前一陣子公司專案讓我有機會使用 Spring Boot 開發，但因為當時專案時間很趕，所以也一直專注在開發上當時開發所需要的技術。由於不熟 Spring Boot or Spring Core，所以用的東西都很基礎。所以我想趁現在好好的充實自己並嘗試寫一個 Spring Boot 系列的文章。
環境確認
這系列的文章，會以以下的版本為主
- Java 11
- Spring Boot 2.7
- Apache Maven 3.8.2
建立第一個 Hello World
由於艾倫以前已經使用過 IDE 或 網頁版的 Spring Boot Initializr 初始化，所以這次會以還未使用過的 Spring CLI。
安裝 Spring CLI
1$ brew tap spring-io/tap
2$ brew install springboot
3
4$ spring --version
5Spring CLI v2.7.0
使用 Spring CLI 初始化專案
1$ spring init -dweb -j 11 -v 1.0.0 -a helloworld
2Using service at https://start.spring.io
3Content saved to 'helloworld.zip'
這邊對參數做一些小解釋
- -d: 是 Dependencies，指定專案所需要的 packages，目前先選擇最基本的 web starter
- -j: 是 Java 版本，這邊我們選擇 Java 11
- -v: 此專案的版本初始化
- -a: 是 artifact Id
更多的參數或者 dependencies 的選擇，可以透過 spring init -list 看到。
執行 Spring Boot
建立一個新的資料夾如 demo，將剛剛 Spring CLI 所產生的 ZIP 檔案放入資料夾中，並解壓縮。 在 Terminal 中移動到那個 folder 並在裡面執行 “./mvnw spring-boot:run” ，最後可以看到以下畫面
1 . ____ _ __ _ _
2 /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
3( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
4 \\/ ___)| |_)| | | | | || (_| | ) ) ) )
5 ' |____| .__|_| |_|_| |_\__, | / / / /
6 =========|_|==============|___/=/_/_/_/
7 :: Spring Boot :: (v2.7.0)
8
92022-06-12 22:08:28.328 INFO 85059 --- [ main] com.example.helloworld.DemoApplication : Starting DemoApplication using Java 17 on ChangdeMacBook-Pro.local with PID 85059 (/Users/allen/helloworld/target/classes started by allen in /Users/allen/helloworld)
102022-06-12 22:08:28.331 INFO 85059 --- [ main] com.example.helloworld.DemoApplication : No active profile set, falling back to 1 default profile: "default"
112022-06-12 22:08:29.023 INFO 85059 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
122022-06-12 22:08:29.035 INFO 85059 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
132022-06-12 22:08:29.035 INFO 85059 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.63]
142022-06-12 22:08:29.107 INFO 85059 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
152022-06-12 22:08:29.107 INFO 85059 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 721 ms
162022-06-12 22:08:29.395 INFO 85059 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path ''
172022-06-12 22:08:29.404 INFO 85059 --- [ main] com.example.helloworld.DemoApplication : Started DemoApplication in 1.627 seconds (JVM running for 1.887)
從上面的訊息來看，可以看到 Spring Application 已經用 Tomcat 起來，且正在聽 8080 port。
這時我們嘗試打 8080 port
1 ~ curl http://127.0.0.
2{"timestamp":"2022-06-12T14:10:55.321+00:00","status":404,"error":"Not Found","path":"/"}
會得到 404 Error Msg，這是正常的，因為目前我們還沒有建立任何的 endpoint ～ 但至少確認 Tomcat 有起來。
Spring CLI 產生檔案
我們可以看到 Spring CLI 已經幫我們產生了以下的檔案
1$ tree
2.
