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Selector是用来获取注册在其中的channel的相关事件的发生Q也是acceptQread和write。selector中有3个key set?
key setQ包含代表所有在其中注册的channelQ可以通过selector.keys()得到?
selected-key setQ包含所有被到有关注的操作已经qA的keyQ通过selector.selectedKeys得到?
cancelled-key setQ包含所有已l被cancelQ但是还没有channelq没有deregister的keyQ这个集合是不能直接被访问的?br>
key通过调用channel的registerҎ被加入到key set中。被取消的key在select的时候会被从相应的key set中移除?br>
key set自n是不可以直接q行修改的? 无论是通过调用channel的closeҎq是调用key的cancelҎQkey都会被放|到canceled-key set中。取消的key会将其channel在下一ơselect时将注册撤销Q同时将key从所有的key set中移除?
key在执行select操作时被加入到selected-key set中。在selected-key set中的key可以通过调用iterator的removeҎQ将其从selected-key set中移除，不能通过其他的办法将其从selected-key set中移除?br>
通过selector?个方法selectQ阻塞选择Q直到有兛_的事件发生时退出阻塞）QselectNowQ不d选择Q，select(long)Q指定超旉择Q超时到达或者有兛_事g发生旉出阻塞）Q来获取兛_事g的发生。其执行步骤分ؓ以下3步：
1、将存在于canceled-key set中的key从所有的key set中移除，撤销注册的channelQ清Icanceled-key set?
2、地层操作系l检查是否有兛_的事件发生，当有兛_的事件发生时Q首先检查channel的key是否已经存在于selected-key set中，如果不存在，则将其加入到selected-key set中去Q同时修改key的ready-operation set来表明当前ready的操作，而以前存在于ready-operation set中的信息会被删除。如果对应的key已经存在于selected-key set中，q直接修改其ready-operation set来表明当前ready的操作，删除原来ready-operation set中的信息?
3、如果在W二步中有加入到canceled-key set中的keyQ在q一步会执行W一步的操作?
selector自n是线E安全的Q而他的key set却不是。在一ơ选择发生的过E中Q对于key的关心事件的修改要等C一ơselect的时候才会生效? 另外Qkey和其代表的channel有可能在M时候被cancel和close。因此存在于key set中的keyq不代表其key是有效的Q也不代表其channel是open的。如果key有可能被其他的线E取消或关闭channelQ程序必d 心的同步查这些条件?
d了的select可以通过调用selector的wakeupҎ来唤醒?img src ="http://www.aygfsteel.com/Tower/aggbug/3809.html" width = "1" height = "1" />
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最q同样在目中需要去解决一个异构问题，׃旉的紧q，以及先天的运行环境（两个部分是运行在同一台机器上的）。考虑C使用JNIQ结果表明JNI是完全可以胜ȝ前的角色的。以前没有了解过JNIQL以ؓ它这不好那不好，用了用，表现q不错，而且实现h非常之简单?BR>
整个实现q程可以分ؓ五步来完成：
1Q写一个声明了native的Java文gQ?/FONT>
package example;
public class TestJNI 
{
static {
System.loadLibrary("test");
} public native String getNameCPP();
}2) 使用javah产生对应的CPP头文Ӟ
命oQjavah -classpath <path> -jni example.TestJNI -d <out_dir>
生成的头文gexample_TestJNI.h如下Q?BR>
/**//* DO NOT EDIT THIS FILE - it is machine generated */#include <jni.h>/**//* Header for class example_TestJNI */#ifndef _Included_example_TestJNI#define _Included_example_TestJNI#ifdef __cplusplusextern "C" {#endif/**//* * Class: example_TestJNI * Method: getNameForCPP * Signature: ()Ljava/lang/String; */JNIEXPORT jstring JNICALL Java_example_TestJNI_getNameForCPP (JNIEnv *, jobject);#ifdef __cplusplus}#endif#endif3Q实现对应的CPP代码Q?BR>
#include "example_TestJNI.h"#include <string>JNIEXPORT jstring JNICALL Java_example_TestJNI_getNameForCPP (JNIEnv * env, jobject){ //TODO 可以在此调用其他的代?/SPAN> std::string strName = "Tower"; return env->NewStringUTF(strName.c_str());}4) ~译CPP代码
命oQg++ -o libtest.so -shared -I<include_path> -I<java_home>/include -I<java_home>/include/linux example_TestJNI.cpp
5Q执?BR>
package example;public class Test { public static void main(String[] args) { TestJNI test = new TestJNI(); System.out.println("Hello " + test.getNameForCPP()); }}export LD_EXPORT_PATH=<so_path>
java -cp <path> -Djava.library.path=<so_path> example.Test
输出QHello Tower
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Hibernate的承映包含了三种不同的策略：
- 每簇cM用一个表Q?
