Spring Boot学习--1 开始

1. 核心

Spring Boot 核心是入口类和@SpringBootApplication。入口类的名称是artifactId+Application，@SpringBootApplication注解是一个组合注解，主要MetaAnnotation为@Configuration和@EnableAutoConfiguration，以及@ComponentScan。其中@EnableAutoConfiguration让Spring Boot根据类路径中的jar包依赖为当前项目自动配置。

2. 配置文件

Spring Boot 的配置文件形式为application.properties或application.yml，后一种文件格式的后缀全称是yet another mark language。配置文件位于src/main/resources（如果是maven形式）下。
.properteis形式：

server.port=9009
server.servlet.context-path=/hello

.yml形式：

server:
    port: 9009
    servlet:
        context-path: /hello

spring boot 的properties设置参考：
https://docs.spring.io/spring-boot/docs/current/reference/html/common-application-properties.html。application.properties和application.yml中的属性可对属性的默认值进行覆盖，并可添加新的属性值对。

3. stater pom

采用Spring Tool Suit 或直接使用https://start.spring.io创建项目会自动建立一个start pom。创建一个基于web的项目，pom内容示例如下：

<?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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>com-springboot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>com-springboot</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

其中parent子元素spring-boot-starter-parent（artifactId）申明包含了多个jar包，通过@SpringBootApplication注解的@EnableAutoConfiguration注解，可对各个jar包中的Bean进行自动配置。

除了官方的start pom外，还有第三方为Spring Boot编写的pom文件。在pom形式之外，还可以通过在类上添加@ImportSource注解来加载xml配置文件。如：
@ImportSource({“classpath:contextA.xml”, “classpath:contextB.xml”})
public class DemoClass {
@Inject
//注入contextA.xml，contextB.xml配置的类
}

4. 属性使用方法

无论是application.properties还是自建的properties文件中属性值对，都可以采用两种方法进行使用。
第一种：
在field上使用@Value(“${属性名}”)注入，形式与Spring中注入形式相同。
第二种：
通过类型安全配置，即新建一个属性名称与配置文件属性名称一致的关联类(A)，在该类上用@ConfigurationProperties注解，再在需要使用属性的类（B）上用@EnableConfigurationProperties(A类.class)在Container中注册关联类，最后在使用属性的类中用@Autowired注入关联类的Bean。示例如下：

a. application.properties和自定义属性配置文件

application.properties：

book.name=springboot
book.author=cruise

自定义属性文件，位置为config/cruise.properties:

cruise.name=apple
cruise.address=The first street.

b .类型安全的Bean

通过application.properties配置的Bean：

package com.example.configproperty;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix="book") //使用配置文件中前缀为book的属性
public class BookSetting {
    private String name;
    private String author;

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

通过自定义properties文件配置的Bean：

package com.example.configproperty;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix="cruise")
public class CruiseSetting {
    private String name;
    private String address;

    public String getAddress() {
        return address;
    }

    public String getName() {
        return name;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public void setName(String name) {
        this.name = name;
    }
}

c. 使用属性的类

该类对直接使用application.properties和自定义配置文件，以及使用类型安全的Bean等多种属性使用方式进行了测试。

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.PropertySource;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.example.configproperty.BookSetting;
import com.example.configproperty.CruiseSetting;

//使用非applicaiton.properties的配置文件需要什么位置
@PropertySource("classpath:/config/cruise.properties")
//向容器注册类型安全配置的类，自此这些类可以用于注入
@EnableConfigurationProperties(value = {BookSetting.class, CruiseSetting.class})
@RestController
@SpringBootApplication
public class ComSpringbootApplication {

    // 直接使用application.properties
    @Value(value = "${book.name}")
    private String bookName;

    @Value("${book.author}")
    private String bookAuthor;

    //使用自定义properties文件
    @Value("${cruise.name}")
    private String cruiseName;

    @Value("${cruise.address}")
    private String cruiseAddress;

    //注入通过application.properties文件使用类型安全配置的Bean
    @Autowired
    private BookSetting bookSetting;

    //注入通过自定义properties文件使用类型安全配置的Bean
    @Autowired
    private CruiseSetting cruiseSetting;

    @RequestMapping(value = {"/index", "/"})
    public String index() {
        return "Use properties Directly from application.properties: book name is " + bookName 
                    + ", and book author is " + bookAuthor + "<br/>"
                    + "Use properties from Self definition properties file: cruise name is " + cruiseSetting.getName() 
                    + ", and cruise address is " + cruiseSetting.getAddress() + "<br/>"
                    + "Use properties from application.properties with Bean: book name is " + bookSetting.getName() 
                    + ", and book author is " + bookSetting.getAuthor() + "<br/>"
                    + "Use properties from Self definition properties file with Bean: cruise name is " + cruiseSetting.getName() 
                    + ", and cruise address is " + cruiseSetting.getAddress();
    }

    public static void main(String[] args) {
        SpringApplication.run(ComSpringbootApplication.class, args);
    }
}

5. 测试结果

浏览器显示：
Use properties Directly from application.properties: book name is springboot, and book author is cruise
Use properties from Self definition properties file: cruise name is apple, and cruise address is The first street.
Use properties from application.properties with Bean: book name is springboot, and book author is cruise
Use properties from Self definition properties file with Bean: cruise name is apple, and cruise address is The first street.