try-with-resources

A known, and now kind of old feature of Java 7, but still isn't as popular as we wish.

Straightforward (and easy) implementation, where you need to declare resources (File, Stream) into parenthesis of "try" keyword:

private static void printFileJava7() throws IOException {

    try(InputStream input = new FileInputStream("hola.txt")) {

        int data = input.read();
        while(data != -1){
            System.out.print((char) data);
            data = input.read();
        }
    }
}

And JVM will have the responsibility to close those resources.

Beware: that the object in try() must implement AutoCloseable.

More info:

https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

http://tutorials.jenkov.com/java-exception-handling/try-with-resources.html

https://www.mkyong.com/java/try-with-resources-example-in-jdk-7/

HTTP Codes - Arquitectura Restful

La arquitectura Rest se basa fuertemente en el protocolo HTTP, por lo cual es importante responder (y parsear al recibir) los diferentes códigos HTTP que existen.
Los códigos están agrupados por las siguientes categorías:

• 1xx – Informational
• 2xx – Successful
• 3xx – Redirection
• 4xx - Client Error
• 5xx - Server Error

El proyecto  deberia uso granular de estos códigos con alguna libreria transversal.

Deberíamos usar solo los códigos más útiles (top “10”) que son los siguientes:

HTTP Response codes

200	OK	Successfully executed. should be used to indicate nonspecific success
201	CREATED	Successfully executed and a new resources has been created. The response body is either empty or contains a URI(s) of the created resource. The location header should should also contain the new URI
202	ACCEPTED	The request was valid and has been accepted but has not yet been processed. The response should include a URI to poll for status updates on the request. Allows for asynchronous request ( start of an asynchronous action)
204	NO_CONTENT	The request was successful but the server did not have a response. should be used when the response body is intentionally empty. Ejemplo: Si se busca el listado de productos para un cliente y el cliente existe pero la lista es vacía, el estado es 204
301	MOVED_PERMANENTLY	The new location should be returned in the response ( should be used to relocate resources)
302	REDIRECT	The HTTP response status code 302 Found is a common way of performing URL redirection.
400	BAD_REQUEST	Malformed or invalid request
401	UNAUTHORIZED	Invalid authorization credentials. (no autenticado, o autenticado incorrectamente)
403	FORBIDDEN	Disallowed request. Security error. (no autorizado para ver pagina/recurso)
404	NOT_FOUND	Resource not found. Ejemplo: Si se busca un cliente por rut y éste no existe, el estado es 404
405	METHOD_NOT_ALLOWED	Method (verb) not allowed for requested resource. Response will provide an “Allow” header to indicate what is allowed
412	PRECONDITION_FAILED	One or more conditions given in the request header fields evaluated to false when tested on the server.
415	UNSUPPORTED_MEDIA_TYPE	Client submitted a media type that is incompatible for the specified resource.
422	UNPROCESSABLE_ENTITY	Se ha producido un error funcional. El servicio reconoce los parámetros como válidos, pero alguna condición de negocio no se puede llevar a cabo. Ej: "Monto Pagado+monto capitalizado no puede ser mas que monto adeudado+monto vencido+monto adeudado ajuste-monto condonado para monto XXX" invocando a servicio bus para cálculo de pago.
418	I'm a teapot	Ludic HTTP
500	INTERNAL_SERVER_ERROR	Catchall for server processing problem
503	SERVICE_UNAVAILABLE	Response in the face of too many request
504	GATEWAY_TIMEOUT	server error response code indicates that the server, while acting as a gateway or proxy, did not get a response in time from the upstream server that it needed in order to complete the request.

HTTP verbs:
 

1. GET. The GET method requests a representation of the specified resource. Requests using GET should only retrieve data. (idempotent)
2. POST. The POST method is used to submit an entity to the specified resource, often causing a change in state or side effects on the server (payload)
3. HEAD. The HEAD method asks for a response identical to that of a GET request, but without the response body.
4. PUT. The PUT method replaces all current representations of the target resource with the request payload.
5. DELETE. The DELETE method deletes the specified resource.
6. CONNECT. The CONNECT method establishes a tunnel to the server identified by the target resource.
7. OPTIONS. The OPTIONS method is used to describe the communication options for the target resource.  OPTIONS sirve para verificar CORS!
8. TRACE. The TRACE method performs a message loop-back test along the path to the target resource.
   
9. PATCH. The PATCH method is used to apply partial modifications to a resource.

more details:

• HEAD - No defined body semantics.
• GET - No defined body semantics.
• DELETE - No defined body semantics.
• CONNECT - No defined body semantics

• PUT - Body supported.
• POST - Body supported.
• TRACE - Body not supported.
• OPTIONS - Body supported but no semantics on usage (maybe in the future).

