This article will introduce the basic concepts of JGroups and then implement a task java,spring boot,errror response,http,tutorial,customize. JGroups is a library for reliable one-to-one or one-to-many communication written in the Java language. It can be used to create groups of processes whose. JGroup is the corner stone for clustering. It is a reliable multicast system. As we know, using IP multicasting we can set a group of computers to.
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Running a Demo Program Using JGroups without a network Writing a simple application Creating a channel and joining a cluster The main event loop and sending chat messages Receiving messages and view change notifications Trying out the SimpleChat application The goal is to show how to configure JGroups and how to write a simple application showing the major methods of the API.
Download JGroups can be downloaded here . For this tutorial, I’m using the binary version of JGroups 2. Note that JGroups 2. The contents of the directory are  http: Screenshot tutorrial the JGroups binary distribution The most important files are: This might get dropped in 3.
JGroups functionality, including demo and junit apps.
If a smaller JAR is required, this can be done by downloading the source distribution and invoking the “jar” target, which creates a jgroupscore. TCP based stack with dynamic discovery sfc. UDP using IP multicasting based stack with simple flow control tcp-nio.
If you use the log4j logging system, you also have to add log4j. As an alternative, you can also use jgroups. Testing your Setup To see whether your system can find the JGroups classes, execute the following command: Version or java -jar jgroups-all. Running a Demo Program To test whether JGroups works okay on your machine, run the following command twice: Draw 2 whiteboard windows should appear as shown in Figure 1.
Screenshot of 2 Draw instances If you started them simultaneously, they could initially show a membership of 1 in their title bars.
After some time, both windows should show 2. This means that the two instances found each other and formed a group. When drawing in one window, the second instance should also be updated.
As the default group transport uses IP multicast, make sure that jgroup if you want start the 2 instances in different subnets – IP multicast is enabled. If this is not the case, the 2 instances won’t ‘find’ each other and the sample won’t work. If the 2 instances find each other and form a cluster, igroups can skip ahead to the next chapter “Writing a simple application”.
Using JGroups without a tutofial You may skip this section if the 2 instances found each other correctly in the previous section. Sometimes there isn’t a network connection e.
DSL modem is downor we want to multicast only on the local machine. To do this, we can use the loopback device Draw You should again see 2 instances of Draw which form a cluster. If this is not the case, you may have to add a multicast route to the loopback device this requires superuser or admin privileges: If no route for multicast traffic is added, the default will be to use the fdefault gateway, which will typically direct the multicast traffic towards the ISP.
To prevent this e. ISP drops multicast traffic, or latency is too highwe recommend to add a route for multicast traffic which tutofial to the internal network e. In a nutshell, there are multiple possible reasons the cluster doesn’t form: A firewall discards packets.
To verify this, turn the firewall off.
If the cluster forms, then turn the firewall back on and selectively add rules to let JGroups traffic pass. You don’t use the right network interface NIC: There is no multicast route for jgrousp chosen NIC. All instances of SimpleChat find each other and form a cluster. There is no need to run a central chat server to which instances have to connect. Therefore, there is no single point of failure. A message is sent to all instances of the cluster. An instance gets a notification callback when another instance leaves or crashes and when other instances join.
Optional We maintain jgrojps common cluster-wide shared state, e. New instances acquire that history from existing instances.
JGroups overview JGroups uses a JChannel as the main API to connect to a cluster, send and tutorixl messages, and to register listeners that are called when things such as member joins happen.
What is sent around are Messages, which contain a byte buffer the tutorualplus the sender’s and receiver’s address. Addresses are subclasses of org. Address, and usually contain an IP address plus a port. The list of instances in a cluster is called a view org. Viewand every instance contains exactly the same View. Tutoril list of the addresses of all instances can get retrieved by calling Tutoriao.
Instances can only send or receive messages when they’ve joined a cluster. When an instance wants to leave the cluster, methods JChannel. The latter actually calls disconnect if the channel is still connected before closing the channel. Creating a channel and joining a cluster To join a cluster, we’ll use a JChannel. An instance of JChannel is created with a configuration e.
To actually connect to the cluster, the connect String name method is used.
All channel instances which call connect with the same argument will join the same cluster. So, let’s actually create a JChannel and connect to a cluster called “ChatCluster”: This configures the channel with the default properties. Alternatively, we could pass an XML file to configure the channel, e. The connect method joins cluster “ChatCluster”. Note that we don’t need to explicitly create a cluster beforehand; connect creates the cluster if it is the first instance.
All instances which join the same cluster will be in the same cluster of course! The main event loop and sending chat messages We now run an event loop, which reads input from stdin ‘a message’ and sends it to all instances currently in the cluster. When “exit” or “quit” quit are entered, we fall out of the loop and close the channel. The event loop blocks until a new line is ready from standard inputthen sends a message to the cluster. This is done by creating a new Message and calling Channel.
The first argument of the Message constructor is the destination address. A null destination address means send the message to everyone in the cluster a non-null address of an instance would send a message from us to only 1 instance.
The second argument is our own address. This is null as well, as the stack will insert the correct address anyway.
The third argument is the line that we read from stdin, this uses Java serialization to create a byte buffer and set the message’s payload to it. Note that we could also serialize the object ourselves which is actually the recommended way! The application is now fully functional, except that we don’t yet receive messages or view notifications.
This is done in the next section below. Receiving messages and view change notifications Let’s now register as a Receiver to receive message and view changes.
To this end, we could implement org. Receiver with 6 methodshowever, I chose to extend ReceiverAdapter which has default implementations, and only override callbacks tutlrial and viewChange we’re interested in. We now need to extend ReceiverAdapter: Its toString method prints out the view ID an increasing ID and a list of the current instances in the cluster In receivewe get a Message as argument. We simply get its buffer as an object again using Java serialization and print it igroups stdout.
Jgrops also print the sender’s address Message. Note that we could also get the byte buffer the payload by calling Message. Trying out the SimpleChat application Now that the demo chat application is fully functional, let’s try it out. Start an instances of SimpleChat: It is the only instance so far. So let’s start the second instance and type something: Note that the first instance tutoriwl The instances are listed in order of joining the cluster, with the oldest instance as first element.