一.Spring Boot Starter簡介
Starter是Spring Boot中的一個非常重要的概念，Starter相當于模塊，它能將模塊所需的依賴整合起來并對模塊內的Bean根據環境（ 條件）進行自動配置。使用者只需要依賴相應功能的Starter，無需做過多的配置和依賴，Spring Boot就能自動掃描并加載相應的模塊。
總結：
1.它整合了這個模塊需要的依賴庫；
2.提供對模塊的配置項給使用者；
3.提供自動配置類對模塊內的Bean進行自動裝配；
例如，在Maven的依賴中加入spring-boot-starter-web就能使項目支持Spring MVC，并且Spring Boot還為我們做了很多默認配置，無需再依賴spring-web、spring-webmvc等相關包及做相關配置就能夠立即使用起來。
二.Starter的開發步驟
編寫Starter非常簡單，與編寫一個普通的Spring Boot應用沒有太大區別，總結如下：
1.新建Maven項目，在項目的POM文件中定義使用的依賴；
2.新建配置類，寫好配置項和默認的配置值，指明配置項前綴；
3.新建自動裝配類，使用@Configuration和@Bean來進行自動裝配；
4.新建spring.factories文件，指定Starter的自動裝配類；
三.Starter的開發示例
下面，我就以創建一個自動配置并連接ElasticSearch的Starter來講一下各個步驟及細節。
1.新建Maven項目，在項目的POM文件中定義使用的依賴。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.4.RELEASE</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>es-starter</artifactId>
<version>1.0.0.SNAPSHORT</version>
<dependencies>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.18</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>2.0.4.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.elasticsearch.client</groupId>
<artifactId>x-pack-transport</artifactId>
<version>5.6.4</version>
</dependency>
</dependencies>
</project>
由于本starter主要是與ElasticSearch建立連接，獲得TransportClient對象，所以需要依賴
x-pack-transport包。
2.新建配置類，寫好配置項和默認的配置值，指明配置項前綴。
package cn.sxw.commons.data.es.starter;
import org.springframework.boot.context.properties.ConfigurationProperties;
import lombok.Data;
/**
* Created by William on 2018/8/7.
*/
@Data
@ConfigurationProperties(prefix = "sxw.elasticsearch")
public class ElasticSearchProperties {
private String clusterName = "elasticsearch";
private String clusterNodes = "127.0.0.1:9300";
private String userName = "elastic";
private String password = "changeme";
}
指定配置項前綴為
sxw.elasticsearch，各配置項均有默認值，默認值可以通過模塊使用者的配置文件進行覆蓋。
3.新建自動裝配類，使用@Configuration和@Bean來進行自動裝配。
package cn.sxw.commons.data.es.starter;
import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.InetSocketTransportAddress;
import org.elasticsearch.common.transport.TransportAddress;
import org.elasticsearch.xpack.client.PreBuiltXPackTransportClient;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
import java.util.stream.Collectors;
import javax.annotation.Resource;
import lombok.extern.slf4j.Slf4j;
/**
* Created by William on 2018/8/7.
*/
@Slf4j
@Configuration
@EnableConfigurationProperties(ElasticSearchProperties.class)
public class ElasticSearchAutoConfiguration implements DisposableBean{
private TransportClient transportClient;
@Resource
private ElasticSearchProperties properties;
@Bean
@ConditionalOnMissingBean(TransportClient.class)
public TransportClient transportClient() {
log.debug("=======" + properties.getClusterName());
log.debug("=======" + properties.getClusterNodes());
log.debug("=======" + properties.getUserName());
log.debug("=======" + properties.getPassword());
log.info("開始建立es連接");
transportClient = new PreBuiltXPackTransportClient(settings());
TransportAddress[] transportAddresses= Arrays.stream(properties.getClusterNodes().split(",")).map (t->{
String[] addressPortPairs = t.split(":");
String address = addressPortPairs[0];
Integer port = Integer.valueOf(addressPortPairs[1]);
try {
return new InetSocketTransportAddress(InetAddress.getByName(address), port);
} catch (UnknownHostException e) {
log.error("連接ElasticSearch失敗", e);
throw new RuntimeException ("連接ElasticSearch失敗",e);
}
}).collect (Collectors.toList ()).toArray (new TransportAddress[0]);
transportClient.addTransportAddresses(transportAddresses);
return transportClient;
}
private Settings settings() {
return Settings.builder()
.put("cluster.name", properties.getClusterName())
.put("xpack.security.user", properties.getUserName() +
":" + properties.getPassword())
