Spring中@Import的三種情況

本文轉載自查看原文 2020-05-26 06:53 4112 Java/ Spring

我們在使用Spring框架中，特別是框架級的功能，經常看到有@Import導入功能，

我就介紹下它能導入什么，首先聲明下@Import是注解，導入類型可分為三類：

1. 導入配置 @Configuration，類似於spring早期版本2.5的import xml文件一樣，

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd "> <import resource="cms-validator-service.xml"/> <import resource="cms-validator-dao.xml"/> </beans>

只是現在注解搶了風頭，但目的一樣，用於使用所有標有@configuration注解的配置。

下面我就寫個小例子，怎么建java項目就略了

先建java主包com.spring, 然后分別建子包

com.spring.service,  com.spring.service.impl, com.spring.config, com.spring.test

1.1 建立服務接口

package com.spring.service; /** * * @author dgm * @describe "日志服務接口" */ public interface LogService { void print(String message); }

1.2 建立服務實現類，分三種情況，控制台、文件和數據庫mysql

package com.spring.service.impl; import org.springframework.stereotype.Component; import com.spring.service.LogService; /** * @author dgm * @describe "日志到控制台" */ @Component public class StdOutLogServiceImpl implements LogService { @Override public void print(String message) { System.out.println(message); System.out.println("寫日志到控制台！"); } } import java.io.File; import java.io.FileWriter; import java.io.IOException; import org.springframework.stereotype.Component; import com.spring.service.LogService; /** * * @author dgm * @describe "日志到文件" */ @Component public class FileLogServiceImpl implements LogService { private static final String FILE_NAME="d://LogService.txt"; @Override public void print(String message) { try { File file = new File(FILE_NAME); FileWriter fw = null; // true:表示是追加的標志 fw = new FileWriter(file, true); fw.write(message+"\n"); fw.close(); System.out.println(message); System.out.println("寫日志入文件！"); } catch (IOException e) { } } } /** * @author dgm * @describe "寫日志入mysql數據庫" */ @Component public class MysqlLogServiceImpl implements LogService { @Override public void print(String message) { System.out.println(message); System.out.println("寫日志入數據庫"); } }

1.3 寫配置類，三個服務實現類對應三個@Configuration

package com.spring.config; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import com.spring.service.LogService; import com.spring.service.impl.StdOutLogServiceImpl; @Configuration public class StdOutConfig { @Bean(name="stdOutLogServiceImpl") public LogService stdOutLogServiceImpl(){ return new StdOutLogServiceImpl(); } } import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import com.spring.service.LogService; import com.spring.service.impl.FileLogServiceImpl; @Configuration public class FileLogConfig { @Bean(name="fileLogServiceImpl") public LogService fileLogServiceImpl(){ return new FileLogServiceImpl(); } } import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import com.spring.service.LogService; import com.spring.service.impl.MysqlLogServiceImpl; @Configuration public class MysqlLogConfig { @Bean(name="mysqlLogServiceImpl") public LogService mysqlLogServiceImpl(){ return new MysqlLogServiceImpl(); } }

然后@Import注解登場了

import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; @Configuration @Import({StdOutConfig.class, FileLogConfig.class, MysqlLogConfig.class}) public class LogParentConfig { }

1.4 建立測試類看效果

import org.springframework.context.annotation.AnnotationConfigApplicationContext; import com.spring.config.LogParentConfig; import com.spring.service.*; /** * @author dgm * @describe "java configuration bean" */ public class LogConfigurationAppTest { public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext( LogParentConfig.class); //控制台 LogService obj = (LogService) context.getBean("stdOutLogServiceImpl"); System.out.println(obj); obj.print("控制台輸出"); //file obj = (LogService) context.getBean("fileLogServiceImpl"); System.out.println(obj); obj.print("文件輸出"); //mysql obj = (LogService) context.getBean("mysqlLogServiceImpl"); System.out.println(obj); obj.print("數據庫mysql"); context.close(); } }

輸出效果

2. 導入實現ImportSelector接口或子接口DeferredImportSelector的類

@Import annotation can also be configured with an ImportSelector implementation to select @Configuration classes programmatically, based on some selection criteria.

