這篇文章帶給大家的內容是關於Spring Boot中的條件判斷的介紹(附程式碼),有一定的參考價值,有需要的朋友可以參考一下,希望對你有幫助。
Spring Boot中的那些Conditional
spring boot中為我們提供了豐富的Conditional來讓我們得以非常方便的在專案中向容器中添加Bean。本文主要是將各個註解解釋並輔以程式碼說明其用途。
所有ConditionalOnXXX的註解都可以放置在class或是method上,如果方式在class上,則會決定該class中所有的@Bean註解方法是否執行。
下面其他的Conditional註解都是語法糖,可以透過下面的方法自訂ConditionalOnXXX
Conditional註解定義如下,接收實作Condition介面的class陣列。
public @interface Conditional { Class extends Condition>[] value(); }
而Condition介面只有一個matchs方法,傳回是否符合的結果。
public interface Condition { boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata); }
透過作業系統進行條件判斷,從而進行Bean配置。當Window時,實例化Bill的Person對象,當Linux時,實例化Linus的Person物件。
//LinuxCondition,为方便起见,去掉判断代码,直接返回true了 public class LinuxCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) { return true; } }
//WindowsCondition,为方便起见,去掉判断代码,直接返回false了 public class WindowsCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata metadata) { return false; } }
@Data @ToString @AllArgsConstructor @NoArgsConstructor public class Person { private String name; private Integer age; }
//配置类 @Configuration public class BeanConfig { @Bean(name = "bill") @Conditional({WindowsCondition.class}) public Person person1(){ return new Person("Bill Gates",62); } @Bean("linus") @Conditional({LinuxCondition.class}) public Person person2(){ return new Person("Linus",48); } }
public class AppTest { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ String osName = applicationContext.getEnvironment().getProperty("os.name"); System.out.println("当前系统为:" + osName); Map<string> map = applicationContext.getBeansOfType(Person.class); System.out.println(map); } }</string>
輸出的結果:
目前系統為:Mac OS X
{linus=Person(name=Linus, age=48)}
這兩個註解會對Bean容器中的Bean物件進行判斷,使用的例子是設定的時候,如果發現如果沒有Computer實例,則實例化一個備用電腦。
@Data @AllArgsConstructor @ToString public class Computer { private String name; }
@Configuration public class BeanConfig { @Bean(name = "notebookPC") public Computer computer1(){ return new Computer("笔记本电脑"); } @ConditionalOnMissingBean(Computer.class) @Bean("reservePC") public Computer computer2(){ return new Computer("备用电脑"); } }
public class TestApp { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test1(){ Map<string> map = applicationContext.getBeansOfType(Computer.class); System.out.println(map); } }</string>
修改BeanConfig,如果註解掉第一個@Bean,會實例化備用電腦,否則就不會實例化備用電腦
這個註解會判斷類路徑上是否有指定的類,一開始看到的時候比較困惑,類路徑上如果沒有指定的class,那編譯也通過不了啊...這個主要用於集成相同功能的第三方元件時用,只要類別路徑上有該元件的類別,就進行自動配置,例如spring boot web在自動配置視圖元件時,是用Velocity,還是Thymeleaf,或是freemaker時,使用的就是這種方式。
例子是兩組盔甲A(光明套裝)和B(暗黑套裝),如果A不在則配置B。
public interface Fighter { void fight(); } public class FighterA implements Fighter { @Override public void fight() { System.out.println("使用光明套装"); } } public class FighterB implements Fighter { @Override public void fight() { System.out.println("使用暗黑套装"); } }
Van是武士,使用套裝進行戰鬥
@Data @AllArgsConstructor @NoArgsConstructor public class Van { private Fighter fighter; public void fight(){ fighter.fight(); } }
VanConfigA/B實例化武士
@Configuration @ConditionalOnClass({FighterA.class}) public class VanConfigA { @Primary @Bean public Van vanA(){ return new Van(new FighterA()); } } @Configuration @ConditionalOnClass({FighterB.class}) public class VanConfigB { @Bean public Van vanB(){ return new Van(new FighterB()); } }
測試類別,預設情況,如果套裝AB都在類別路徑上,兩套都會載入,A會設定為PRIMARY,如果在target class中將FightA.class刪除,則只會載入套裝B。
@SpringBootApplication public class TestApp implements CommandLineRunner { @Autowired private Van van; public static void main(String[] args) { SpringApplication.run(TestApp.class, args); } @Override public void run(String... args) throws Exception { //do something van.fight(); } }
另外,試著將兩個VanConfigA/B合併,將註解ConditionalOnClass放到方法上,如果刪除一個套裝就會執行出錯。
依據表達式進行條件判斷,這個作用和@ConditionalOnProperty大部分情況可以通用,表達式更靈活一點,因為可以使用SpEL。例子中會判斷properties中test.enabled的值進行判斷。 BeanConfig分別對布爾,字串和數字三種類型進行判斷。數字嘗試了許多其他的方式不行,例如直接使用==,似乎配置的屬性都會當成字串來處理。
@Data public class TestBean { private String name; }
@Configuration @ConditionalOnExpression("#{${test.enabled:true} }") //@ConditionalOnExpression("'zz'.equalsIgnoreCase('${test.name2}')") //@ConditionalOnExpression("new Integer('${test.account}')==1") public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean("我是美猴王"); } }
@SpringBootApplication public class TestAppCommand implements CommandLineRunner { @Autowired private TestBean testBean; public static void main(String[] args) { SpringApplication.run(TestAppCommand.class, args); } @Override public void run(String... args) throws Exception { System.out.println(testBean.getName()); } }
適合對單一Property進行條件判斷,而上面的@ConditionalOnExpress適合面對較為複雜的情況,例如多個property的關聯比較。這個例子也給了三種基本類型的條件判斷,不過貌似均當成字串就可以...
