Connecting Java Chassis Applications to ServiceComb Engines

This section describes how to connect Java chassis applications to ServiceComb engines and use the most common functions of ServiceComb engines. For details about the development guide, see Using ServiceComb Engine Functions.

In the Apache ServiceComb Samples project, you can find the code corresponding to the development methods in this section.

Prerequisites

Microservice applications have been developed based on Java chassis.
For details about microservice application development in the Java chassis framework, see https://servicecomb.apache.org/references/java-chassis/en_US/.
Version requirements. See Requirements for Microservice Development Framework of a ServiceComb Engine.
This document assumes that you use Maven for dependency management and packaging in your project. You are familiar with the Maven dependency management mechanism and are able to modify the dependency management and dependency in the pom.xml file.
Java chassis can be used together with different technologies. The name of the configuration file is related to the technology you use. For example, if you use Java chassis in Spring mode, the configuration file name is microservice.yaml. If you use Java chassis in Spring Boot mode, the configuration file name is application.yaml. This document uses microservice.yaml to indicate the configuration file. You need to use a configuration file name corresponding to your project.

Procedure

Add dependencies to the pom.xml file of the project.
```
<dependency>
    <groupId>org.apache.servicecomb</groupId>
    <artifactId>solution-basic</artifactId>
</dependency>
<dependency>
    <groupId>org.apache.servicecomb</groupId>
    <artifactId>servicestage-environment</artifactId>
</dependency>
```
- The solution-basic module contains common Java chassis functions, such as the configuration center module and service governance module, which allow you to enable these functions in one-click.
```

<dependency>
<groupId>org.apache.servicecomb</groupId>
<artifactId>config-cc</artifactId>
</dependency>

<dependency>
<groupId>org.apache.servicecomb</groupId>
<artifactId>handler-governance</artifactId>
</dependency>
```
- The servicestage-environment module consists of the following dependent module:
```

<dependency>
  <groupId>org.apache.servicecomb</groupId>
  <artifactId>registry-service-center</artifactId>
</dependency>
```
You are advised to use Maven Dependency Management to manage the third-party software dependencies of a project. Add the following information to the pom.xml file of the project:
```
<dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.apache.servicecomb</groupId>
        <artifactId>java-chassis-dependencies</artifactId>
        <version>${java-chassis.version}</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>  
</dependencyManagement>
```
Skip the operation if your project already contains the preceding dependencies.

The servicestage-environment software package is optional. This software package provides the environment variable mapping function. When you use ServiceStage to deploy applications, you do not need to manually modify information such as the registry center address, configuration center address, and project name. The default configurations in the microservice.yaml file are overwritten by environment variables. The mapping.yaml file is contained in the software package. You can also add the mapping.yaml file to your own project.

The mapping.yaml file may change in later versions to support the latest functions of ServiceComb engines. If you do not want the new version to evolve with ServiceComb engines, you can add the mapping.yaml file to your project instead of adding the servicestage-environment dependency.

Generally, the microservice.yaml and mapping.yaml files are stored in the /src/main/resources/ directory in the root directory of the current project.
```
PAAS_CSE_ENDPOINT:
  - servicecomb.service.registry.address
  - servicecomb.config.client.serverUri
PAAS_CSE_SC_ENDPOINT:
  - servicecomb.service.registry.address
PAAS_CSE_CC_ENDPOINT:
  - servicecomb.config.client.serverUri
PAAS_PROJECT_NAME:
  - servicecomb.credentials.project

# CAS_APPLICATION_NAME:
#  - servicecomb.service.application
# CAS_COMPONENT_NAME:
#  - servicecomb.service.name
# CAS_INSTANCE_VERSION:
#  - servicecomb.service.version
```
Common software packages are added to solution-basic, and the default microservice.yaml file is provided. This configuration file configures common Handlers and parameters as follows:
```
# order of this configure file
servicecomb-config-order: -100

servicecomb:

# handlers
  handler:
    chain:
      Provider:
        default: qps-flowcontrol-provider
      Consumer:
        default: qps-flowcontrol-consumer,loadbalance,fault-injection-consumer

# loadbalance strategies
  references:
    version-rule: 0+
  loadbalance:
    retryEnabled: true
    retryOnNext: 1
    retryOnSame: 0

# metrics and access log
  accesslog:
    enabled: true
  metrics:
    window_time: 60000
    invocation:
      latencyDistribution: 0,1,10,100,1000
    Consumer.invocation.slow:
      enabled: true
      msTime: 1000
    Provider.invocation.slow:
      enabled: true
      msTime: 1000
    publisher.defaultLog:
      enabled: true
      endpoints.client.detail.enabled: true
```
servicecomb-config-order is set to -100 in the microservice.yaml configuration file, indicating that the priority of the configuration file is low. (A larger order indicates a higher priority. The default value is 0.) If the same configuration item is added to the service, the configuration will be overwritten.

The microservice.yaml file may change in later versions to support the latest functions of ServiceComb engines. If you do not want the new version to evolve with ServiceComb engines, you can write the configuration items to your own microservice.yaml file.
(Optional) Configure security authentication parameters.
Perform this step only when you use the exclusive ServiceComb engine and enable security authentication. In other scenarios, skip this step.

After security authentication is enabled for a ServiceComb engine, all called APIs can be called only after a token is obtained. For details about the authentication process, see RBAC.

To use security authentication, obtain the username and password from the ServiceComb engine and then add the following configuration to the configuration file.
```
servicecomb:
  credentials:
    rbac.enabled: true
    account:
      name: your account name # Username obtained from the ServiceComb engine
      password: your password # Password obtained from the ServiceComb engine
    cipher: default # Returned name of the name() method in the implementation class of API org.apache.servicecomb.foundation.auth.Cipher
```
cipher specifies the name of the algorithm used to encrypt the password. By default, the password is stored in plaintext. The encryption is implemented through customization. The details are as follows:
- Implement the org.apache.servicecomb.foundation.auth.Cipher API using either of the following methods:
  - String name()
    Name definition of servicecomb.credentials.cipher, which needs to be added to the configuration file.
  - char[] decode(char[] encrypted)
    Decrypt the API, which is used after secretKey is decrypted.
  The implementation class must be declared as SPI. For example:
```
package com.example
public class MyCipher implements Cipher
```
  Create an SPI configuration file. The file name and path are META-INF/service/org.apache.servicecomb.foundation.auth.Cipher, and the file content is as follows:
```
com.example.MyCipher
```
  Add the following configuration to the microservice.yaml file:
```
servicecomb:
  credentials:
    rbac.enabled: true
    account:
      name: your account name 
      password: your password # Encrypted password
    cipher: youciphername # Returned name of the name() method in the implementation class
```
Plaintext storage cannot ensure security. You are advised to encrypt the password.