編寫Spring boot自動(dòng)配置

PAMPANG 發(fā)布于2019-08-16 14:22 / 2870人閱讀

摘要：背景學(xué)習(xí)的自動(dòng)配置對(duì)于了解整個(gè)后端代碼運(yùn)行流程非常重要只有在了解是如何配置的情況下才能在項(xiàng)目的配置中不那么舉步維艱假如我們編寫了一個(gè)用于處理文件信息的工具類那么我們可以如下操作工具步驟創(chuàng)建一個(gè)普通的項(xiàng)目注意其中的和這兩項(xiàng)將對(duì)應(yīng)以后使用的依賴

背景

學(xué)習(xí)spring boot的自動(dòng)配置對(duì)于了解整個(gè)后端代碼運(yùn)行流程非常重要,只有在了解spring boot是如何配置的情況下,才能在項(xiàng)目的配置中不那么舉步維艱.

START

假如我們編寫了一個(gè)用于處理文件信息的工具類,那么我們可以如下操作

工具

IntelliJ IDEA 2018

步驟

1.創(chuàng)建一個(gè)普通的spring boot項(xiàng)目

注意其中的Group和Artifact,這兩項(xiàng)將對(duì)應(yīng)以后使用的依賴參數(shù)


            xyz.crabapple
            begonia
            0.0.1-SNAPSHOT

2.項(xiàng)目的目錄結(jié)構(gòu)

3.現(xiàn)在我們主要代碼需要寫在begonia目錄下

4.代碼解釋

BegoniaApplication 為spring boot自己生成的入口類所在的java文件.

Tool 是我的工具類具體實(shí)現(xiàn)

public class Tool {
    public String prefix;
    public Tool(String prefix) {
        this.prefix = prefix;
    }
    /**
     * 計(jì)算時(shí)間戳
     * @return 時(shí)間戳+五位隨機(jī)大寫字母
     */
    public  String getStamp() {
        String prefix = String.valueOf(new Date().getTime());
        prefix=prefix.substring(2,prefix.length());
        char[] arr = new char[5];
        Random random = new Random();
        for (int i = 0; i < 5; i++)
            arr[i] = (char) (65 + random.nextInt(26));
        String Suffix = String.valueOf(arr);
        return prefix + Suffix;
    }

ToolProperties充當(dāng)配置類和application.properties的橋,即它從application.properties中取具體的配置信息,而真正的配置類需要再到ToolProperties去取.

@ConfigurationProperties(prefix = "Tool")
public class ToolProperties {
   private String prefix;

    public String getPrefix() {
        return prefix;
    }

    public void setPrefix(String path) {
        this.prefix = path;
    }
}

ToolAutoConfiguration是我的具體配置類

@Configuration
@EnableConfigurationProperties(ToolProperties.class)
@ConditionalOnClass(Tool.class)
@ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")
public class ToolAutoConfiguration {
    @Autowired
    ToolProperties toolProperties;
    @Bean
    public Tool autoConfiger(){
        System.out.println("Tool工具已啟動(dòng)");
        System.out.println(toolProperties.getPrefix());
        return new Tool(toolProperties.getPrefix());
    }
}

1.@Configuration 表示這是一個(gè)配置類,作用等同于@Component.
以下三個(gè)注解都是條件注解,如果有一個(gè)不滿足條件,自動(dòng)配置就不會(huì)運(yùn)行.
2.@EnableConfigurationProperties(ToolProperties.class)
表示配置類的自動(dòng)配置必須要求ToolProperties.class的存在
3.@ConditionalOnClass(Tool.class)
要求功能類存在.
4.@ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")
查看@ConditionOnProperty

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@Documented
@Conditional(OnPropertyCondition.class)
public @interface ConditionalOnProperty {

    /**
     * Alias for {@link #name()}.
     * @return the names
     */
    String[] value() default {};

    /**
     * A prefix that should be applied to each property. The prefix automatically ends
     * with a dot if not specified.
     * @return the prefix
     */
    String prefix() default "";

    /**
     * The name of the properties to test. If a prefix has been defined, it is applied to
     * compute the full key of each property. For instance if the prefix is
     * {@code app.config} and one value is {@code my-value}, the fully key would be
     * {@code app.config.my-value}
     * 
     * Use the dashed notation to specify each property, that is all lower case with a "-"
     * to separate words (e.g. {@code my-long-property}).
     * @return the names
     */
    String[] name() default {};

    /**
     * The string representation of the expected value for the properties. If not
     * specified, the property must not be equals to {@code false}.
     * @return the expected value
     */
    String havingValue() default "";

    /**
     * Specify if the condition should match if the property is not set. Defaults to
     * {@code false}.
     * @return if should match if the property is missing
     */
    boolean matchIfMissing() default false;

    /**
     * If relaxed names should be checked. Defaults to {@code true}.
     * @return if relaxed names are used
     */
    boolean relaxedNames() default true;

}

prefix和name拼湊起來(lái)表示application.properties的配置信息key,例如我的配置信息為Tool.open=true,那么@ConditionalOnProperty(prefix = "Tool", name="open" ,havingValue="true")就表示配置信息中有這個(gè)key就為true,即滿足條件,在此條件下若等于注解中havingValue的值,則該注解最終的結(jié)果為true.

最后我們需要注冊(cè)自己的配置類

在/src/main目錄下創(chuàng)建META-INF目錄,并其下創(chuàng)建spring.factories文件,其實(shí)spring.factories文件就是一個(gè).properties文件.

新建好后,在其中按如下方式書(shū)寫

org.springframework.boot.autoconfigure.EnableAutoConfiguration=
  xyz.crabapple.begonia.ToolAutoConfiguration

第一行的org.springframework.boot.autoconfigure.EnableAutoConfiguration就是一個(gè)key,第二行的xyz.crabapple.begonia.ToolAutoConfiguration就是我們的自動(dòng)配置類,即value.配置類還可以按需添加.例如我們找一個(gè)依賴看一看

找到一個(gè)spring boot自帶的依賴,可以看到其書(shū)寫方式,供大家參考.

# Initializers
org.springframework.context.ApplicationContextInitializer=
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,
org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer

END