对的W一个元素是键，该键必须是一?nbsp;StringQƈ且第二个元素是和该键相关联的倹{?br /> 下面?/span>CZ昄了具有基本名U?"MyResources" 的资源包pd的两个成员?MyResources" 是资源包pd的默认成员，"MyResources_fr" ?French 成员。这些成员是ZListResourceBundleQ一个相关的CZ昄了如何把一个资源包d到基于属性文件的此系列）。此CZ中的键Ş式ؓ "s1" {。实际的键完全取决于您的选择Q只要它们和E序中用于从资源包中获取对象的键相同。键区分大小写?br /> public class MyResources extends ListResourceBundle {
protected Object[][] getContents() {
return new Object[][] = {
// LOCALIZE THIS
{"s1", "The disk \"{1}\" contains {0}."}, // MessageFormat pattern
{"s2", "1"}, // location of {0} in pattern
{"s3", "My Disk"}, // sample disk name
{"s4", "no files"}, // first ChoiceFormat choice
{"s5", "one file"}, // second ChoiceFormat choice
{"s6", "{0,number} files"}, // third ChoiceFormat choice
{"s7", "3 Mar 96"}, // sample date
{"s8", new Dimension(1,5)} // real object, not just string
// END OF MATERIAL TO LOCALIZE
};
}
}
public class MyResources_fr extends ListResourceBundle {
protected Object[][] getContents() {
return new Object[][] = {
// LOCALIZE THIS
{"s1", "Le disque \"{1}\" {0}."}, // MessageFormat pattern
{"s2", "1"}, // location of {0} in pattern
{"s3", "Mon disque"}, // sample disk name
{"s4", "ne contient pas de fichiers"}, // first ChoiceFormat choice
{"s5", "contient un fichier"}, // second ChoiceFormat choice
{"s6", "contient {0,number} fichiers"}, // third ChoiceFormat choice
{"s7", "3 mars 1996"}, // sample date
{"s8", new Dimension(1,3)} // real object, not just string
// END OF MATERIAL TO LOCALIZE
};
}
}
]]>
What is ClassLoader?
与普通程序不同的是，JavaE序Qclass文gQƈ不是本地的可执行E序。当q行JavaE序Ӟ首先q行JVMQJava虚拟机）Q然后再把Java class加蝲到JVM里头q行Q负责加载Java class的这部分叫做Class Loader?/span>
JVM本n包含了一个ClassLoaderUCؓBootstrap ClassLoaderQ和JVM一PBootstrapClassLoader是用本地代码实现的，它负责加载核心JavaClassQ即所有java.*开头的c）。另外JVMq会提供两个ClassLoaderQ它们都是用Java语言~写的，由BootstrapClassLoader加蝲Q其中Extension ClassLoader负责加蝲扩展的JavaclassQ例如所有javax.*开头的cd存放在JRE的ext目录下的c）QApplicationClassLoader负责加蝲应用E序自n的类?/span> 当运行一个程序的时候，JVM启动Q运行bootstrapclassloaderQ该ClassLoader加蝲java核心APIQExtClassLoader和AppClassLoader也在此时被加载）Q然后调用ExtClassLoader加蝲扩展APIQ最后AppClassLoader加蝲CLASSPATH目录下定义的ClassQ这是一个程序最基本的加载流E?/span> ? 学ClassLoader看OSGI
When to load the class?