@Data @AllArgsConstructor @NoArgsConstructor public class TestBean { private String name; }
@Configuration @ConditionalOnProperty(prefix = "test", name="enabled", havingValue = "true",matchIfMissing = false) //@ConditionalOnProperty(prefix = "test", name="account", havingValue = "1",matchIfMissing = false) //@ConditionalOnProperty(prefix = "test", name="name1", havingValue = "zz",matchIfMissing = false) public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean("我是美猴王"); } }
@SpringBootApplication public class TestAppCommand implements CommandLineRunner { @Autowired private TestBean testBean; public static void main(String[] args) { SpringApplication.run(TestAppCommand.class, args); } @Override public void run(String... args) throws Exception { System.out.println(testBean.getName()); } }
可以透過java的版本來判斷。
@Data public class TestBean { }
@Configuration @ConditionalOnJava(JavaVersion.EIGHT) public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(TestBean.class); System.out.println(map); } }</string>
透過指定的資源檔案是否存在進行條件判斷,例如判斷ehcache.properties來決定是否自動組裝ehcache元件。
@Data public class TestBean { }
@Configuration @ConditionalOnResource(resources = "classpath:application.yml") public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(TestBean.class); System.out.println(map); } }</string>
這個還沒想到應用場景,條件通過的條件是:1 對應的bean容器中只有一個2.對應的bean有多個,但是已經制定了PRIMARY 。範例中,BeanB組裝的時候需要看BeanA的組裝狀況,所以BeanBConfig要排在BeanAConfig之後.可以修改BeanAConfig,將@Primary註解去掉,或者把三個@Bean註解去掉,BeanB就不會實例化了。
@Data @AllArgsConstructor @NoArgsConstructor public class BeanA { private String name; }
@Configuration public class BeanAConfig { @Bean @Primary public BeanA bean1(){ return new BeanA("bean1"); } @Bean(autowireCandidate = false) public BeanA bean2(){ return new BeanA("bean2"); } //@Bean(autowireCandidate = false) public BeanA bean3(){ return new BeanA("bean3"); } }
@Data public class BeanB { }
@Configuration @AutoConfigureAfter(BeanAConfig.class) @ConditionalOnSingleCandidate(BeanA.class) public class BeanBConfig { @Bean public BeanB targetBean(){ return new BeanB(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanAConfig.class, BeanBConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(BeanA.class); System.out.println(map); Map<string> map2 = context.getBeansOfType(BeanB.class); System.out.println(map2); } }</string></string>
判斷目前環境是否為Web應用程式。
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public @interface Conditional { Class extends Condition>[] value(); }
public interface Condition { boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata); }
//LinuxCondition,为方便起见,去掉判断代码,直接返回true了 public class LinuxCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) { return true; } }
//WindowsCondition,为方便起见,去掉判断代码,直接返回false了 public class WindowsCondition implements Condition { @Override public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata metadata) { return false; } }
@Data @ToString @AllArgsConstructor @NoArgsConstructor public class Person { private String name; private Integer age; }
//配置类 @Configuration public class BeanConfig { @Bean(name = "bill") @Conditional({WindowsCondition.class}) public Person person1(){ return new Person("Bill Gates",62); } @Bean("linus") @Conditional({LinuxCondition.class}) public Person person2(){ return new Person("Linus",48); } }
public class AppTest { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ String osName = applicationContext.getEnvironment().getProperty("os.name"); System.out.println("当前系统为:" + osName); Map<string> map = applicationContext.getBeansOfType(Person.class); System.out.println(map); } }</string>
@Data @AllArgsConstructor @ToString public class Computer { private String name; }
@Configuration public class BeanConfig { @Bean(name = "notebookPC") public Computer computer1(){ return new Computer("笔记本电脑"); } @ConditionalOnMissingBean(Computer.class) @Bean("reservePC") public Computer computer2(){ return new Computer("备用电脑"); } }
public class TestApp { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test1(){ Map<string> map = applicationContext.getBeansOfType(Computer.class); System.out.println(map); } }</string>