.build();
}
@Override
public void destroy() throws Exception {
log.info("開始銷毀Es的連接");
if (transportClient != null) {
transportClient.close();
}
}
}
本類主要對TransportClient類進行自動配置;
@ConditionalOnMissingBean當Spring容器中沒有TransportClient類的對象時，調用transportClient()創建對象;
關于更多Bean的條件裝配用法請自行查閱Spring Boot相關文檔;
4.新建spring.factories文件，指定Starter的自動裝配類。
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
cn.sxw.commons.data.es.starter.ElasticSearchAutoConfiguration
spring.factories文件位于resources/META-INF目錄下，需要手動創建;
org.springframework.boot.autoconfigure.EnableAutoConfiguration后面的類名說明了自動裝配類，如果有多個 ，則用逗號分開;
使用者應用（SpringBoot）在啟動的時候，會通過org.springframework.core.io.support.SpringFactoriesLoader讀取classpath下每個Starter的spring.factories文件，加載自動裝配類進行Bean的自動裝配；
至此，整個Starter開發完畢，Deploy到中央倉庫或Install到本地倉庫后即可使用。
四.Starter的使用
1.創建Maven項目，依賴剛才發布的es-starter包。
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>spring-boot-parent</artifactId>
<groupId>org.springframework.boot</groupId>
<version>2.0.4.RELEASE</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>es-example</artifactId>
<version>1.0.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>es-starter</artifactId>
<version>1.0.0.SNAPSHORT</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
只需依賴剛才開發的es-starter即可
2.編寫應用程序啟動類。
package cn.sxw.commons.data.es.example;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
/**
* Created by William on 2018/8/7.
*/
@SpringBootApplication
@ComponentScan("cn.sxw.commons.data.es.example")
public class ExampleApplication {
public static void main(String[] args) {
SpringApplication.run(ExampleApplication.class, args);
}
}
@SpringBootApplication由@SpringBootConfiguration、@EnableAutoConfiguration、@ComponentScan三個注解組合而成，其中@EnableAutoConfiguration注解讓Spring Boot根據類路徑中的jar包依賴為當前項目進行自動配置。
3.編寫查詢ElasticSearch的使用類
package cn.sxw.commons.data.es.example;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.SearchHits;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;
import java.util.Map;
import lombok.extern.slf4j.Slf4j;
/**
* Created by William on 2018/8/7.
*/
@Slf4j
@Component
public class ExampleRunner implements ApplicationRunner {
private static final String INDEX_NAME = "tb_question";
@Autowired
private TransportClient transportClient;
@Override
public void run(ApplicationArguments applicationArguments) throws Exception {
SearchResponse response = transportClient.prepareSearch(INDEX_NAME)
.setTypes(INDEX_NAME)
.setQuery(QueryBuilders.matchAllQuery())
.setFrom(0).setSize(5).execute().actionGet();
SearchHits hits = response.getHits();
log.info(String.format("=======總共找到%d條記錄", hits.getTotalHits()));
log.info("=======第一頁數據：");
for (SearchHit searchHit : hits) {
Map<String, Object> source = searchHit.getSource();
String question = source.get("question").toString();
log.info(question);
}
}
}
通過實現ApplicationRunner或CommandLineRunner接口，可以實現應用程序啟動完成后自動運行run方法，達到測試es-starter模塊目的。
索引名稱tb_question是公司測試環境ElasticSearch中的索引，已存在數據。
4.應用程序配置
sxw:
elasticsearch:
cluster-name: docker-cluster
cluster-nodes: 192.168.2.180:9300,192.168.2.181:9300
user-name: elastic
password: changeme
在application.yml文件中配置es-starter需要的配置信息，這里連接公司測試環境中的ElasticSearch。
這里配置的值可以覆蓋es-starter中默認值，也就是之前ElasticSearchProperties文件中的默認值。
5.運行程序測試
/Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java "-javaagent:/Applications/開發/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=52434:/Applications/開發/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath cn.sxw.commons.data.es.example.ExampleApplication
objc[2017]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java (0x1022a24c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x1023254e0). One of the two will be used. Which one is undefined.
