Java Code Snippets

2014-11-07

Byte array to hex string

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public static String toHexString(byte[] array) {
    return javax.xml.bind.DatatypeConverter.printHexBinary(array);
}

Code in comments

/**
 * <PRE>
 * insert code as you would anywhere else
 * </PRE>
 */

An Example from a java.awt.Event method javadoc:

/**
 * <PRE>
 *    int onmask = SHIFT_DOWN_MASK | BUTTON1_DOWN_MASK;
 *    int offmask = CTRL_DOWN_MASK;
 *    if ((event.getModifiersEx() & (onmask | offmask)) == onmask) {
 *        ...
 *    }
 * </PRE>
 */

Get field descriptions (names)

public static <T, K> Map<K, String> getFieldDescriptions(Class<T> clazz) {
	Map<K, String> map = new HashMap<K,String>();
	for (Field f : clazz.getDeclaredFields()) {
		int mod = f.getModifiers();
		if (Modifier.isPublic(mod) && Modifier.isFinal(mod) && Modifier.isStatic(mod)) {
			try {
				@SuppressWarnings("unchecked")
				K fld = (K) f.get(null);
				
				Integer st = null;
				if (fld instanceof Integer) {
					st = (Integer) fld;
				} else if (fld instanceof Short) {
					st = (int) (short) (Short) fld;
				}
				map.put(fld, String.format("0x%04X, %s", st&0xFFFFFFFF, f.getName()));
			} catch (Exception ex) {
				/* ignore */
			}
		}
	}
	
	return map;
}

more >>

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Tomcat Tips

2014-11-03

Some tips for Tomcat7.

Move the constant lib as external libs:

Step 1: Copy the lib to somewhere else, e.g. ${catalina.home}/anyfish-lib
Step 2: Eclipse: Properties for app > Deployment Assembly > Remove ‘Maven Dependencies’

Step 3: Add following config in /conf/context.xml:

1	<Loader className="org.apache.catalina.loader.VirtualWebappLoader" virtualClasspath="${catalina.home}/anyfish-lib/*.jar" />

So the final packaged .war file size is reduced dramatically!

To achive Step 2 in maven, edit the pom.xml file:

<properties>
	<maven.build.timestamp.format>yyyyMMddHHmm</maven.build.timestamp.format>
</properties>
<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-war-plugin</artifactId>
			<version>2.4</version>
			<configuration>
				<warName>${project.artifactId}##${maven.build.timestamp}</warName>
				<packagingExcludes>%regex[WEB-INF/lib/(?!mylib-1.0.0-SNAPSHOT).*.jar]</packagingExcludes>
			</configuration>
		</plugin>
	</plugins>
</build>

Note the <packagingExcludes>%regex[WEB-INF/lib/(?!mylib-1.0.0-SNAPSHOT).*.jar]</packagingExcludes> config above (Don’t package the common spring, logging libaries etc into .war file; keep only mylib.jar).

Deploy new version w/o shutting down tomcat

To deploy a new version of webapp without shutting down tomcat, use parallel deployment in tomcat7, refer to tomcat parallel deploy.

Note the <warName>${project.artifactId}##${maven.build.timestamp}</warName> config above.

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Maven Tips

2014-10-11

使用国内的镜像地址

mavn 中央库默认的下载地址在国外，下载速度不稳定。开源中国做了国内镜像，参考其帮助文档配置其为中央库：

备份 Maven 的安装目录下的 conf/settings.xml 文件，再编辑它：

<mirrors>
	<!-- http://maven.oschina.net/static/help.html -->
	<mirror>
		<id>nexus-osc</id>
		<mirrorOf>*</mirrorOf>
		<name>Nexus OSC</name>
		<url>http://maven.oschina.net/content/groups/public/</url>
	</mirror>
</mirrors>
<profiles>
	<!-- http://maven.oschina.net/static/help.html -->
	<profile>
		<id>jdk-1.4</id>
		<activation><jdk>1.4</jdk></activation>
		<repositories>
			<repository>
				<id>nexus</id>
				<name> local private nexus</name>
				<url>http://maven.oschina.net/content/groups/public</url>
				<releases><enabled>true</enabled></releases>
				<snapshots><enabled>false</enabled></snapshots>
			</repository>
		</repositories>
		<pluginRepositories>
			<pluginRepository>
				<id>nexus</id>
				<name>local private enxus</name>
				<url>http://maven.oschina.net/content/groups/public</url>
				<releases><enabled>true</enabled></releases>
				<snapshots><enabled>false</enabled></snapshots>
			</pluginRepository>
		</pluginRepositories>
	</profile>
</profiles>

自定义生成 war 包的内容和文件名

<properties>
	<maven.build.timestamp.format>yyyyMMddHHmm</maven.build.timestamp.format>
</properties>
<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-war-plugin</artifactId>
			<version>2.4</version>
			<configuration>
				<warName>${project.artifactId}##${maven.build.timestamp}</warName>
				<packagingExcludes>%regex[WEB-INF/lib/(?!mylib-1.0.0-SNAPSHOT).*.jar]</packagingExcludes>
			</configuration>
		</plugin>
	</plugins>
</build>

以上配置，

在生成的 war 包名字的后面加上打包时间；
不将公共的 spring, json 的相关 jar 包打到最终 war 包中，只保留自己的、经常会变化的 mylib-1.0.0-SNAPSHOT，参见Tomcat Tips。