public interface Fighter { void fight(); } public class FighterA implements Fighter { @Override public void fight() { System.out.println("使用光明套装"); } } public class FighterB implements Fighter { @Override public void fight() { System.out.println("使用暗黑套装"); } }
@Data @AllArgsConstructor @NoArgsConstructor public class Van { private Fighter fighter; public void fight(){ fighter.fight(); } }
@Configuration @ConditionalOnClass({FighterA.class}) public class VanConfigA { @Primary @Bean public Van vanA(){ return new Van(new FighterA()); } } @Configuration @ConditionalOnClass({FighterB.class}) public class VanConfigB { @Bean public Van vanB(){ return new Van(new FighterB()); } }
@SpringBootApplication public class TestApp implements CommandLineRunner { @Autowired private Van van; public static void main(String[] args) { SpringApplication.run(TestApp.class, args); } @Override public void run(String... args) throws Exception { //do something van.fight(); } }
@Data public class TestBean { private String name; }
@Configuration @ConditionalOnExpression("#{${test.enabled:true} }") //@ConditionalOnExpression("'zz'.equalsIgnoreCase('${test.name2}')") //@ConditionalOnExpression("new Integer('${test.account}')==1") public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean("我是美猴王"); } }
@SpringBootApplication public class TestAppCommand implements CommandLineRunner { @Autowired private TestBean testBean; public static void main(String[] args) { SpringApplication.run(TestAppCommand.class, args); } @Override public void run(String... args) throws Exception { System.out.println(testBean.getName()); } }
@Data @AllArgsConstructor @NoArgsConstructor public class TestBean { private String name; }
@Configuration @ConditionalOnProperty(prefix = "test", name="enabled", havingValue = "true",matchIfMissing = false) //@ConditionalOnProperty(prefix = "test", name="account", havingValue = "1",matchIfMissing = false) //@ConditionalOnProperty(prefix = "test", name="name1", havingValue = "zz",matchIfMissing = false) public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean("我是美猴王"); } }
@SpringBootApplication public class TestAppCommand implements CommandLineRunner { @Autowired private TestBean testBean; public static void main(String[] args) { SpringApplication.run(TestAppCommand.class, args); } @Override public void run(String... args) throws Exception { System.out.println(testBean.getName()); } }
@Data public class TestBean { }
@Configuration @ConditionalOnJava(JavaVersion.EIGHT) public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(TestBean.class); System.out.println(map); } }</string>
@Data public class TestBean { }
@Configuration @ConditionalOnResource(resources = "classpath:application.yml") public class BeanConfig { @Bean public TestBean testBean(){ return new TestBean(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(TestBean.class); System.out.println(map); } }</string>
这个还没有想到应用场景,条件通过的条件是:1 对应的bean容器中只有一个 2.对应的bean有多个,但是已经制定了PRIMARY。例子中,BeanB装配的时候需要看BeanA的装配情况,所以BeanBConfig要排在BeanAConfig之后.可以修改BeanAConfig,将@Primary注解去掉,或者把三个@Bean注解去掉,BeanB就不会实例化了。
@Data @AllArgsConstructor @NoArgsConstructor public class BeanA { private String name; }
@Configuration public class BeanAConfig { @Bean @Primary public BeanA bean1(){ return new BeanA("bean1"); } @Bean(autowireCandidate = false) public BeanA bean2(){ return new BeanA("bean2"); } //@Bean(autowireCandidate = false) public BeanA bean3(){ return new BeanA("bean3"); } }
@Data public class BeanB { }
@Configuration @AutoConfigureAfter(BeanAConfig.class) @ConditionalOnSingleCandidate(BeanA.class) public class BeanBConfig { @Bean public BeanB targetBean(){ return new BeanB(); } }
public class TestApp { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BeanAConfig.class, BeanBConfig.class); @Test public void test(){ Map<string> map = context.getBeansOfType(BeanA.class); System.out.println(map); Map<string> map2 = context.getBeansOfType(BeanB.class); System.out.println(map2); } }</string></string>
判断当前环境是否是Web应用。
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