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.0.4.RELEASE)
2018-08-08 16:26:43.161 INFO 2017 --- [ main] c.s.c.d.es.example.ExampleApplication : Starting ExampleApplication on William.local with PID 2017 (/Users/William/Git/sxw-java/es-spring-boot-starter/es-example/target/classes started by William in /Users/William/Git/sxw-java/es-spring-boot-starter)
2018-08-08 16:26:43.167 INFO 2017 --- [ main] c.s.c.d.es.example.ExampleApplication : No active profile set, falling back to default profiles: default
2018-08-08 16:26:43.365 INFO 2017 --- [ main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@635eaaf1: startup date [Wed Aug 08 16:26:43 CST 2018]; root of context hierarchy
2018-08-08 16:26:45.078 INFO 2017 --- [ main] s.c.d.e.s.ElasticSearchAutoConfiguration : =======docker-cluster
2018-08-08 16:26:45.079 INFO 2017 --- [ main] s.c.d.e.s.ElasticSearchAutoConfiguration : =======192.168.2.180:9300,192.168.2.181:9300
2018-08-08 16:26:45.081 INFO 2017 --- [ main] s.c.d.e.s.ElasticSearchAutoConfiguration : =======elastic
2018-08-08 16:26:45.081 INFO 2017 --- [ main] s.c.d.e.s.ElasticSearchAutoConfiguration : =======changeme
2018-08-08 16:26:45.082 INFO 2017 --- [ main] s.c.d.e.s.ElasticSearchAutoConfiguration : 開始建立es連接
2018-08-08 16:26:46.200 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : no modules loaded
2018-08-08 16:26:46.201 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.index.reindex.ReindexPlugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.join.ParentJoinPlugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.percolator.PercolatorPlugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.script.mustache.MustachePlugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.transport.Netty3Plugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.transport.Netty4Plugin]
2018-08-08 16:26:46.202 INFO 2017 --- [ main] o.elasticsearch.plugins.PluginsService : loaded plugin [org.elasticsearch.xpack.XPackPlugin]
2018-08-08 16:26:49.137 INFO 2017 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2018-08-08 16:26:49.157 INFO 2017 --- [ main] c.s.c.d.es.example.ExampleApplication : Started ExampleApplication in 6.6 seconds (JVM running for 7.915)
2018-08-08 16:26:49.215 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : =======總共找到907條記錄
2018-08-08 16:26:49.215 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : =======第一頁數據：
2018-08-08 16:26:49.230 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : <p>下列詩句朗讀節奏有錯誤的一項是( )</p>
2018-08-08 16:26:49.230 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : <p><span style=";font-family:宋體;color:rgb(0,0,0);font-size:14px"><span style="font-family:宋體">《臥薪嘗膽》這個故事出自于（</span> A <span style="font-family:宋體">）</span></span></p><p><span style=";font-family:宋體;color:rgb(0,0,0);font-size:14px">A<span style="font-family:宋體">、司馬遷《史記》 </span><span style="font-family:Times New Roman">B</span><span style="font-family:宋體">、司馬光 《資治通鑒》</span></span></p><p><span style=";font-family:宋體;color:rgb(0,0,0);font-size:14px">C<span style="font-family:宋體">、孔子 《論語》 </span><span style="font-family:Times New Roman">D</span><span style="font-family:宋體">、司馬遷《春秋》</span></span></p><p><br/></p>
2018-08-08 16:26:49.230 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : <p style="margin-bottom:7px;margin-bottom:auto;vertical-align:middle"><span style=";font-family:'Cambria Math';font-size:14pxfont-family:宋體,新宋體">填空題</span></p><p style="margin-bottom:7px;margin-bottom:auto;vertical-align:middle"><span style=";font-family:'Cambria Math';font-size:14pxfont-family:宋體,新宋體">該模式給當地帶來的主要影響是 </span><span style=";font-family:'Cambria Math';font-size:14px"><br/></span><br/></p><p><br/></p>
2018-08-08 16:26:49.231 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : <p>下列詞語沒有錯別字的一項是( )</p>
2018-08-08 16:26:49.231 INFO 2017 --- [ main] c.s.c.data.es.example.ExampleRunner : <p>語文第16題</p>
2018-08-08 16:26:49.232 INFO 2017 --- [ Thread-2] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@635eaaf1: startup date [Wed Aug 08 16:26:43 CST 2018]; root of context hierarchy
2018-08-08 16:26:49.234 INFO 2017 --- [ Thread-2] o.s.j.e.a.AnnotationMBeanExporter : Unregistering JMX-exposed beans on shutdown
2018-08-08 16:26:49.328 INFO 2017 --- [ Thread-2] s.c.d.e.s.ElasticSearchAutoConfiguration : 開始銷毀Es的連接
Process finished with exit code 0
運行程序，觀察控制臺輸出，es-starter成功與ElasticSearch建立連接，且應用程序啟動完后ExampleRunner的run方法查詢出5條數據。
源代碼參考提供：
從零開始開發一個Spring Boot Starter
