config/src/main/java/org/springframework/security/config/annotation/web/configurers/SessionManagementConfigurer.java
InvalidSessionStrategy getInvalidSessionStrategy() {
		if (this.invalidSessionStrategy != null) {
			return this.invalidSessionStrategy;
		}
		if (this.invalidSessionUrl != null) {
			this.invalidSessionStrategy = new SimpleRedirectInvalidSessionStrategy(
					this.invalidSessionUrl);
		}
		if (this.invalidSessionUrl == null) {
			return null;
		}
		if (this.invalidSessionStrategy == null) {
			this.invalidSessionStrategy = new SimpleRedirectInvalidSessionStrategy(
					this.invalidSessionUrl);
		}
		return this.invalidSessionStrategy;
	}
InvalidSessionStrategy getInvalidSessionStrategy() {
		if (this.invalidSessionStrategy != null) {
			return this.invalidSessionStrategy;
		}
		if (this.invalidSessionUrl != null) {
			this.invalidSessionStrategy = new SimpleRedirectInvalidSessionStrategy(
					this.invalidSessionUrl);
		}
		if (this.invalidSessionUrl == null) {
			return null;
		}
		if (this.invalidSessionStrategy == null) {
			this.invalidSessionStrategy = new SimpleRedirectInvalidSessionStrategy(
					this.invalidSessionUrl);
		}
		return this.invalidSessionStrategy;
	}
Gets the {@link InvalidSessionStrategy} to use. If null and
{@link #invalidSessionUrl} is not null defaults to
{@link SimpleRedirectInvalidSessionStrategy}.

@return the {@link InvalidSessionStrategy} to use