Introduction to conditional judgment in Spring Boot (with code)

This article brings you an introduction to conditional judgment in Spring Boot (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Those Conditionals in Spring Boot

spring boot provides us with a rich set of Conditionals that allow us to add beans to the container in the project very conveniently. This article mainly explains each annotation and illustrates its use with code.

All ConditionalOnXXX annotations can be placed on class or method. If the method is on class, it will determine whether all @Bean annotated methods in the class are executed.

@Conditional

The other Conditional annotations below are all syntactic sugar. You can customize ConditionalOnXXX through the following method.
The Conditional annotation is defined as follows and receives the class array that implements the Condition interface.

public @interface Conditional {
    Class extends Condition>[] value();
}

The Condition interface has only one matches method, which returns the result of matching.

public interface Condition {
    boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}

Configure conditions through the operating system to configure Bean. When Window is used, Bill's Person object is instantiated, and when Linux is used, Linus' Person object is instantiated.

//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>

Output results:

The current system is: Mac OS X
{linus=Person(name=Linus, age=48)}

@ConditionalOnBean & @ ConditionalOnMissingBean

These two annotations will judge the Bean object in the Bean container. The example used is during configuration. If it is found that there is no Computer instance, a backup computer will be instantiated.

@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>

Modify BeanConfig, if you comment out the first @Bean, the backup computer will be instantiated, otherwise the backup computer will not be instantiated

@ConditionalOnClass & @ConditionalOnMissingClass

This annotation will determine whether there is a specified class on the class path. It was confusing when I first saw it. If there is no specified class on the class path, the compilation will not pass... This is mainly used to integrate third parties with the same functions. When using a component, as long as there is a class of the component on the class path, it will be automatically configured. For example, when spring boot web automatically configures the view component, it uses Velocity, Thymeleaf, or freemaker. This is the method used.
The example is two sets of armor A (light suit) and B (dark suit). If A is not present, configure 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 is a samurai and uses the suit to fight

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Van {
    private Fighter fighter;
    public void fight(){
        fighter.fight();
    }
}

VanConfigA/B instantiates the samurai

@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());
    }
}

Test class, by default, if suit AB is on the class path, Both sets will be loaded, and A will be set to PRIMARY. If FightA.class is deleted in the target class, only set B will be loaded.

@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();
    }
}

In addition, try to merge the two VanConfigA/B and put the annotation ConditionalOnClass on the method. If you delete a suit, an error will occur.

@ConditionalOnExpress

Perform conditional judgment based on expressions. This function can be used in most cases with @ConditionalOnProperty. The expression is more flexible because SpEL can be used. In the example, the value of test.enabled in properties will be judged. BeanConfig judges three types of Boolean, string and number respectively. I have tried many other methods but none of them work, such as using == directly. It seems that the configured attributes will be treated as strings.

@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());
    }
}

@ConditionalOnProperty

is suitable for conditional judgment on a single Property, while the @ConditionalOnExpress above is suitable for more complex situations, such as the associated comparison of multiple properties. This example also gives three basic types of conditional judgments, but it seems that they can all be treated as strings...

@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());

    }
}

@ConditionalOnJava

Can be judged by the java version.

@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>

@ConditionalOnResource

Conditional judgment is made based on whether the specified resource file exists, such as judging ehcache.properties to determine whether to automatically assemble the ehcache component.

@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>

@ConditionalOnSingleCandidate

I haven’t thought of the application scenario yet. The conditions for passing the condition are: 1. There is only one corresponding bean container. 2. There are multiple corresponding beans, but PRIMARY has been formulated. . In the example, when assembling BeanB, you need to check the assembly status of BeanA, so BeanBConfig should be ranked after BeanAConfig. You can modify BeanAConfig and remove the @Primary annotation, or remove the three @Bean annotations, and BeanB will not be instantiated.

@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>

@ConditionalOnNotWebApplication & @ConditionalOnWebApplication

Determine whether the current environment is a Web application.

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Those conditional judgments in Spring Boot## Java 19 Reading                                                             It takes 31 minutes to read                                                                                                                             

                                                                                                       

                                                                                                                                                                                                                                                                                                                                                                                  Those Conditionals in Spring Bootspring boot provides us with a wealth of Conditionals to make it very convenient for us to use them in the project Add beans to the container. This article mainly explains each annotation and illustrates its use with code. All ConditionalOnXXX annotations can be placed on class or method. If the method is on class, it will determine whether all @Bean annotated methods in the class are executed. @Conditional

The other Conditional annotations below are all syntactic sugar. You can customize ConditionalOnXXX through the following method.

The Conditional annotation is defined as follows and receives the class array that implements the Condition interface.

public @interface Conditional {
    Class extends Condition>[] value();
}

The Condition interface has only one matches method, which returns the result of matching.

public interface Condition {
    boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}

Configure conditions through the operating system to configure Bean. When Window is used, Bill's Person object is instantiated, and when Linux is used, Linus' Person object is instantiated.

//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>

Output results:

The current system is: Mac OS X

{linus=Person(name=Linus, age=48)}

@ConditionalOnBean & @ ConditionalOnMissingBean

These two annotations will judge the Bean object in the Bean container. The example used is during configuration. If it is found that there is no Computer instance, a backup computer will be instantiated.

@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>

Modify BeanConfig, if you comment out the first @Bean, the backup computer will be instantiated, otherwise the backup computer will not be instantiated

@ConditionalOnClass & @ConditionalOnMissingClass

This annotation will determine whether there is a specified class on the class path. It was confusing when I first saw it. If there is no specified class on the class path, the compilation will not pass... This is mainly used to integrate third parties with the same functions. When using a component, as long as there is a class of the component on the class path, it will be automatically configured. For example, when spring boot web automatically configures the view component, it uses Velocity, Thymeleaf, or freemaker. This is the method used.

The example is two sets of armor A (light suit) and B (dark suit). If A is not present, configure 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 is a samurai and uses the suit to fight

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Van {
    private Fighter fighter;
    public void fight(){
        fighter.fight();
    }
}

VanConfigA/B instantiates the samurai

@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());
    }
}

Test class, by default, if suit AB is on the class path, Both sets will be loaded, and A will be set to PRIMARY. If FightA.class is deleted in the target class, only set B will be loaded.

@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();
    }
}

In addition, try to merge the two VanConfigA/B and put the annotation ConditionalOnClass on the method. If you delete a suit, an error will occur.

@ConditionalOnExpress

Perform conditional judgment based on expressions. This function can be used in most cases with @ConditionalOnProperty. The expression is more flexible because SpEL can be used. In the example, the value of test.enabled in properties will be judged. BeanConfig judges three types of Boolean, string and number respectively. I have tried many other methods but none of them work, such as using == directly. It seems that the configured attributes will be treated as strings.

@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());
    }
}

@ConditionalOnProperty

is suitable for conditional judgment on a single Property, while the @ConditionalOnExpress above is suitable for more complex situations, such as the associated comparison of multiple properties. This example also gives three basic types of conditional judgments, but it seems that they can all be treated as strings...

@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());

    }
}

@ConditionalOnJava

Can be judged by the java version.

@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>

@ConditionalOnResource

Conditional judgment is made based on whether the specified resource file exists, such as judging ehcache.properties to determine whether to automatically assemble the ehcache component.

@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>

@ConditionalOnSingleCandidate

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>

@ConditionalOnNotWebApplication & @ConditionalOnWebApplication

判断当前环境是否是Web应用。

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