Mayor información: 

•  https://en.wikipedia.org/wiki/List_of_HTTP_status_codes
•  https://hackernoon.com/restful-api-designing-guidelines-the-best-practices-60e1d954e7c9

Spring Batch Samples

Several examples of Spring Batch:

https://github.com/devwebcl/spring-batch

Simple HTTP Server

python -m SimpleHTTPServer 8000

if you face :
/usr/bin/python: No module named SimpleHTTPServer

it's because for python 3:

python3 -m http.server 8000

Cannot retrieve WLS app info

Cannot retrieve:

The configuration for app is still being loaded from your last request, please wait a moment and retry.

####<Oct 30, 2017 9:59:44 AM CLT> <Error> <Console> <lablnx297> <AdminServer> <[ACTIVE] ExecuteThread: '5' for queue: 'weblogic.kernel.Default (self-tuning)'> <weblogic> <> <cc19eb40-e1ae-46e5-80cb-dbf2a3509811-00000f0c> <1509368384819> <BEA-240003> <Administration Console encountered the following error: java.lang.NullPointerException
  at weblogic.application.internal.ApplicationRuntimeMBeanImpl.getComponentRuntimes(ApplicationRuntimeMBeanImpl.java:449)
  at sun.reflect.GeneratedMethodAccessor1348.invoke(Unknown Source)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:606)
  at weblogic.management.jmx.modelmbean.WLSModelMBean.getAttribute(WLSModelMBean.java:525)
  at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.getAttribute(DefaultMBeanServerInterceptor.java:647)
  at com.sun.jmx.mbeanserver.JmxMBeanServer.getAttribute(JmxMBeanServer.java:678)
  at weblogic.management.jmx.mbeanserver.WLSMBeanServerInterceptorBase$12.run(WLSMBeanServerInterceptorBase.java:326)
  at java.security.AccessController.doPrivileged(Native Method)
  at weblogic.management.jmx.mbeanserver.WLSMBeanServerInterceptorBase.getAttribute(WLSMBeanServerInterceptorBase.java:324)
  at weblogic.management.mbeanservers.internal.JMXContextInterceptor.getAttribute(JMXContextInterceptor.java:157)
  at weblogic.management.jmx.mbeanserver.WLSMBeanServerInterceptorBase$12.run(WLSMBeanServerInterceptorBase.java:326)
  at java.security.AccessController.doPrivileged(Native Method)
  at weblogic.management.jmx.mbeanserver.WLSMBeanServerInterceptorBase.getAttribute(WLSMBeanServerInterceptorBase.java:324)
  at weblogic.management.mbeanservers.internal.SecurityInterceptor.getAttribute(SecurityInterceptor.java:300)
  at weblogic.management.jmx.mbeanserver.WLSMBeanServer.getAttribute(WLSMBeanServer.java:279)
  at weblogic.management.mbeanservers.internal.JMXConnectorSubjectForwarder$5$1.run(JMXConnectorSubjectForwarder.java:327)
  at java.security.AccessController.doPrivileged(Native Method)
  at weblogic.management.mbeanservers.internal.JMXConnectorSubjectForwarder$5.run(JMXConnectorSubjectForwarder.java:325)
  at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:363)
  at weblogic.management.mbeanservers.internal.JMXConnectorSubjectForwarder.getAttribute(JMXConnectorSubjectForwarder.java:320)
  at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468)
  at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:97)
  at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1332)
  at java.security.AccessController.doPrivileged(Native Method)
  at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1431)
  at javax.management.remote.rmi.RMIConnectionImpl.getAttribute(RMIConnectionImpl.java:661)
  at javax.management.remote.rmi.RMIConnectionImpl_WLSkel.invoke(Unknown Source)
  at weblogic.rmi.internal.BasicServerRef.invoke(BasicServerRef.java:701)
  at weblogic.rmi.internal.BasicServerRef$1.run(BasicServerRef.java:527)
  at weblogic.security.acl.internal.AuthenticatedSubject.doAs(AuthenticatedSubject.java:363)
  at weblogic.security.service.SecurityManager.runAs(SecurityManager.java:146)
  at weblogic.rmi.internal.BasicServerRef.handleRequest(BasicServerRef.java:523)
  at weblogic.rmi.internal.wls.WLSExecuteRequest.run(WLSExecuteRequest.java:118)
  at weblogic.work.ExecuteThread.execute(ExecuteThread.java:311)
  at weblogic.work.ExecuteThread.run(ExecuteThread.java:263)
>

HTTP Cluster WebLogic Server

Old Deprecated feature:

web.xml :

<servlet><servlet-name>ProxyServlet</servlet-name>
<servlet-class>weblogic.servlet.proxy.HttpProxyServlet</servlet-class>
<init-param>
<param-name>redirectURL</param-name>
<param-value>http://localhost:8080</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ProxyServlet</servlet-name>
<url-pattern>/MyProducerApp/*</url-pattern>
</servlet-mapping>

.

