Introduce IndexResolver

This commit introduces IndexResolver as a strategy interface for resolving index values in FindByIndexNameSessionRepository implementations.

Resolves: #557

spring-session-core/src/main/java/org/springframework/session/DelegatingIndexResolver.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2014-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.session;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * An {@link IndexResolver} that resolves indexes using multiple @{link IndexResolver}
+ * delegates.
+ *
+ * @param <S> the type of Session being handled
+ * @author Vedran Pavic
+ * @since 2.2.0
+ */
+public class DelegatingIndexResolver<S extends Session> implements IndexResolver<S> {
+
+	private final List<IndexResolver<S>> delegates;
+
+	public DelegatingIndexResolver(List<IndexResolver<S>> delegates) {
+		this.delegates = Collections.unmodifiableList(delegates);
+	}
+
+	@SafeVarargs
+	public DelegatingIndexResolver(IndexResolver<S>... delegates) {
+		this(Arrays.asList(delegates));
+	}
+
+	public Map<String, String> resolveIndexesFor(S session) {
+		Map<String, String> indexes = new HashMap<>();
+		for (IndexResolver<S> delegate : this.delegates) {
+			indexes.putAll(delegate.resolveIndexesFor(session));
+		}
+		return indexes;
+	}
+
+}

spring-session-core/src/main/java/org/springframework/session/IndexResolver.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2014-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.session;
+
+import java.util.Map;
+
+/**
+ * Strategy interface for resolving the {@link Session}'s indexes.
+ *
+ * @param <S> the type of Session being handled
+ * @author Rob Winch
+ * @author Vedran Pavic
+ * @since 2.2.0
+ * @see FindByIndexNameSessionRepository
+ */
+public interface IndexResolver<S extends Session> {
+
+	/**
+	 * Resolve indexes for the session.
+	 * @param session the session
+	 * @return a map of resolved indexes, never {@code null}
+	 */
+	Map<String, String> resolveIndexesFor(S session);
+
+}

spring-session-core/src/main/java/org/springframework/session/PrincipalNameIndexResolver.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2014-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.session;
+
+import org.springframework.expression.Expression;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+
+/**
+ * {@link IndexResolver} to resolve the principal name from session attribute named
+ * {@link FindByIndexNameSessionRepository#PRINCIPAL_NAME_INDEX_NAME} or Spring Security
+ * context stored in the session under {@code SPRING_SECURITY_CONTEXT} attribute.
+ *
+ * @param <S> the type of Session being handled
+ * @author Vedran Pavic
+ * @since 2.2.0
+ */
+public class PrincipalNameIndexResolver<S extends Session> extends SingleIndexResolver<S> {
+
+	private static final String SPRING_SECURITY_CONTEXT = "SPRING_SECURITY_CONTEXT";
+
+	private static final SpelExpressionParser parser = new SpelExpressionParser();
+
+	public PrincipalNameIndexResolver() {
+		super(FindByIndexNameSessionRepository.PRINCIPAL_NAME_INDEX_NAME);
+	}
+
+	public String resolveIndexValueFor(S session) {
+		String principalName = session.getAttribute(getIndexName());
+		if (principalName != null) {
+			return principalName;
+		}
+		Object authentication = session.getAttribute(SPRING_SECURITY_CONTEXT);
+		if (authentication != null) {
+			Expression expression = parser.parseExpression("authentication?.name");
+			return expression.getValue(authentication, String.class);
+		}
+		return null;
+	}
+
+}

spring-session-core/src/main/java/org/springframework/session/SingleIndexResolver.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2014-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.session;
+
+import java.util.Collections;
+import java.util.Map;
+
+import org.springframework.util.Assert;
+
+/**
+ * Base class for {@link IndexResolver}s that resolve a single index.
+ *
+ * @param <S> the type of Session being handled
+ * @author Rob Winch
+ * @author Vedran Pavic
+ * @since 2.2.0
+ */
+public abstract class SingleIndexResolver<S extends Session> implements IndexResolver<S> {
+
+	private final String indexName;
+
+	protected SingleIndexResolver(String indexName) {
+		Assert.notNull(indexName, "Index name must not be null");
+		this.indexName = indexName;
+	}
+
+	protected String getIndexName() {
+		return this.indexName;
+	}
+
+	public abstract String resolveIndexValueFor(S session);
+
+	public final Map<String, String> resolveIndexesFor(S session) {
+		String indexValue = resolveIndexValueFor(session);
+		return (indexValue != null) ? Collections.singletonMap(this.indexName, indexValue) : Collections.emptyMap();
+	}
+
+}