下面我也演示下，這個很重要，框架里和spring擴展開發用的多，先建立備用子包com.spring.bean和com.spring.importSelector，然后建立配置文件目錄conf

2.1 實現了ImportSelector

2.1.1 建立輔助類ApplicationProperties.java和外置配置文件myapp.properties

package com.spring.bean; public class ApplicationProperties { private String connectionUrl; private String connectionName; public String getConnectionUrl() { return connectionUrl; } public void setConnectionUrl(String connectionUrl) { this.connectionUrl = connectionUrl; } public String getConnectionName() { return connectionName; } public void setConnectionName(String connectionName) { this.connectionName = connectionName; } @Override public String toString() { return "ApplicationProperties [connectionUrl=" + connectionUrl + ", connectionName=" + connectionName + "]"; } }

然后在conf目錄下建立配置文件myapp.properties，內容如下：

app.url=https://github.com/dongguangming
app.name=dongguangming

2.1.2 建立@Configuration配置類

@Configuration @PropertySource("classpath:conf/myapp.properties") public class AppConfig { @Autowired ConfigurableEnvironment environment; @Bean ApplicationProperties appProperties() { ApplicationProperties bean = new ApplicationProperties(); bean.setConnectionUrl(environment.getProperty("app.url")); bean.setConnectionName(environment.getProperty("app.name")); return bean; } }

2.1.3 建立實現了ImportSelector接口的導入類，返回列表里的值是有標志@Configuration

public class LogImportSelector implements ImportSelector{ @Override public String[] selectImports(AnnotationMetadata importingClassMetadata) { return new String[]{"com.spring.config.AppConfig","com.spring.config.LogParentConfig"}; } }

2.1.4 建立有@import功能的配置類，導入2.1.3的實現類

package com.spring.config; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; import com.spring.importSelector.LogImportSelector; @Configuration @Import(LogImportSelector.class) public class LogImportSelectorConfig { }

2.1.5 編寫測試類

import org.springframework.context.annotation.AnnotationConfigApplicationContext; import com.spring.bean.ApplicationProperties; import com.spring.config.LogImportSelectorConfig; import com.spring.service.*; /** * @author dgm * @describe "java configuration bean" */ public class LogImportSelectorConfigurationAppTest { public static void main(String[] args) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext( LogImportSelectorConfig.class); // 控制台 LogService obj = (LogService) context.getBean("stdOutLogServiceImpl"); System.out.println(obj); obj.print("控制台輸出"); // file obj = (LogService) context.getBean("fileLogServiceImpl"); System.out.println(obj); obj.print("文件輸出"); // mysql obj = (LogService) context.getBean("mysqlLogServiceImpl"); System.out.println(obj); obj.print("數據庫mysql"); // ApplicationProperties ap = context.getBean(ApplicationProperties.class); System.out.println(ap); context.close(); } }

輸出效果：

效果不錯，也能完成bean的注冊

還有一種基於注解的變體，我也示例下，先建個子包com.spring.annotation

建立自定義注解：

@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(LogImportSelector.class) /** * @author dgm * @describe "自定義Enable功能" */ public @interface EnableLogService { //默認日志輸出到控制台 String logType() default "stdout"; @AliasFor("value") String[] basePackages() default {}; @AliasFor("basePackages") String[] value() default {}; }

然后修改導入選擇器實現類，根據啟用日志功能時傳的參數絕對加載哪個bean

AnnotationAttributes attributes = AnnotationAttributes
				.fromMap(importingClassMetadata.getAnnotationAttributes(
						EnableLogService.class.getName(), false)); System.out.println(attributes); //根據日志類型確定加載bean String logType = attributes.getString("logType"); if (logType.equalsIgnoreCase("StdOut")) { return new String[] { "com.spring.config.AppConfig", "com.spring.config.StdOutConfig" }; } else if (logType.equalsIgnoreCase("File")) { return new String[] { "com.spring.config.AppConfig", "com.spring.config.FileLogConfig" }; } else if (logType.equalsIgnoreCase("Mysql")) { return new String[] { "com.spring.config.AppConfig", "com.spring.config.MysqlLogConfig" }; } else { return new String[] { "com.spring.config.AppConfig", "com.spring.config.LogParentConfig" }; }

修改配置類，追加自定義注解@EnableLogService，並設置參數為file（可選stdout，file，mysql）

@Configuration //@Import(LogImportSelector.class) @EnableLogService(logType="file") public class LogImportSelectorConfig { }

修改測試類，此時不再是三種日志實現的bean都加載，按配置參數加載

LogService obj = (LogService) context.getBean("fileLogServiceImpl"); System.out.println(obj); obj.print("文件輸出");

就因為配置了@EnableLogService(logType="file")，只加載了一個日志實現bean

2.2 實現了 DeferredImportSelector

public interface DeferredImportSelector extends ImportSelector { }

可是看出它是2.1的子接口

The configuration class directly registered with the application context given preference over imported one. That means a bean of type T, configured in the main configuration will be used instead of a bean of the same type T from imported configuration. That applies to ImportSelector as well. On the other hand, DeferredImportSelector applies after all other configuration beans have been processed.

