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.

Configure microservice information.

Add microservice configuration description to the microservice.yaml file. If there is no microservice.yaml file in the project, create one.

servicecomb:
  service:
    application: porter-application
    name: user-service
    version: 0.0.1
    registry:
      address: http://localhost:30100
      instance:
        watch: true
        properties:
          key: value
        initialStatus: UP
  config:
    client:
      serverUri: http://localhost:30103
      fileSource: provider.yaml
      firstPullRequired: false
      refresh_interval: 15000
      domainName: default
  kie: 
    serverUri: http://127.0.0.1:30110
    domainName: default
    enableLongPolling: true
    pollingWaitTime: 10
    firstPullRequired: false
    customLabel: public 
    customLabelValue: default

For the description of each configuration item, see Table 1.

**Table 1** Java chassis configuration items
Item	Description	Default Value	Mandatory	Remarks
servicecomb.service.application	Name of the application to which the current microservice belongs.	default	Yes	Only microservices with the same application name can discover each other.
servicecomb.service.name	Microservice name.	-	Yes	-
servicecomb.service.version	Service version.	1.0.0.0	Yes	This parameter is required during service upgrade to prevent contract registry failures.
servicecomb.service.registry.address	Registry address.	-	Yes	-
servicecomb.service.registry.instance.watch	Whether to listen to microservice startup and shutdown.	true	No	Use commas (,) to separate cluster addresses.
servicecomb.service.registry.instance.properties	Microservice instance property.	-	No	The value is in the map structure. Multiple groups of data can be set.
servicecomb.service.registry.instance.initialStatus	Status when a microservice is registered.	UP	No	Value: UP or DOWN.
servicecomb.config.client.serverUri	Access address. The format is http(s)://{ip}:{port}. Use commas (,) to separate multiple addresses.	-	Yes	This configuration is applicable when the configuration center is config-center. For ServiceComb engine 1.x, {port} is 30103. For ServiceComb engine 2.x, {port} is 30110.
servicecomb.config.client.fileSource	List of YAML configuration items, which are separated by commas (,)	-	No	When the configuration center type is config-center, if the configuration center delivers configurations through a configuration file, you must set fileSource to parse the configurations. Otherwise, the correct configurations cannot be obtained.
servicecomb.config.client.firstPullRequired	Whether the first pull configuration is forcibly successful. If the value is true, an exception is thrown after the first connection to the configuration center fails, and the service fails to be started. The default value is false.	-	No	This configuration is applicable when the configuration center is config-center.
servicecomb.config.client.refresh_interval	Cycle time for config-center to obtain configurations, in milliseconds.	15000	No	This configuration is applicable when the configuration center is config-center.
servicecomb.config.client.domainName	Project name.	default	No	This configuration is applicable when the configuration center is config-center.
servicecomb.kie.serverUri	Access address. The format is http(s)://{ip}:{port}. Use commas (,) to separate multiple addresses.	-	Yes	This configuration is applicable when the configuration center is kie. For ServiceComb engine 1.x, {port} is 30103. For ServiceComb engine 2.x, {port} is 30110.
servicecomb.kie.domainName	Project name.	-	No	This configuration is applicable when the configuration center is kie.
servicecomb.kie.enableLongPolling	Whether to enable the long connection pull configuration.	true	No	This configuration is applicable when the configuration center is kie.
servicecomb.kie.pollingWaitTime	Waiting duration of a long connection, in seconds.	10	No	This configuration is applicable when the configuration center is kie.
servicecomb.kie.firstPullRequired	Whether the first pull configuration is forcibly successful. If the value is true, an exception is thrown after the first connection to the configuration center fails, and the service fails to be started. The default value is false.	-	No	This configuration is applicable when the configuration center is kie.
servicecomb.kie.customLabel	Custom label.	-	No	When the configuration center is kie, if a custom label is used to deliver configurations, you need to configure customLabel and customLabelValue. The microservice name, environment name, and application name labels support only independent adaptation.
servicecomb.kie.customLabelValue	Custom label value.	-	No	-

(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.