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Tomcat 并行部署

2014-09-22

背景知识： tomcat的并行部署

部署新版本时，一般要先停掉旧的应用，复制新应用后，再启动tomcat，这就造成中间有一段时间 tomcat 是无法对外服务的。

从Tomcat 7.0.23+开始，可以在不关闭 Tomcat 的情况下同时部署相同context path的多个不同版本的web应用。war包的命名格式形如context.war, context##2.war,context##3.war。

当用户访问 http://[url]/context 时，规则如下:

如果当前请求没有session信息，则使用最新的war应用版本
如果当前请求有session，使用session对应的war应用版本
如果当前请求有session信息，却找不到相应的war应用版本，则使用最新的war应用版本（context##3.war）

实现并行部署

pom.xml 中配置生成的 war 包加时间戳：

<properties>
	<maven.build.timestamp.format>yyyyMMddHHmm</maven.build.timestamp.format>
</properties>
<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-war-plugin</artifactId>
			<version>2.4</version>
			<configuration>
				<warName>${project.artifactId}##${maven.build.timestamp}</warName>
				<packagingExcludes>%regex[WEB-INF/lib/(?!mylib-1.0.0-SNAPSHOT).*.jar]</packagingExcludes>
			</configuration>
		</plugin>
	</plugins>
</build>

在项目根目录下执行命令

mvn package

生成 war 包，如 portal##20140922.war。

2. 部署

将 war 包上传到/anyfish_web/war/warHub 下后，执行部署脚本 parallelDeploy.sh （脚本内容见下）

部署脚本

并行部署脚本 parallelDeploy.sh 的功能：搜寻指定目录下最新的 war 包，然后依 Tomcat 格式，在 $TOMCAT_HOME/conf/Catalina/localhost 创建配置文件（如 portal##20140922.xml），以使 Tomcat 感知并部署此 web 工程。

# conf
ctx=portal
warFolder=/anyfish_web/war/warHub
deployFolder=/anyfish_web/war
confFolder=/Tomcat/conf/Catalina/localhost
# ---
latestWarFile=$(basename `ls -tr $warFolder/*.war | tail -n 1`)
echo --- latestWarFile: $latestWarFile
cp $warFolder/$latestWarFile $deployFolder/
confFile=$(echo $latestWarFile | sed 's/.*\#\#\(.*\)\.war/\1/')
ctxXml=$confFolder/$ctx##$confFile.xml
# generate context conf file for tomcat to deploy
echo --- ctxXml: $ctxXml
ctxCont='<Context displayName="'$ctx'" docBase="/anyfish_web/war/'$latestWarFile'" reloadable="true" />'
echo $ctxCont > $ctxXml

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Change Shell Prompt Color

2014-09-19

Normal user: vi ~/.bashrc

1	export PS1="\n\e[0;33m[\t \u@\h \W]\$ \e[m"

Root user (set as red #):

1	export PS1="\n\e[0;31m[\t \u@\h \W]\$ \e[m"

References:

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Recognizing Session Timeout

2014-09-07

You need to implement the HttpSessionListener interface. It receives notification events when session is created, or destroyed. In particular, its method sessionDestroyed(HttpSessionEvent se) gets called when the session is destroyed, which happens after timeout period has finished / session was invalidated. You can get the information stored in the session via HttpSessionEvent#getSession() call, and later do any arrangements that are necessary with the session. Also, be sure to register your session listener in web.xml:

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<listener>
    <listener-class>FQN of your sessin listener implementation</listener-class>
</listener>

If you ultimately want to distinguish between invalidation and session timeout you could use the following line in your listener:

1 2	long now = new java.util.Date().getTime(); boolean timeout = (now - session.getLastAccessedTime()) >= ((long)session.getMaxInactiveInterval() * 1000L);

Reference:

stackoverflow

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Use Encrypted Password Property in Spring Properties File

2014-08-23

Add dependencies in pom.xml:

<dependency>
	<groupId>org.jasypt</groupId>
	<artifactId>jasypt</artifactId>
	<version>1.9.2</version>
</dependency>
<dependency>
	<groupId>org.jasypt</groupId>
	<artifactId>jasypt-spring31</artifactId>
	<version>1.9.2</version>
</dependency>

Config applicationContextm.xml:

<bean id="textEncryptor" class="org.jasypt.util.text.BasicTextEncryptor" p:password="ur-pa55w0rd"/>
<beans profile="development">
	<!-- <context:property-placeholder ignore-resource-not-found="true"
		location="classpath*:/application.properties,
         			  classpath*:/application.development.properties"
         	file-encoding="utf-8" /> -->
       <bean class="org.jasypt.spring31.properties.EncryptablePropertySourcesPlaceholderConfigurer">
           <constructor-arg ref="textEncryptor" />
           <property name="locations">
               <list>
                   <value>classpath*:/application.properties</value>
                   <value>classpath*:/application.development.properties</value>
               </list>
           </property>
       </bean>
</beans>

P.S. Below snippet is not working. Wonder why.

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<bean class="org.jasypt.spring31.properties.EncryptablePropertyPlaceholderConfigurer"
            p:locations="classpath*:/application.properties,
        			  classpath*:/application.development.properties" c:textEncryptor-ref="textEncryptor" />

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Run a Program as Adminitrator via The Command Line

2014-08-12

Create a *.vbs script file:

Set objShell = CreateObject("Shell.Application")
prog = "c:/path/to/the/executable.exe"
args = ""
objShell.ShellExecute prog, args, "", "runas"

Then run it from command line, or via Launchy.

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