我們可以比較下實現兩種接口的區別

在主選擇器的配置類LogImportSelectorConfig.java中增加

@Bean LogBean logBean() { return new LogBean(); } @Bean(name = "fileLogServiceImpl") public LogService fileLogServiceImpl() { return new FileLogServiceImpl(" 來自LogImportSelectorConfig "); }

在文件配置類FileLogConfig.java中修改為

@Bean(name="fileLogServiceImpl") public LogService fileLogServiceImpl(){ return new FileLogServiceImpl("來自 FileLogConfig"); }

選擇器實現類還是

public class LogImportSelector implements ImportSelector {。。。}

執行測試代碼

LogBean bean = context.getBean(LogBean.class);
	    bean.printMessage();

此時修改選擇器實現的接口改為DeferredImportSelector，其它不改

public class LogImportSelector implements DeferredImportSelector {。。。}

再次執行測試

3 導入實現了ImportBeanDefinitionRegistrar接口的類

可以先瞄下接口的如何定義和定義了什么

public interface ImportBeanDefinitionRegistrar { public void registerBeanDefinitions( AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry); }

This Interface is to be implemented by types that register additional bean definitions when processing @Configuration classes.

具體可參考還記得我以前寫的博文Spring Bean注冊的幾種方式https://blog.csdn.net/dong19891210/article/details/105798650嗎，詳細看第5.2小節，這里就不再重復啰嗦寫了。

想了幾天還是花點時間寫上，畢竟放到個人電腦上不安全，我就一步一步開始完善

3.1 建立自定義組件注解標識和掃描包注解

@Documented @Indexed //@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER}) @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) /** * @author dgm * @describe "自定義組件注解標識" * @date 2020年5月27日 */ public @interface CustomComponent { String value() default ""; }

然后再建掃描包注解

@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Indexed @Import(CustomImportBeanDefinitionRegistrar.class) public @interface CustomComponentScan { @AliasFor("basePackages") String[] value() default {}; @AliasFor("value") String[] basePackages() default {}; Class<?>[] basePackageClasses() default {}; }

重點看@Import(CustomImportBeanDefinitionRegistrar.class)

3.2 定義實現了ImportBeanDefinitionRegistrar接口的類

public class CustomImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware { private ResourceLoader resourceLoader; @Autowired ConfigurableEnvironment environment; @Autowired ApplicationProperties applicationProperties; @Override public void registerBeanDefinitions( AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { AnnotationAttributes annotationAttributes = AnnotationAttributes .fromMap(importingClassMetadata.getAnnotationAttributes( CustomComponentScan.class.getName(), false)); //System.out.println(annotationAttributes); String[] basePackages = (String[]) annotationAttributes .get("basePackages"); System.err.println("要掃描的包是：" + Arrays.asList(basePackages)); if (basePackages == null || basePackages.length == 0) { String basePackage = null; try { basePackage = Class .forName(importingClassMetadata.getClassName()) .getPackage().getName(); } catch (ClassNotFoundException e) { e.printStackTrace(); } basePackages = new String[] { basePackage }; } MapperBeanDefinitionScanner scanner = new MapperBeanDefinitionScanner( registry, false); scanner.setResourceLoader(resourceLoader); // scanner.registerFilters(); scanner.addIncludeFilter(new AnnotationTypeFilter(CustomComponent.class)); scanner.doScan(basePackages); } @Override public void setResourceLoader(ResourceLoader resourceLoader) { this.resourceLoader = resourceLoader; } public class MapperBeanDefinitionScanner extends ClassPathBeanDefinitionScanner { public MapperBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) { super(registry, useDefaultFilters); } protected void registerFilters() { addIncludeFilter(new AnnotationTypeFilter(CustomComponent.class)); } @Override protected Set<BeanDefinitionHolder> doScan(String... basePackages) { return super.doScan(basePackages); } } }

3.3 定義配置類，預設組件掃描的包是com.spring.mapper

@Configuration @CustomComponentScan(basePackages= { "com.spring.mapper" }) public class CustomComponentConfiguration { }

3.4 建立自定義組件掃描的包com.spring.mapper,略

然后在自定義包下建立自定義組件，注意類上有自定義組件標識@CustomComponent

@CustomComponent public class CustomDataMapper { public List printData() throws SQLException { List<String> list = new ArrayList<>(); list.add("dongguangming"); list.add("張三"); list.add("李四"); return list; } }

3.5 編寫測試

/** * @author dgm * @describe "測試ImportBeanDefinitionRegistrar，自定義組件" */ public class CustomImportBeanDefinitionRegistrarTest { public static void main(String[] args) throws SQLException { //引入兩個配置類MysqlDatabaseConfiguration和CustomComponentConfiguration（由於MysqlDatabaseConfiguration關聯代碼多，所以沒有在文章里寫，測試時可去掉） AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext( MysqlDatabaseConfiguration.class, CustomComponentConfiguration.class); //就是我剛才自定義的組件類 CustomDataMapper data = applicationContext.getBean(CustomDataMapper); System.out.println(data); System.out.println(data.printData()); //從數據庫里查詢用戶列表 UserMapper userMapper = (UserMapper) applicationContext.getBean("userMapper"); System.out.println(userMapper); userMapper.queryMysql(); applicationContext.close(); } }