Bermula dengan Mule ESB

1. Gambaran keseluruhan

Mule ESB adalah Bas Perkhidmatan Perusahaan berasaskan Java yang ringan. Ini membolehkan pemaju untuk menghubungkan beberapa aplikasi bersama-sama dengan bertukar data dalam format yang berbeza. Ia membawa data dalam bentuk mesej.

ESB menawarkan kemampuan yang hebat dengan menyediakan sejumlah perkhidmatan, seperti:

  • Pembuatan dan hosting perkhidmatan
  • Pengantaraan perkhidmatan
  • Penghantaran mesej
  • Transformasi data

Kami akan dapati ESB berguna sekiranya kita perlu menggabungkan pelbagai aplikasi bersama-sama, atau jika kita mempunyai idea untuk menambahkan lebih banyak aplikasi pada masa akan datang.

ESB juga digunakan untuk menangani lebih dari satu jenis protokol komunikasi dan ketika kemampuan perutean pesan diperlukan.

Mari buat contoh projek di Bahagian 5 menggunakan AnyPoint Studio yang boleh dimuat turun di sini.

2. Struktur Mule Mesej

Ringkasnya, tujuan utama ESB adalah untuk memediasi antara perkhidmatan dan menghantar mesej ke pelbagai titik akhir. Oleh itu, ia perlu menangani pelbagai jenis kandungan atau muatan.

Struktur mesej terbahagi kepada dua bahagian:

  • Tajuk, yangmengandungi metadata mesej
  • Muatan, yang mengandungi data khusus perniagaan

Mesej tersemat dalam objek mesej. Kita boleh mengambil objek mesej dari konteks. Kita dapat mengubah sifat dan muatannya menggunakan komponen dan transformer Java khusus di dalam aliran Mule.

Setiap aplikasi terdiri daripada satu atau lebih aliran.

Dalam arus, kita dapat menggunakan komponen untuk mengakses, menyaring atau mengubah pesan dan sifatnya yang berbeza.

Sebagai contoh, kita dapat memperoleh contoh pesan menggunakan komponen Java. Komponen alat kelas Dipanggil muka dari org.mule.api.lifecycle pakej:

public Object onCall(MuleEventContext eventContext) throws Exception { MuleMessage message = eventContext.getMessage(); message.setPayload("Message payload is changed here."); return message; }

3. Sifat dan Pemboleh ubah

Metadata mesej terdiri daripada sifat. Pemboleh ubah mewakili data mengenai mesej. Bagaimana sifat dan pemboleh ubah diterapkan pada kitaran hidup mesej ditentukan oleh ruang lingkupnya. Hartanah boleh terdiri daripada dua jenis, berdasarkan skopnya: masuk dan keluar.

Sifat masuk mengandungi metadata yang menghalang mesej menjadi tidak teratur ketika melintasi aliran. Sifat masuk tidak berubah dan tidak dapat diubah oleh pengguna. Mereka hanya hadir sepanjang aliran - setelah mesej keluar dari aliran, sifat masuk tidak lagi ada.

Sifat keluar boleh ditetapkan secara automatik oleh Mule, atau pengguna dapat menetapkannya melalui konfigurasi aliran. Sifat-sifat ini boleh berubah. Mereka menjadi sifat masuk apabila pesan memasuki aliran lain setelah melintasi halangan pengangkutan.

Kami boleh menetapkan dan mendapatkan sifat keluar dan masuk masing-masing dengan memanggil kaedah setter dan getter yang berkaitan dalam ruang lingkup masing-masing:

message.setProperty( "outboundKey", "outboundpropertyvalue", PropertyScope.OUTBOUND); String inboundProp = (String) message.getInboundProperty("outboundKey");

Terdapat dua jenis pemboleh ubah yang tersedia untuk dinyatakan dalam aplikasi.

Salah satunya adalah pemboleh ubah aliran yang bersifat tempatan untuk aliran Mule dan tersedia melintasi aliran, sub-aliran dan aliran swasta.

Pemboleh ubah sesi setelah diisytiharkan menjadi tersedia di seluruh aplikasi.

4. Penghalang Pengangkutan dan aliran-ref

Penghalang pengangkutan adalah penyambung HTTP, VM, JMS atau penyambung serupa yang memerlukan jalan atau titik akhir agar mesej dihantar. Pemboleh ubah aliran tidak tersedia melintasi halangan pengangkutan, tetapi pemboleh ubah sesi tersedia di seluruh projek dalam semua aliran.

Apabila kita perlu membuat aliran bawah atau aliran peribadi, kita dapat merujuk kepada aliran dari aliran induk atau aliran lain menggunakan komponen aliran-ref . Kedua-dua pemboleh ubah aliran dan pemboleh ubah sesi terdapat dalam sub-aliran dan aliran swasta yang disebut dengan menggunakan aliran-ref .

5. Contoh Projek

Mari buat aplikasi di Anypoint Studio yang mengandungi pelbagai aliran, yang berkomunikasi antara mereka melalui penyambung masuk dan keluar.