3├── HELP.md
4├── mvnw
5├── mvnw.cmd
6├── pom.xml
7└── src
8 ├── main
9 │ ├── java
10 │ │ └── com
11 │ │ └── example
12 │ │ └── helloworld
13 │ │ └── DemoApplication.java
14 │ └── resources
15 │ ├── application.properties
16 │ ├── static
17 │ └── templates
18 └── test
19 └── java
20 └── com
21 └── example
22 └── helloworld
23 └── DemoApplicationTests.java
DemoApplication.java
我們可以看到 Spring Boot 的進入點 SpringApplication.run。
如果對 Spring Boot 啟動時做了什麼事情有興趣，可以看看這篇文章 從 SpringBootApplication 談談 Spring Boot 啓動時都做了哪些事？
1package com.example.helloworld;
2
3import org.springframework.boot.SpringApplication;
4import org.springframework.boot.autoconfigure.SpringBootApplication;
5
6@SpringBootApplication
7public class DemoApplication {
8
9 public static void main(String[] args) {
10 SpringApplication.run(DemoApplication.class, args);
11 }
12
13}
Pom.xml
1<?xml version="1.0" encoding="UTF-8"?>
2<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
4 <modelVersion>4.0.0</modelVersion>
5 <parent>
6 <groupId>org.springframework.boot</groupId>
7 <artifactId>spring-boot-starter-parent</artifactId>
8 <version>2.7.0</version>
9 <relativePath/> <!-- lookup parent from repository -->
10 </parent>
11 <groupId>com.example</groupId>
12 <artifactId>helloworld</artifactId>
13 <version>1.0.0</version>
14 <name>demo</name>
15 <description>Demo project for Spring Boot</description>
16 <properties>
17 <java.version>11</java.version>
18 </properties>
19 <dependencies>
20 <dependency>
21 <groupId>org.springframework.boot</groupId>
22 <artifactId>spring-boot-starter-web</artifactId>
23 </dependency>
24
25 <dependency>
26 <groupId>org.springframework.boot</groupId>
27 <artifactId>spring-boot-starter-test</artifactId>
28 <scope>test</scope>
29 </dependency>
30 </dependencies>
31
32 <build>
33 <plugins>
34 <plugin>
35 <groupId>org.springframework.boot</groupId>
36 <artifactId>spring-boot-maven-plugin</artifactId>
37 </plugin>
38 </plugins>
39 </build>
40
41</project>
從上面看到，我們繼承了 starter parent，且 dependencies 如預期裡面包含了 web starter 跟我們一開始初始化專案時所要求的一樣。
最後這邊可以看到，有裝 spring boot maven plugin，這是我們執行 mvn spring-boot:run 所需要的 plugin。
Maven dependency tree
當我們下 “./mvnw dependency:tree” 時，我們可以看到整個專案所需要的所包含的 package，也可以看到 package 中所拉到的其他 package 或者我們叫 transitive dependencies。
以下面的結果為範例，我們可以看到 spring-boot-starter-web 裡面有包含 spring-boot-starter-tomcat。
1$ ./mvnw dependency:tree
2[INFO] com.example:helloworld:jar:1.0.0
3[INFO] +- org.springframework.boot:spring-boot-starter-web:jar:2.7.0:compile
4[INFO] | +- org.springframework.boot:spring-boot-starter:jar:2.7.0:compile
5[INFO] | | +- org.springframework.boot:spring-boot:jar:2.7.0:compile
6[INFO] | | +- org.springframework.boot:spring-boot-autoconfigure:jar:2.7.0:compile
7[INFO] | | +- org.springframework.boot:spring-boot-starter-logging:jar:2.7.0:compile
8[INFO] | | | +- ch.qos.logback:logback-classic:jar:1.2.11:compile
9[INFO] | | | | \- ch.qos.logback:logback-core:jar:1.2.11:compile
10[INFO] | | | +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.17.2:compile
11[INFO] | | | | \- org.apache.logging.log4j:log4j-api:jar:2.17.2:compile
12[INFO] | | | \- org.slf4j:jul-to-slf4j:jar:1.7.36:compile
13[INFO] | | +- jakarta.annotation:jakarta.annotation-api🫙1.3.5:compile
14[INFO] | | \- org.yaml:snakeyaml:jar:1.30:compile
15[INFO] | +- org.springframework.boot:spring-boot-starter-json:jar:2.7.0:compile
16[INFO] | | +- com.fasterxml.jackson.core:jackson-databind:jar:2.13.3:compile
17[INFO] | | | +- com.fasterxml.jackson.core:jackson-annotations:jar:2.13.3:compile
18[INFO] | | | \- com.fasterxml.jackson.core:jackson-core:jar:2.13.3:compile
19[INFO] | | +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.13.3:compile
20[INFO] | | +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.13.3:compile
21[INFO] | | \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.13.3:compile
22[INFO] | +- org.springframework.boot:spring-boot-starter-tomcat:jar:2.7.0:compile
23[INFO] | | +- org.apache.tomcat.embed:tomcat-embed-core:jar:9.0.63:compile
24[INFO] | | +- org.apache.tomcat.embed:tomcat-embed-el:jar:9.0.63:compile
25[INFO] | | \- org.apache.tomcat.embed:tomcat-embed-websocket:jar:9.0.63:compile
26[INFO] | +- org.springframework:spring-web:jar:5.3.20:compile