什么时候JVM会用ClassLoader加蝲一个类呢？当你使用javaL行一个类QJVM使用ApplicationClassLoader加蝲q个c；然后如果cA引用了类BQ不是直接引用q是用Class.forName()引用QJVM׃扑ֈ加蝲cA的ClassLoaderQƈ用这个ClassLoader来加载类B。JVM按照q行时的有效执行语句Q来军_是否需要装载新c，从而装载尽可能的c，q一点和~译cL不相同的?/span> Why use your own ClassLoader? gJVM自n的ClassLoader已经_了，Z么我们还需要创qClassLoader呢？ 因ؓJVM自带的ClassLoader只是懂得从本地文件系l加载标准的java class文gQ如果编写你自己的ClassLoaderQ你可以做到Q?/span> 1Q在执行非置信代码之前，自动验证数字{ 2Q动态地创徏W合用户特定需要的定制化构建类 3Q从特定的场所取得java classQ例如数据库?/span> 4) {等 事实上当使用Applet的时候，qC特定的ClassLoaderQ因旉要从|络上加载java classQƈ且要查相关的安全信息?/span> 目前的应用服务器大都使用了ClassLoader技术，即你不需要创qClassLoaderQ了解其原理也有助于更好地部|自q应用?br />
ClassLoader Tree & Delegation Model
当你军_创徏你自qClassLoaderӞ需要承java.lang.ClassLoader或者它的子cR在实例化每个ClassLoader对象Ӟ需要指定一个父对象Q如果没有指定的话，pȝ自动指定ClassLoader.getSystemClassLoader()为父对象?/span> 所以当创徏自己的Class LoaderӞ只需要重载findClass()q个Ҏ?br />Unloading? Reloading?
当一个javaclass被加载到JVM之后Q它有没有可能被卸蝲呢？我们知道Win32有FreeLibrary()函数QPosix有dlclose()函数可以被调用来卸蝲指定的动态连接库Q但是Javaq没有提供一个UnloadClass()的方法来卸蝲指定的类?/span> 在Java中，java class的卸载仅仅是一U对pȝ的优化，有助于减应用对内存的占用。既然是一U优化方法，那么完全是JVM自行军_如何实现Q对Java开发h员来说是完全透明的?/span> 在什么时候一个java class/interface会被卸蝲呢？Sun公司的原话是q么说的Q?class or interfacemay be unloaded if and only if its class loader is unreachable. Classesloaded by the bootstrap loader may not be unloaded." 事实上我们关心的不是如何卸蝲cȝQ我们关心的是如何更新已l被加蝲了的cM而更新应用的功能。JSP则是一个非常典型的例子Q如果一个JSP文g被更改了Q应用服务器则需要把更改后的JSP重新~译Q然后加载新生成的类来响应后l的h?/span> 其实一个已l加载的cL无法被更新的Q如果你试图用同一个ClassLoader再次加蝲同一个类Q就会得到异常（java.lang.LinkageError: duplicate classdefinitionQ，我们只能够重新创Z个新的ClassLoader实例来再ơ加载新cR至于原来已l加载的c，开发h员不必去它Q因为它可能q有实例正在被用，只要相关的实例都被内存回收了Q那么JVM׃在适当的时候把不会再用的cd载?/span> 使用U程上下文类加蝲? 可以在执行线E中, 抛弃双亲委派加蝲链模? 使用U程上下文里的类加蝲器加载类. 典型的例子有, 通过U程上下文来加蝲W三方库jndi实现, 而不依赖于双亲委z? 大部分java app服务?jboss, tomcat..)也是采用contextClassLoader来处理web服务?/span> 当然, 好东襉K有利? 使用U程上下文加载类, 也要注意, 保证多根需要通信的线E间的类加蝲器应该是同一? 防止因ؓ不同的类加蝲? Dcd转换异常(ClassCastException). 参考资料及囄来源——Understanding J2EE Application Server Class Loading Architectures
ClassLoader Tree & Delegation Model
当你军_创徏你自qClassLoaderӞ需要承java.lang.ClassLoader或者它的子cR在实例化每个ClassLoader对象Ӟ需要指定一个父对象Q如果没有指定的话，pȝ自动指定ClassLoader.getSystemClassLoader()为父对象?/span> 所以当创徏自己的Class LoaderӞ只需要重载findClass()q个Ҏ?br />Unloading? Reloading?