Mari lihat aliran pertama:

Kita boleh mengkonfigurasi pendengar HTTP sebagai:

Komponen aliran mesti berada di dalam a teg. Jadi, aliran contoh dengan pelbagai komponen adalah:

Di dalam aliran, kami memberikan rujukan kepada pendengar HTTP yang dikonfigurasi. Kemudian kami menyimpan logger untuk mencatat muatan yang diterima pendengar HTTP melalui kaedah POST.

Setelah itu, kelas pengubah Java khusus ditempatkan, yang mengubah muatan setelah menerima mesej:

public Object transformMessage( MuleMessage message, String outputEncoding) throws TransformerException { message.setPayload("Payload is transferred here."); message.setProperty( "outboundKey", "outboundpropertyvalue", PropertyScope.OUTBOUND); return message; }

Kelas transformer mesti meluaskan AbstractMessageTransformer . Kami juga menetapkan harta keluar masuk kelas.

Sekarang, kami telah menukar muatan di dalam objek mesej, dan memasukkannya ke dalam konsol menggunakan logger. Kami menetapkan pemboleh ubah aliran dan pemboleh ubah sesi.

Finally, we are sending our payload through outbound VM connector. The path in VM connector determines the receiving endpoint:

The message carried and transformed by the initial flow reaches Flow1 through an inbound VM endpoint.

The Java component retrieves outbound properties set by the first flow and returns the object which becomes the message payload.

The transformMessage() method for this task:

public Object transformMessage( MuleMessage message, String outputEncoding) throws TransformerException { return (String) message.getInboundProperty("outboundKey"); }

Then, flow and session variables are set to the second flow. After that, we've got a reference to Flow2 using flow-ref component.

In Flow2, we've transformed the message using Java component class and logged it in the console. We've also set a flow variable F3.

After calling Flow2 using flow-ref, Flow1 will wait for the message to be processed in Flow2.

Any flow variable set in Flow1 and Flow2 will be available in both flows since these flows aren't separated by any transport barriers.

Finally, the message is sent back to the HTTP requester through VMs. We configured all VMs as request-response.

We can invoke this application from any REST client by posting any JSON data in the body. The URL will be localhost:8081 as configured in HTTP listener.

6. Maven Archetype

We can build a Mule ESB project using Mulesoft's Maven archetype.

In Maven's settings.xml file, we first need to add the org.mule.tools plugin group:

 org.mule.tools 

Then, we need to add a profile tag that says where Maven should look for Mulesoft artifacts:

 Mule Org  true    mulesoft-releases MuleSoft Repository //repository-master.mulesoft.org/releases/ default   

Finally, we can create the project using mule-project-archetype:create:

mvn mule-project-archetype:create -DartifactId=muleesb -DmuleVersion=3.9.0

After configuring our project, we can create a deployable archive using mvn package.

After that, we'd deploy the archive into the apps folder of any standalone Mule server.

7. A Standalone Mule Server via MuleSoft's Maven Repository

As just noted, the project we just created requires a standalone Mule server.

If we don't already have one, we can edit our pom.xml to pull one from MuleSoft's Maven repository:

 org.mule.tools.maven mule-maven-plugin 2.2.1  standalone 3.9.0    deploy deploy  deploy    

8. Conclusion

In this article, we've gone through different necessary concepts of building as ESB application in Mule. We've created a sample project illustrating all the described concepts.

We can now start creating ESB application using Anypoint Studio to meet our various needs.

As usual, the complete project can be found over on GitHub.

1. Overview

Mule ESB is a lightweight Java-based Enterprise Service Bus. It allows developers to connect multiple applications together by exchanging data in different formats. It carries data in the form of a message.

ESBs offer powerful capabilities by providing a number of services, such as:

  • Service creation and hosting
  • Service mediation
  • Message routing
  • Data transformation

We'll find ESBs useful if we need to integrate multiple applications together, or if we have the notion of adding more applications in the future.

ESB is also used for dealing with more than one type of communication protocol and when message routing capabilities are required.

Let's create a sample project in Section 5 using AnyPoint Studio which is available for download here.

2. Mule Message Structure

Simply put, the primary purpose of an ESB is to mediate between services and route messages to various endpoints. So it needs to deal with different types of content or payload.

The message structure is divided into two parts:

  • The header, whichcontains message metadata
  • The payload, which contains business-specific data

The message is embedded within a message object. We can retrieve the message object from the context. We can change its properties and payload using custom Java components and transformers inside a Mule flow.

Each application consists of one or more flows.

In a flow, we can use components to access, filter or alter a message and its different properties.

For example, we can obtain an instance of a message using Java component. This component class implements a Callable interface from org.mule.api.lifecycle package:

public Object onCall(MuleEventContext eventContext) throws Exception { MuleMessage message = eventContext.getMessage(); message.setPayload("Message payload is changed here."); return message; }

3. Properties and Variables

Message metadata consists of properties. Variables represent data about a message. How properties and variables are applied across the message's life-cycle is defined by their scopes. Properties can be of two types, based on their scope: inbound and outbound.