27[INFO] | | \- org.springframework:spring-beans:jar:5.3.20:compile
28[INFO] | \- org.springframework:spring-webmvc:jar:5.3.20:compile
29[INFO] | +- org.springframework:spring-aop:jar:5.3.20:compile
30[INFO] | +- org.springframework:spring-context:jar:5.3.20:compile
31[INFO] | \- org.springframework:spring-expression:jar:5.3.20:compile
將 Tomcat 換成 Jetty
從 dependency tree 我們已經看到 tomcat 是由 web start 拉入的，所以我們可以透過 exclusion 將 tomcat starter 從 web starter 中排除，並手動拉入 jetty starter。
1<dependencies>
2 <dependency>
3 <groupId>org.springframework.boot</groupId>
4 <artifactId>spring-boot-starter-web</artifactId>
5 <exclusions>
6 <!-- 去除Tomcat容器 -->
7 <exclusion>
8 <groupId>org.springframework.boot</groupId>
9 <artifactId>spring-boot-starter-tomcat</artifactId>
10 </exclusion>
11 </exclusions>
12 </dependency>
13 <!-- 增加Jetty容器 -->
14 <dependency>
15 <groupId>org.springframework.boot</groupId>
16 <artifactId>spring-boot-starter-jetty</artifactId>
17 </dependency>
18 <dependency>
19 <groupId>org.springframework.boot</groupId>
20 <artifactId>spring-boot-starter-test</artifactId>
21 <scope>test</scope>
22 </dependency>
23</dependencies>
這時我們重新執行 ./mvnw spring-boot:run
1 . ____ _ __ _ _
2 /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
3( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
4 \\/ ___)| |_)| | | | | || (_| | ) ) ) )
5 ' |____| .__|_| |_|_| |_\__, | / / / /
6 =========|_|==============|___/=/_/_/_/
7 :: Spring Boot :: (v2.7.0)
8
92022-06-12 22:49:19.224 INFO 87278 --- [ main] com.example.helloworld.DemoApplication : Starting DemoApplication using Java 17 on ChangdeMacBook-Pro.local with PID 87278 (/Users/allen/helloworld/target/classes started by allen in /Users/allen/helloworld)
102022-06-12 22:49:19.226 INFO 87278 --- [ main] com.example.helloworld.DemoApplication : No active profile set, falling back to 1 default profile: "default"
112022-06-12 22:49:19.740 INFO 87278 --- [ main] org.eclipse.jetty.util.log : Logging initialized @1029ms to org.eclipse.jetty.util.log.Slf4jLog
122022-06-12 22:49:19.857 INFO 87278 --- [ main] o.s.b.w.e.j.JettyServletWebServerFactory : Server initialized with port: 8080
132022-06-12 22:49:19.860 INFO 87278 --- [ main] org.eclipse.jetty.server.Server : jetty-9.4.46.v20220331; built: 2022-03-31T16:38:08.030Z; git: bc17a0369a11ecf40bb92c839b9ef0a8ac50ea18; jvm 17+0
142022-06-12 22:49:19.896 INFO 87278 --- [ main] o.e.j.s.h.ContextHandler.application : Initializing Spring embedded WebApplicationContext
152022-06-12 22:49:19.897 INFO 87278 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 633 ms
162022-06-12 22:49:19.958 INFO 87278 --- [ main] org.eclipse.jetty.server.session : DefaultSessionIdManager workerName=node0
172022-06-12 22:49:19.958 INFO 87278 --- [ main] org.eclipse.jetty.server.session : No SessionScavenger set, using defaults
182022-06-12 22:49:19.959 INFO 87278 --- [ main] org.eclipse.jetty.server.session : node0 Scavenging every 600000ms
192022-06-12 22:49:19.966 INFO 87278 --- [ main] o.e.jetty.server.handler.ContextHandler : Started o.s.b.w.e.j.JettyEmbeddedWebAppContext@69da0b12{application,/,[file:///private/var/folders/dx/18qvmm_55hz74r3xdx9wn6x40000gn/T/jetty-docbase.8080.12428220257398218881/],AVAILABLE}
202022-06-12 22:49:19.966 INFO 87278 --- [ main] org.eclipse.jetty.server.Server : Started @1256ms
212022-06-12 22:49:20.187 INFO 87278 --- [ main] o.e.j.s.h.ContextHandler.application : Initializing Spring DispatcherServlet 'dispatcherServlet'
222022-06-12 22:49:20.187 INFO 87278 --- [ main] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
232022-06-12 22:49:20.188 INFO 87278 --- [ main] o.s.web.servlet.DispatcherServlet : Completed initialization in 1 ms
242022-06-12 22:49:20.219 INFO 87278 --- [ main] o.e.jetty.server.AbstractConnector : Started ServerConnector@17ca8b92{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
252022-06-12 22:49:20.220 INFO 87278 --- [ main] o.s.b.web.embedded.jetty.JettyWebServer : Jetty started on port(s) 8080 (http/1.1) with context path '/'
262022-06-12 22:49:20.230 INFO 87278 --- [ main] com.example.helloworld.DemoApplication : Started DemoApplication in 1.274 seconds (JVM running for 1.52)
我們可以看到 Application 現在由 Jetty 9.4 起來～
評論