Java Basic3(泛型、Muti-Processing、JMX、Stand Mbean、Dynamic Mbean)

一、泛型

Java1.5后支持。

注：C＋＋中有Template，是真正的泛型，但是会导致类膨胀；Java为伪泛型，编译时自动解析为原类型，也叫类型擦除。

1.Collection

2.Type erasing

-List<long>vs List<String>

3.? 通配符

二、Java Muti-Processing

1.Process

2.ProcessBuilder

3.Standard out/Error output/standard input

- stdin(0),stdout(1),stderr(2)

- Runntime

以下为通过线程调用系统ipconfig /all命令，获取当前主机相关信息

import java.io.InputStreamReader;
import java.io.LineNumberReader;public class RunCommand {public static void main(String[] args) throws Exception{for(int i=0; i<500; i++){run1("ipconfig");run2("ipconfig");System.out.println("i="+i);}}private static void run1(String command) throws Exception{ProcessBuilder pb = new ProcessBuilder(command, "/all");//, "myArg1", "myArg2");//Map<String, String> env = pb.environment();//env.put("VAR1", "myValue");//env.remove("OTHERVAR");//env.put("VAR2", env.get("VAR1") + "suffix");//pb.directory("myDir");Process p = pb.start();p.getErrorStream();InputStreamReader ir = new InputStreamReader(p.getInputStream());LineNumberReader input = new LineNumberReader(ir);String line;while ((line = input.readLine()) != null) {
//          System.out.println(line);if (line.indexOf("Host Name . . . . . . . . . . . . : ") != -1) {line = line.substring(line.indexOf(":"));System.out.println("Host Name:" + line);}else if (line.indexOf("Primary Dns Suffix  . . . . . . . : ") != -1) {line = line.substring(line.indexOf(":"));System.out.println("domain Name:" + line);}else if (line.indexOf("IPv4 Address. . . . . . . . . . . : ") != -1) {line = line.substring(line.indexOf(":"));System.out.println("IPv4 Address:" + line);}}ir.close();}private static void run2(String command) throws Exception{Process process=Runtime.getRuntime().exec(command);
//      InputStreamReader ir = new InputStreamReader(process.getInputStream());
//      LineNumberReader input = new LineNumberReader(ir);
//      String line;
//      while ((line = input.readLine()) != null) {
//          System.out.println(line);
//      }
//      ir.close();}}

三、JMX

1.Concept

https://www.ibm.com/developerworks/cn/java/j-lo-jse63/

Java Management Extension

Java SE 6新特性：JMX与系统管理

（1）控制台java命令jps可以查看当前运行的java进程

（2） sun.tools.jconsole.JConsole可以查看运行的JVM的各种信息

JConsole算是JMX的一个Client

（3）Java VisualVM监视工具

2.Mbean

采集CPU利用率、调集方法等等，调用信息。

java.lang Memory相当于一个Mbean，其有三大属性Attribute （可读写）、Operations（暴露给别人的一个方法，别人可以去调用它）、Notifications（通知，注册后，如有消息变化，则会主动推送到JMX Client）

四、Stand Mbean

1．Coding convention

－Attribute

－Operations

－Notifications

定义Mbean接口，类结尾必须是MBean；

凡成员变量全都必须有get，set方法：

以下类的作用为：暴露一个Mbean，有属性（C盘磁盘利用率），可读写，也有有参数返回值的操作（查看参数路径下的当前所有文件/目录名），写一个Client在里面进行操作Mbean：

public interface ConfigAlertParamMBean {public String getName();public void setName(String name);public double getDiskUsage();public void setDiskUsage(double diskUsage);public boolean changeAlertThreshold(int thresholdPercent);public void stopAndExit();public List<String> listFiles(String directory);   }