- 每个子类一个表Q?
- 每个具体内一个表Q有限制Q?BR>
class Animal { private String identifier; private String name; private String category; // setter and getter}文g名：Dog.java
class Dog extends Animal { private String // setter and getter}文g名：Cat.java
class Cat extends Animal { private String // setter and getter}- 每簇cM用一个表
<class name="Animal" table="TB_ANIMAL"> <id name="identifier" type="string" column="IDENTIFIER"> <generator class="uuid.hex"/> </id> <discriminator column="ANIMAL_TYPE" type="string"/> <property name="name" column="NAME" type="string"/> <subclass name="Dog" discriminator-value="DOG"> </subclass> <subclass name="Cat" discriminator-value="CAT"> </subclass> </class>- 每个子类一个表
<class name="Animal" table="ANIMAL"> <id name="identifier" column="IDENTIFIER" type="string"> <generator class="uuid.hex"/> </id> <property > </class> 文g名：Dog.hbm.xml <joined-subclass name="Dog" table="DOG" extends="Animal"> <key column="DOG_ID"/> </joined-subclass> 文g名：Cat.hbm.xml <joined-subclass name="Cat" table="CAT" extends="Cat"> <key column="CAT_ID"/> </joined-subclass>每个子类一个表的策略实际上一Uone-to-one的映?BR>
- 每个具体内一个表Q有限制Q?/B>
<class name="Dog" table="DOG"> <id name="identifier" column="IDENTIFIER" type="string"> <generator class="uuid.hex"/> </id> <property name="name" column="NAME" type="string"/> </class> 文g名：Cat.hbm.xml <class name="Cat" table="CAT"> <id name="identifier" column="IDENTIFIER" type="string"> <generator class="uuid.hex"/> </id> <property name="name" column="NAME" type="string"/> </class>]]>
对于如何产生和注册MBeansQmx4j提供了一个相当方便的工具Qؓ什么说相当方便Q是因ؓ它真的实在是太方便了。通过写一个xml配置文g可以完成所有的工作。比起M-LET实是强了不。下面就是一个在MBean Server产生注册一个NamingService、JMXConnectorServer和一个自写的MBean的配|文件?BR>
<?xml version="1.0" encoding="UTF-8"?><configuration port="9999"> <startup> <create classname="mx4j.tools.naming.NamingService" objectname="naming:type=rmiregistry"> <arg type="int">1099</arg> </create> <call operation="start" objectname="naming:type=rmiregistry" /> <object objectid="rmi"> <call classname="javax.management.remote.JMXConnectorServerFactory" method="newJMXConnectorServer"> <arg type="javax.management.remote.JMXServiceURL"> <new classname="javax.management.remote.JMXServiceURL"> <arg type="string">service:jmx:rmi://localhost/jndi/rmi://localhost:1099/jmx</arg> </new> </arg> <arg type="java.util.Map" /> <arg type="javax.management.MBeanServer" /> </call> </object> <register objectname="connectors:type=rmi,protocol=jrmp"> <arg type="object" refobjectid="rmi" /> </register> <call method="start" refobjectid="rmi" /> <create classname="nsmp.examples.mbeans.rmi.MyRemoteServiceObject" objectname="services:type=my-remote" /> </startup> <shutdown> <call operation="stop" objectname="services:type=my-remote" /> <call method="stop" refobjectid="rmi" /> <call operation="stop" objectname="naming:type=rmiregistry" /> <unregister objectname="services:type=my-remote"/> <unregister objectname="connectors:type=rmi,protocol=jrmp" /> <unregister objectname="naming:type=rmiregistry" /> </shutdown></configuration> java代码Q?BR>