Inbound properties contain metadata that prevents messages to become scrambled while traversing across flows. Inbound properties are immutable and cannot be altered by the user. They're present only for the duration of the flow – once the message exits the flow, inbound properties are no longer there.

Outbound properties can be set automatically by Mule, or a user can set them through flow configuration. These properties are mutable. They become inbound properties when a message enters another flow after crossing transport-barriers.

We can set and get outbound and inbound properties respectively by calling associated setter and getter methods in their respective scopes:

message.setProperty( "outboundKey", "outboundpropertyvalue", PropertyScope.OUTBOUND); String inboundProp = (String) message.getInboundProperty("outboundKey");

There are two types of variables available to declare in applications.

One is flow variable which is local to a Mule flow and available across the flow, sub-flows and private flows.

Session variables once declared become available across the entire application.

4. Transport Barriers and flow-ref

Transport barriers are HTTP-connectors, VMs, JMS or similar connectors that require paths or endpoints for messages to be routed. Flow variables aren't available across transport barriers, but session variables are available across the project in all flows.

When we need to create sub-flow or private flow, we can refer to the flow from a parent or another flow using flow-ref component. Both flow variables and session variables are available in sub-flows and private flows referred to using flow-ref.

5. Example Project

Let's create an application in Anypoint Studio that contains multiple flows, which communicate between themselves through inbound and outbound connectors.

Let's look at the first flow:

We can configure an HTTP listener as:

Flow components must be inside a tag. So, an example flow with multiple components is:

Inside the flow, we're providing a reference to a configured HTTP listener. Then we're keeping a logger to log the payload that HTTP listener is receiving through POST method.

After that, a custom Java transformer class is placed, that transforms the payload after receiving the message:

public Object transformMessage( MuleMessage message, String outputEncoding) throws TransformerException { message.setPayload("Payload is transferred here."); message.setProperty( "outboundKey", "outboundpropertyvalue", PropertyScope.OUTBOUND); return message; }

The transformer class must extend AbstractMessageTransformer. We're also setting an outbound property inside the class.

Now, we have already converted payload inside the message object, and have logged that in the console using logger. We're setting a flow variable and a session variable.

Finally, we are sending our payload through outbound VM connector. The path in VM connector determines the receiving endpoint:

The message carried and transformed by the initial flow reaches Flow1 through an inbound VM endpoint.

The Java component retrieves outbound properties set by the first flow and returns the object which becomes the message payload.

The transformMessage() method for this task:

public Object transformMessage( MuleMessage message, String outputEncoding) throws TransformerException { return (String) message.getInboundProperty("outboundKey"); }

Then, flow and session variables are set to the second flow. After that, we've got a reference to Flow2 using flow-ref component.

In Flow2, we've transformed the message using Java component class and logged it in the console. We've also set a flow variable F3.

After calling Flow2 using flow-ref, Flow1 will wait for the message to be processed in Flow2.

Any flow variable set in Flow1 and Flow2 will be available in both flows since these flows aren't separated by any transport barriers.

Finally, the message is sent back to the HTTP requester through VMs. We configured all VMs as request-response.

We can invoke this application from any REST client by posting any JSON data in the body. The URL will be localhost:8081 as configured in HTTP listener.

6. Maven Archetype

We can build a Mule ESB project using Mulesoft's Maven archetype.

In Maven's settings.xml file, we first need to add the org.mule.tools plugin group:

 org.mule.tools 

Then, we need to add a profile tag that says where Maven should look for Mulesoft artifacts:

 Mule Org  true    mulesoft-releases MuleSoft Repository //repository-master.mulesoft.org/releases/ default   

Finally, we can create the project using mule-project-archetype:create:

mvn mule-project-archetype:create -DartifactId=muleesb -DmuleVersion=3.9.0

After configuring our project, we can create a deployable archive using mvn package.

After that, we'd deploy the archive into the apps folder of any standalone Mule server.

7. A Standalone Mule Server via MuleSoft's Maven Repository

As just noted, the project we just created requires a standalone Mule server.

Sekiranya kita belum memilikinya, kita dapat mengedit pom.xml kita untuk menariknya dari repositori MuleSoft's Maven:

 org.mule.tools.maven mule-maven-plugin 2.2.1  standalone 3.9.0    deploy deploy  deploy    

8. Kesimpulannya

Dalam artikel ini, kami telah melalui pelbagai konsep pembinaan yang diperlukan sebagai aplikasi ESB di Mule. Kami telah membuat contoh projek yang menggambarkan semua konsep yang dijelaskan.

Kita sekarang boleh mula membuat aplikasi ESB menggunakan Anypoint Studio untuk memenuhi pelbagai keperluan kita.

Seperti biasa, projek lengkap boleh didapati di GitHub.