实现：

public class ConfigAlertParam implements ConfigAlertParamMBean{private String name; //this is an attributeprivate double diskUsage;private volatile int diskThreshold=80;private volatile boolean stop=false;@Overridepublic String getName() {return name;}@Overridepublic void setName(String name) {this.name=name;}@Overridepublic boolean changeAlertThreshold(int thresholdPercent) {this.diskThreshold=thresholdPercent;System.out.println("====set disk usage threshold:" + thresholdPercent );return true;}public boolean isExceedThreshold(int currentDiskUsage){return currentDiskUsage>=diskThreshold;}@Overridepublic void stopAndExit() {stop=true;}public boolean isStopped(){return stop;}@Overridepublic double getDiskUsage() {// TODO Auto-generated method stub
//      System.out.println("====set disk usage threshold:" + thresholdPercent );File[] roots = File.listRoots();for (File root : roots) {if (root.getPath().equals("C:\\")) {
//              System.out.println("Total space (bytes):" + root.getTotalSpace());
//              System.out.println("Usage space (bytes):" + root.getUsableSpace());
//              System.out.println((double)root.getUsableSpace()/root.getTotalSpace());diskUsage = (double)root.getUsableSpace()/root.getTotalSpace();}    }return diskUsage;}@Overridepublic void setDiskUsage(double diskUsage) {// TODO Auto-generated method stubthis.diskUsage = diskUsage;}@Overridepublic List<String> listFiles(String directory) {// TODO Auto-generated method stubFile dir = new File(directory);File[] files = dir.listFiles();System.out.println(files.length);    List<String> fileName = new ArrayList<String>(); ;for (File file : files) {            System.out.println(file.getAbsolutePath()); fileName.add(file.getAbsolutePath());}return fileName;}}

2．Register Mbean

－RemoteJMX service vi RMI

public class StartJMXServer {// JVM parameters:// -Dcom.sun.management.jmxremote.port=10000 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false//public static void main(String[] args){ConfigAlertParam bean1=new ConfigAlertParam();bean1.setName("disk usage threshold");MBeanServer mbeanServer=ManagementFactory.getPlatformMBeanServer();try{mbeanServer.registerMBean(bean1,ObjectName.getInstance("config:type=AlertParam"));}catch(Exception ex){ex.printStackTrace();}while(!bean1.isStopped()){int currentDiskUsage=new Random().nextInt(90);boolean exceeded = bean1.isExceedThreshold(currentDiskUsage);if(exceeded){System.out.println("disk usage has exceeded threshold:"+currentDiskUsage);System.out.println("The real disk usage is:" + bean1.getDiskUsage());}try{Thread.sleep(2000L);}catch(Exception ex){ex.printStackTrace();}}  System.out.println("jmx sever is stopped");}}

注意在该类Run Configurations的VM arguments中配置参数：
-Dcom.sun.management.jmxremote.port=10000
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false

3.How to access Mbean from other java process?

（1）可通过JConsole接到Mbean进行查看

（2）创建一个JMXClient客户端查看

public class JMXClient1 {public static void main(String[] args) throws Exception {Map<String, Object> jmxEnv=new HashMap<String, Object>();jmxEnv.put(Context.INITIAL_CONTEXT_FACTORY,"com.sun.jndi.rmi.registry.RegistryContextFactory");jmxEnv.put(RMIConnectorServer.JNDI_REBIND_ATTRIBUTE,"true");JMXServiceURL jmxServerUrl=new JMXServiceURL("service:jmx:rmi:///jndi/rmi://localhost:10000/jmxrmi");JMXConnector connector=JMXConnectorFactory.connect(jmxServerUrl,jmxEnv);MBeanServerConnection conn = connector.getMBeanServerConnection();Object result=conn.invoke(new ObjectName("config:type=AlertParam"), "changeAlertThreshold", new Object[]{ 50 }, new String[]{"int"});//int  java.lang.IntegerSystem.out.println(result);System.out.println(conn.getAttribute(new ObjectName("config:type=AlertParam"), "DiskUsage"));List<String> fileName = (List<String>) conn.invoke(new ObjectName("config:type=AlertParam"), "listFiles", new Object[]{ "C:workspace\\demo3\\src\\jmx" }, new String[]{"java.lang.String"});//int  java.lang.Integerfor (String file : fileName) {            System.out.println(file);   }
//      conn.getAttribute(hostName, attribute);}}

（3）Remote连接其他电脑的状况设置

五、Dynamic MBean

1.Use scenario

-We can’t change existing code to make some objects

2.Override methods