package nsmp.agent;import java.io.BufferedReader;import java.io.FileReader;import java.io.Reader;import java.net.Socket;import javax.management.MBeanServer;import javax.management.MBeanServerFactory;import javax.management.ObjectName;import mx4j.tools.config.ConfigurationLoader;import nsmp.util.NsmpGlobals;/**//** * @version 1.0 * @author tower * * TODO write the comment of this type */public class NsmpServer { public void startup() throws Exception { MBeanServer server = MBeanServerFactory.newMBeanServer(); ConfigurationLoader loader = new ConfigurationLoader(); server.registerMBean(loader, ObjectName.getInstance("config:service=loader")); Reader reader = new BufferedReader(new FileReader(NsmpGlobals.NSMP_HOME + "/conf/config.xml")); loader.startup(reader); reader.close(); System.out.println("Start the nsmp server successfully!"); } public void shutdown() throws Exception { String shutdownCommand = "shutdown"; Socket socket = new Socket("127.0.0.1", 9999); socket.getOutputStream().write(shutdownCommand.getBytes()); socket.close(); }}startupҎ调用配置文g的startup部分完成创徏和注册，shutdownҎ调用配置文g的shutdown部分释放相应的资源。通过调用 startupҎ可以v动MBeanServer提供服务了。对于shutdown开始搞了我半天startup?ConfigurationLoader都没有创Z个侦听端口来接收shutdown命oQ看了看mx4j的源码发?ConfigurationLoader也没有发C么特D地斏V捉摸半天终于发C自己放了一个愚W的错误Qeclipse是用普通用h限开的，没有办法创徏侦听Q改成root后一切ok?BR>
接下随便写了一个JMXConnectorQ代码：
/**//* * Copyright (C) The MX4J Contributors. * All rights reserved. * * This software is distributed under the terms of the MX4J License version 1.0. * See the terms of the MX4J License in the documentation provided with this software. */package nsmp.examples.mbeans.rmi;import java.util.Map;import javax.management.MBeanInfo;import javax.management.MBeanOperationInfo;import javax.management.MBeanServerConnection;import javax.management.ObjectName;import javax.management.remote.JMXConnector;import javax.management.remote.JMXConnectorFactory;import javax.management.remote.JMXServiceURL;/**//** * @version $Revision: 1.3 $ */public class Client{ public static void main(String[] args) throws Exception { JMXServiceURL address = new JMXServiceURL("service:jmx:rmi://localhost/jndi/rmi://localhost:1099/jmx"); Map creationEnv = null; JMXConnector connector = JMXConnectorFactory.newJMXConnector(address, creationEnv); Map connectionEnv = null; connector.connect(connectionEnv); MBeanServerConnection serverConnection = connector.getMBeanServerConnection(); ObjectName name = ObjectName.getInstance("services:type=my-remote"); MBeanInfo mbInfo = serverConnection.getMBeanInfo(name); MBeanOperationInfo[] operationInfo = mbInfo.getOperations(); for (int i = 0; i < operationInfo.length; i++) { System.out.println(operationInfo[i].getName()); } serverConnection.invoke(name, "sayHello", new Object[] {"Tower He"}, new String[] {"java.lang.String"}); }}JMXConnector是通过获取一个MBeanServerConnection来实现远E调用的Q运行了一下一切顺利通过?BR>
下蝲Q?A href="http://www.aygfsteel.com/Files/Tower/MX4JExample.rar">MX4JExample.rar
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