SpringBoot基础篇Bean之@ConditionalOnBean与@ConditionalOnClass

@Component
@ConditionalOnBean(name="redisTemplate")
public class RedisOperBean {
  private final RedisTemplate redisTemplate;
  public RedisOperBean(RedisTemplate redisTemplate) {
      // ...
  }
}

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
  // bean类型
	Class<?>[] value() default {};

	// bean类型
	String[] type() default {};

	// 要求bean上拥有指定的注解
	Class<? extends Annotation>[] annotation() default {};

	// bean names
	String[] name() default {};

	SearchStrategy search() default SearchStrategy.ALL;
}

public class DependedBean {
}

public class LoadIfBeanExist {

    private String name;

    public LoadIfBeanExist(String name) {
        this.name = name;
    }

    public String getName() {
        return "load if bean exists: " + name;
    }
}

@Bean
public DependedBean dependedBean() {
    return new DependedBean();
}

/**
 * 只有当DependedBean 存在时，才会创建bean: `LoadIfBeanExist`
 *
 * @return
 */
@Bean
@ConditionalOnBean(name = "dependedBean")
public LoadIfBeanExist loadIfBeanExist() {
    return new LoadIfBeanExist("dependedBean");
}

public @interface ConditionalOnMissingBean {
	Class<?>[] value() default {};

	String[] type() default {};

	/**
	 * The class type of beans that should be ignored when identifying matching beans.
	 */
	Class<?>[] ignored() default {};

	/**
	 * The class type names of beans that should be ignored when identifying matching
	 * beans.
	 */
	String[] ignoredType() default {};

	Class<? extends Annotation>[] annotation() default {};

	String[] name() default {};

	SearchStrategy search() default SearchStrategy.ALL;
}

public class LoadIfBeanNotExists {
    public String name;

    public LoadIfBeanNotExists(String name) {
        this.name = name;
    }

    public String getName() {
        return "load if bean not exists: " + name;
    }
}

/**
 * 只有当没有notExistsBean时，才会创建bean: `LoadIfBeanNotExists`
 *
 * @return
 */
@Bean
@ConditionalOnMissingBean(name = "notExistsBean")
public LoadIfBeanNotExists loadIfBeanNotExists() {
    return new LoadIfBeanNotExists("notExistsBean");
}

public @interface ConditionalOnClass {
	Class<?>[] value() default {};

	/**
	 * The classes names that must be present.
	 * @return the class names that must be present.
	 */
	String[] name() default {};

}

public class DependedClz {
}

public class LoadIfClzExists {
    private String name;

    public LoadIfClzExists(String name) {
        this.name = name;
    }

    public String getName() {
        return "load if exists clz: " + name;
    }
}

/**
 * 当引用了 {@link DependedClz} 类之后，才会创建bean： `LoadIfClzExists`
 *
 * @return
 */
@Bean
@ConditionalOnClass(DependedClz.class)
public LoadIfClzExists loadIfClzExists() {
    return new LoadIfClzExists("dependedClz");
}

public @interface ConditionalOnMissingClass {
	String[] value() default {};
}

public class LoadIfClzNotExists {
    private String name;

    public LoadIfClzNotExists(String name) {
        this.name = name;
    }

    public String getName() {
        return "load if not exists clz: " + name;
    }
}

/**
 * 当系统中没有 com.git.hui.boot.conditionbean.example.depends.clz.DependedClz类时，才会创建这个bean
 *
 * @return
 */
@Bean
@ConditionalOnMissingClass("com.git.hui.boot.conditionbean.example.depends.clz.DependedClz")
public LoadIfClzNotExists loadIfClzNotExists() {
    return new LoadIfClzNotExists("com.git.hui.boot.conditionbean.example.depends.clz.DependedClz");
}

@RestController
@RequestMapping("depends")
public class DependRest {

    @Autowired
    private LoadIfBeanExist loadIfBeanExist;
    @Autowired
    private LoadIfBeanNotExists loadIfBeanNotExists;
    @Autowired
    private LoadIfClzExists loadIfClzExists;
    @Autowired(required = false)
    private LoadIfClzNotExists loadIfClzNotExists;

    @GetMapping(path = "show")
    public String show() {
        Map<String, String> result = new HashMap<>(4);
        // 存在
        result.put("loadIfBeanExist", loadIfBeanExist == null ? "null ==> false!" : loadIfBeanExist.getName());
        // 存在
        result.put("loadIfBeanNotExists",
                loadIfBeanNotExists == null ? "null ==> false!" : loadIfBeanNotExists.getName());
        // 存在
        result.put("loadIfClzExists", loadIfClzExists == null ? "null ==> false!" : loadIfClzExists.getName());
        // 不存在
        result.put("loadIfClzNotExists", loadIfClzNotExists == null ? "null ==> true!" : loadIfClzNotExists.getName());

        return JSONObject.toJSONString(result);
    }
}