spring boot中的那些conditional
spring boot中为我们提供了丰富的conditional来让我们得以非常方便的在项目中向容器中添加bean。本文主要是对各个注解进行解释并辅以代码说明其用途。
所有conditionalonxxx的注解都可以放置在class或是method上，如果方式在class上，则会决定该class中所有的@bean注解方法是否执行。
@conditional
下面其他的conditional注解均是语法糖，可以通过下面的方法自定义conditionalonxxx
conditional注解定义如下，接收实现condition接口的class数组。
|
1 2 3 |
public @interface conditional { class <? extends condition>[] value(); } |
而condition接口只有一个matchs方法，返回是否匹配的结果。
|
1 2 3 |
public interface condition { boolean matches(conditioncontext context, annotatedtypemetadata metadata); } |
通过操作系统进行 条件判断 ，从而进行bean配置。当window时，实例化bill的person对象，当linux时，实例化linus的person对象。
|
1 2 3 4 5 6 7 |
//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 ; } } |
|
1 2 3 4 5 6 7 8 |
//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 |
|
1 2 3 4 5 6 7 |
@tostring @allargsconstructor @noargsconstructor public class person { private string name; private integer age; } |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 |
//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 ); } } |
|
1 2 3 4 5 6 7 8 9 10 11 |
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, person> map = applicationcontext.getbeansoftype(person. class ); system.out.println(map); } } |
输出的结果：
当前系统为：mac os x
{linus=person(name=linus, age=48)}
@conditionalonbean & @conditionalonmissingbean
这两个注解会对bean容器中的bean对象进行判断，使用的例子是配置的时候，如果发现如果没有computer实例，则实例化一个备用电脑。
|
1 2 3 4 5 6 |
@data @allargsconstructor @tostring public class computer { private string name; } |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
@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" ); } } |
|
1 2 3 4 5 6 7 8 |
public class testapp { annotationconfigapplicationcontext applicationcontext = new annotationconfigapplicationcontext(beanconfig. class ); @test public void test1(){ map<string,computer> map = applicationcontext.getbeansoftype(computer. class ); system.out.println(map); } } |
修改beanconfig,如果注释掉第一个@bean,会实例化备用电脑，否则就不会实例化备用电脑
@conditionalonclass & @conditionalonmissingclass
这个注解会判断类路径上是否有指定的类，一开始看到的时候比较困惑，类路径上如果没有指定的class,那编译也通过不了啊...这个主要用于集成相同功能的第三方组件时用，只要类路径上有该组件的类，就进行自动配置，比如spring boot web在自动配置视图组件时，是用velocity，还是thymeleaf,或是freemaker时，使用的就是这种方式。
例子是两套盔甲a(光明套装)和b(暗黑套装)，如果a不在则配置b。
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
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，使用套装进行战斗
|
1 2 3 4 5 6 7 8 9 |
@data @allargsconstructor @noargsconstructor public class van { private fighter fighter; public void fight(){ fighter.fight(); } } |
vanconfiga/b实例化武士
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
@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()); } } |
测试类,默认情况，如果套装ab都在类路径上，两套都会加载，a会设置为primary，如果在target class中将fighta.class删除，则只会加载套装b。
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
@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，尝试将两个vanconfiga/b合并，将注解conditionalonclass放到方法上，如果删除一个套装就会运行出错。
@conditionalonexpress
依据表达式进行条件判断，这个作用和@conditionalonproperty大部分情况可以通用，表达式更灵活一点,因为可以使用spel。例子中会判断properties中test.enabled的值进行判断。beanconfig分别对布尔，字符串和数字三种类型进行判断。数字尝试了很多其他的方式均不行，比如直接使用==，貌似配置的属性都会当成字符串来处理。
|
1 2 3 4 |
@data public class testbean { private string name; } |
|
1 2 3 4 5 6 7 8 9 10 |
@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" ); } } |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 |
@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
适合对单个property进行条件判断，而上面的@conditionalonexpress适合面对较为复杂的情况，比如多个property的关联比较。这个例子也给了三种基本类型的条件判断，不过貌似均当成字符串就可以...
|
1 2 3 4 5 6 |
@data @allargsconstructor @noargsconstructor public class testbean { private string name; } |
|
1 2 3 4 5 6 7 8 9 10 11 |
@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" ); } } |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 |
@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
可以通过java的版本进行判断。
|
1 2 3 |
@data public class testbean { } |
|
1 2 3 4 5 6 7 8 9 |
@configuration @conditionalonjava (javaversion.eight) public class beanconfig {
@bean public testbean testbean(){ return new testbean(); } } |
|
1 2 3 4 5 6 7 8 |
public class testapp { annotationconfigapplicationcontext context = new annotationconfigapplicationcontext(beanconfig. class ); @test public void test(){ map<string,testbean> map = context.getbeansoftype(testbean. class ); system.out.println(map); } } |
@conditionalonresource
通过指定的资源文件是否存在进行条件判断，比如判断ehcache.properties来决定是否自动装配ehcache组件。
|
1 2 3 |
@data public class testbean { } |
|
1 2 3 4 5 6 7 8 9 |
@configuration @conditionalonresource (resources = "classpath:application.yml" ) public class beanconfig {
@bean public testbean testbean(){ return new testbean(); } } |
|
1 2 3 4 5 6 7 8 9 |
public class testapp { annotationconfigapplicationcontext context = new annotationconfigapplicationcontext(beanconfig. class );
@test public void test(){ map<string,testbean> map = context.getbeansoftype(testbean. class ); system.out.println(map); } } |
@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。
|
1 2 3 4 5 6 |
@data @allargsconstructor @noargsconstructor public class beana { private string name; } |
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 |
@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" ); } } |
|
1 2 3 |
@data public class beanb { } |
|
1 2 3 4 5 6 7 8 9 10 |
@configuration @autoconfigureafter (beanaconfig. class ) @conditionalonsinglecandidate (beana. class ) public class beanbconfig {
@bean public beanb targetbean(){ return new beanb(); } } |
|
1 2 3 4 5 6 7 8 9 10 11 |
public class testapp { annotationconfigapplicationcontext context = new annotationconfigapplicationcontext(beanaconfig. class , beanbconfig. class );
@test public void test(){ map<string,beana> map = context.getbeansoftype(beana. class ); system.out.println(map); map<string,beanb> map2 = context.getbeansoftype(beanb. class ); system.out.println(map2); } } |
@conditionalonnotwebapplication & @conditionalonwebapplication
判断当前环境是否是web应用。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。
原文链接：https://segmentfault测试数据/a/1190000018831198
查看更多关于Spring Boot中的那些条件判断的实现方法的详细内容...