Clear Cache WLS

Before deleting any directory, you need to shutdown all servers first.

The following provides a generic example path to the tmp directory in question:

WINDOWS: 
cd C:\wls\user_projects\domains\servers\

UNIX:
cd /wls/user_projects/domains/servers/

The following would be used to clear the cache:

WINDOWS:  
rd C:\wls\user_projects\domains\servers\tmp
rd C:\wls\user_projects\domains\servers\cache

UNIX: 
rm -rf /wls/user_projects/domains/servers/tmp
rm -rf /wls/user_projects/domains//servers/cache


 For WLS versions 9.2 and above, delete the following Admin and Managed server cache directories:

    /servers/cache
    /servers/stage (if exists)
    /servers/tmp
 

WLS JMS Configuration

Essential steps to configure a JMS environment


CORE_WLS_Domain --> Services --> Persistent Stores -->

New:

Name: FileStore-Mensajeria1
Target: Managed Server 1 (WLS01)
Directory: jmsMensajeria_1
(Activate Changes)

Name: FileStore-Mensajeria2
Target: Managed Server 2 (WLSS02)
Directory: jmsMensajeria_2
(Activate Changes)


CORE_WLS_Domain --> Services --> Messaging --> JMS Servers

New:

Name: JMSServer-Mensajeria_1
Persistent Store: FileStore-Mensajeria1
Target: WLS01 (migratable)
(finish)

Name: JMSServer-Mensajeria_2
Persistent Store: FileStore-Mensajeria2
Target: WLS02 (migratable)
(finish)

(Activate Changes)


CORE_WLS_Domain --> Services --> Messaging --> JMS Modules

Name: JMSModule_Mensajeria
Target: wls_core_cluster
(next/finish)
(Activate Changes)


entrar a JMS Module creado: (crear subdeployment)
CORE_WLS_Domain --> Services --> Messaging --> JMS Modules --> JMSModule_Mensajeria --> Subdeployments

New:

name: MensajeriaSubdeployment
Target: JMSServer-Mensajeria_1, JMSServer-Mensajeria_2
(Activate Changes)


CORE_WLS_Domain --> Services --> Messaging --> JMS Modules --> JMSModule_Mensajeria

New:

Connection Factory (next)

Name: ConnectionFactory-Mensajeria
JNDI Name: jms/ConnectionFactory-Mensajeria (next)
(finish)
(Activate Changes)

New:

Distributed Queue (next)

Name: DistributedQueue-Mensajeria
JNDI Name: jms/journal-standar (next)
Advanced Targeting: MensajeriaSubdeployment

JMS Servers: JMSServer-Mensajeria_1, JMSServer-Mensajeria_2
(finish)
(Activate Changes)

Opatch WLS 12c

Backup Oracle Home:
It is highly recommended that you back up the Oracle home before any patch operation. You can back up the Oracle home using your preferred method. You can use any method such as zip, cp -r, tar, and cpio to compress the Oracle home.

Opatch path:
/Users/German/Oracle/Middleware/Oracle_Home/OPatch

List patches:
./opatch lsinventory
./opatch lsinventory -detail

Check if it's feasible:
./opatch apply /Users/German/tmp/patches/23639929 -report

if the next message appears:

JAVA_HOME is not set or does not exist

then add (jre path) :

-jre /Library/Java/JavaVirtualMachines/jdk1.7.0_201.jdk/Contents/Home

Apply patch:
./opatch apply /Users/German/tmp/patches/23639929

Rollback patch
./opatch rollback -id 23639929

logs:

ORACLE_HOME/cfgtoollogs/opatch/

More info:
https://docs.oracle.com/middleware/1213/core/OPATC/toc.htm

Too many open files

The following problem may occurr in WLS:

Caused By: java.net.SocketException: Too many open files
  at java.net.Socket.createImpl(Socket.java:447)
  at java.net.Socket.connect(Socket.java:577)
  at oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:161)
  at oracle.net.nt.ConnOption.connect(ConnOption.java:159)
  at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:428)
  at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:506)
  at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:595)
  at oracle.net.ns.NSProtocol.connect(NSProtocol.java:230)

This is a common issue when  File Descriptors are not enough for the OS processes.

Checking the most open FD appear WLS Managed Servers and they are almost on the limit:

4076 376 /u04/Middleware/WLS12c/jdk/bin/java-server-Xms1024m-Xmx2048m-XX:PermSize=256m-XX:MaxPermSize=512m-Dweblogic.Name=WLS02

4063 32526 /u04/Middleware/WLS12c/jdk/bin/java-server-Xms1024m-Xmx2048m-XX:PermSize=256m-XX:MaxPermSize=512m-Dweblogic.Name=WLS01

Checking with lsof -p <pid> we see a lot of open jar files from war files, because we have several war files deployed.

Check:

$ ulimit -n
4096

Therefore the solution is to set a bigger soft & hard limit.