Speaking Java

Have you ever come across a situation where you wanted to retry a method invocation automatically? Let's say you are calling a stock ticker service for a given stock and get a transient error. Since it is a transient error, you will try again and it may work in second attempt. But what if it doesn't? Well, you will try third time. But how many times can you try like that? More importantly after how much time will you retry? Imagine if you have a handful of methods like this. Your code will become convoluted with retry logic. Is there a better way? Well, if you are using spring/spring boot, you are in luck. Here is how you can do that using spring. Let's write our business service as follows. import java.time.LocalDateTime; import java.util.concurrent.CompletableFuture; import lombok.extern.slf4j.Slf4j; import org.springframework.retry.annotation.Backoff; import org.springframework.retry.annotation.Retryable; import org.springframework.scheduling.annotation.Async; import...

In the last post we saw how to spin a http/2 server using embedded jetty. In this post we will see, how to use asynchronous servlet (as well as AIO a.k.a non-blocking IO) and why that is important? Asynchronous Servlets ≠ Asynchronous IO [1] The concept of Asynchronous Servlets is often confused with Asynchronous IO or the use of NIO. However, Asynchronous Servlets are not primarily motivated by asynchronous IO, since: HTTP Requests are mostly small and arrive in a single packet. Servlets rarely block on requests. Many responses are small and fit within the server buffers, so servlets often do not block writing responses. Asynchronous Servlets Use-case The main use-case for asynchronous servlets is waiting for non-IO events or resources. Many web applications need to wait at some stage during the processing of a HTTP request, for example: waiting for a resource to be available before processing the request (e.g., thread, JDBC Connection) waiting for an applica...

Have you ever wanted to configure internal Java servers using HTTP/2 (or H2 in short), because of the following advantages? Internal clients making concurrent calls, can now use a single connection by utilizing the multiplexing nature of HTTP/2. Server will/can use less threads as there are less connections overall. Servers can also push resources/data and can communicate using websockets But what if you don’t want to go through tedious process of setting up SSL/TLS certificates? HTTP/2 insists on SSL/TLS as no browser supports HTTP/2 on insecure mode. Or what if you want to save every bit of CPU and time by skipping encryption and decryption? You are at the right place. Since everyone nowadays is moving towards (or talking about) micro services, we will also configure Jetty HTTP/2 server in embedded mode. What more? We are also going to configure our server to use Asynchronous Servlets and Asynchronous IO (aka non-blocking IO or NIO) in Part-2 of this article. ...

If you are a using any Java web server (such as Tomcat) or app server (such as Wildfly, JBoss or Glassfish), then you know that they dont listen on http port 80. Well, why does it have to listen on port 80? because if you want your user to specify only the url and not the port; for example, http://mydomain.com and not http://mydomain:8080 Note: throughout this article mydomain.com can be replaced with localhost, if your product is in development stage. Software used: Ubuntu apache2 Any Java web/app server What we want to achieve We are going to divert all user requests coming on port 80 to Tomcat running 8080 on the same host. Installation Run the following commands sudo apt-get install apache2 sudo apt-get install libxml2-dev sudo apt-get install libapache2-mod-proxy-html Note: If your ubuntu OS is latest, then you may not have libapache2-mod-proxy-html package. Instead run the following command. sudo a2enmod proxy_html Configuration 1. Append t...

Here let's see how we can install Windows 8 and (K)ubuntu 15.10 (Wily Werewolf) along side Mac Yosemite as triple boot. Software/Hardware required Mac book Pro 11,1 (instruction might be similar for newer models) Yosemite Windows 8 (K)Ubuntu 15.10  Wily Werewolf (might work with 15.04 as well) Refind (not reEFIt) Here is the summary of what we are going to do. Partition mac to have windows boot-camp partition  Install windows 8 Create two new partitions from mac partition for Linux Install (K)ubuntu Fix GPT-MBR Install Refind Step-0 In case you want to backup your mac:  Restart mac and hold  This will boot Mac in recovery mode as shown below    Plugin an external drive and choose Disk Utility option Select the mac partition (not your hard disk root) and go to restore tab Choose your external drive as the destination as shown below Important: ensure that your mac partition is the Source Click Restore to take a cop...

In the previous post we saw how to set up Keycloak . Here we will see how to generate and install GoDaddy.com certificate in Keycloak. The steps are similar for Wildfly as well. Step 1: Generate CSR file Run the following commands in your terminal. <mydomain.com> has to be replaced with your actual domain name. keytool -genkey -alias mydomain_com -keyalg RSA -keysize 2048 -keystore mydomain_com.jks keytool -certreq -alias mydomain_com -file mydomain_com.csr -keystore mydomain_com.jks Step 2: Generate certificate Upload  mydomain_com . csr  file content into GoDaddy.com, generate and download certificate for tomcat server (steps to generating SSL certificate is beyond the scope of this article). If you unzip the file, you will see the following files. gd_bundle-g2-g1.crt ..5f8c...3a89.crt   #some file with alphanumeric name gdig2.crt Files 1 and 2 are of our interest. Third file is not required. Step 3: Import certificate to key...

In this article we will see how to use Keycloak , one of the popular SSO software. Here is the excerpt from the official website. Integrated SSO and IDM for browser apps and RESTful web services.  Built on top of the OAuth 2.0, Open ID Connect, JSON Web Token (JWT) and SAML 2.0 specifications.  Keycloak has tight integration with a variety of platforms and has a HTTP security proxy service where we don't have tight integration.  Options are to deploy it with an existing app server, as a black-box appliance, or as an Openshift cloud service and/or cartridge. Installation Download the software from   here . Let's use  keycloak-1.4.0.Final   for the purpose of demonstration in this article and we will try to set it as a standalone server. To install first download either the zip or tar.gz and extract. Then start by running either: keycloak-1.4.0.Final/bin/standalone.sh or: keycloak-1.4.0.Final/bin/standalone.bat That's it. you are do...