当一个javaclass被加载到JVM之后Q它有没有可能被卸蝲呢？我们知道Win32有FreeLibrary()函数QPosix有dlclose()函数可以被调用来卸蝲指定的动态连接库Q但是Javaq没有提供一个UnloadClass()的方法来卸蝲指定的类?/span> 在Java中，java class的卸载仅仅是一U对pȝ的优化，有助于减应用对内存的占用。既然是一U优化方法，那么完全是JVM自行军_如何实现Q对Java开发h员来说是完全透明的?/span> 在什么时候一个java class/interface会被卸蝲呢？Sun公司的原话是q么说的Q?class or interfacemay be unloaded if and only if its class loader is unreachable. Classesloaded by the bootstrap loader may not be unloaded." 事实上我们关心的不是如何卸蝲cȝQ我们关心的是如何更新已l被加蝲了的cM而更新应用的功能。JSP则是一个非常典型的例子Q如果一个JSP文g被更改了Q应用服务器则需要把更改后的JSP重新~译Q然后加载新生成的类来响应后l的h?/span> 其实一个已l加载的cL无法被更新的Q如果你试图用同一个ClassLoader再次加蝲同一个类Q就会得到异常（java.lang.LinkageError: duplicate classdefinitionQ，我们只能够重新创Z个新的ClassLoader实例来再ơ加载新cR至于原来已l加载的c，开发h员不必去它Q因为它可能q有实例正在被用，只要相关的实例都被内存回收了Q那么JVM׃在适当的时候把不会再用的cd载?/span> 使用U程上下文类加蝲? 可以在执行线E中, 抛弃双亲委派加蝲链模? 使用U程上下文里的类加蝲器加载类. 典型的例子有, 通过U程上下文来加蝲W三方库jndi实现, 而不依赖于双亲委z? 大部分java app服务?jboss, tomcat..)也是采用contextClassLoader来处理web服务?/span> 当然, 好东襉K有利? 使用U程上下文加载类, 也要注意, 保证多根需要通信的线E间的类加蝲器应该是同一? 防止因ؓ不同的类加蝲? Dcd转换异常(ClassCastException). 参考资料及囄来源——Understanding J2EE Application Server Class Loading Architectures
Unloading? Reloading?
当一个javaclass被加载到JVM之后Q它有没有可能被卸蝲呢？我们知道Win32有FreeLibrary()函数QPosix有dlclose()函数可以被调用来卸蝲指定的动态连接库Q但是Javaq没有提供一个UnloadClass()的方法来卸蝲指定的类?/span> 在Java中，java class的卸载仅仅是一U对pȝ的优化，有助于减应用对内存的占用。既然是一U优化方法，那么完全是JVM自行军_如何实现Q对Java开发h员来说是完全透明的?/span> 在什么时候一个java class/interface会被卸蝲呢？Sun公司的原话是q么说的Q?class or interfacemay be unloaded if and only if its class loader is unreachable. Classesloaded by the bootstrap loader may not be unloaded." 事实上我们关心的不是如何卸蝲cȝQ我们关心的是如何更新已l被加蝲了的cM而更新应用的功能。JSP则是一个非常典型的例子Q如果一个JSP文g被更改了Q应用服务器则需要把更改后的JSP重新~译Q然后加载新生成的类来响应后l的h?/span> 其实一个已l加载的cL无法被更新的Q如果你试图用同一个ClassLoader再次加蝲同一个类Q就会得到异常（java.lang.LinkageError: duplicate classdefinitionQ，我们只能够重新创Z个新的ClassLoader实例来再ơ加载新cR至于原来已l加载的c，开发h员不必去它Q因为它可能q有实例正在被用，只要相关的实例都被内存回收了Q那么JVM׃在适当的时候把不会再用的cd载?/span> 使用U程上下文类加蝲? 可以在执行线E中, 抛弃双亲委派加蝲链模? 使用U程上下文里的类加蝲器加载类. 典型的例子有, 通过U程上下文来加蝲W三方库jndi实现, 而不依赖于双亲委z? 大部分java app服务?jboss, tomcat..)也是采用contextClassLoader来处理web服务?/span> 当然, 好东襉K有利? 使用U程上下文加载类, 也要注意, 保证多根需要通信的线E间的类加蝲器应该是同一? 防止因ؓ不同的类加蝲? Dcd转换异常(ClassCastException). 参考资料及囄来源——Understanding J2EE Application Server Class Loading Architectures
]]>