org.springframework.core.AttributeAccessor Maven / Gradle / Ivy
/*
* Copyright 2002-2021 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.core;
import java.util.function.Function;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
/**
* Interface defining a generic contract for attaching and accessing metadata
* to/from arbitrary objects.
*
* @author Rob Harrop
* @author Sam Brannen
* @since 2.0
*/
public interface AttributeAccessor {
/**
* Set the attribute defined by {@code name} to the supplied {@code value}.
* If {@code value} is {@code null}, the attribute is {@link #removeAttribute removed}.
*
In general, users should take care to prevent overlaps with other
* metadata attributes by using fully-qualified names, perhaps using
* class or package names as prefix.
* @param name the unique attribute key
* @param value the attribute value to be attached
*/
void setAttribute(String name, @Nullable Object value);
/**
* Get the value of the attribute identified by {@code name}.
*
Return {@code null} if the attribute doesn't exist.
* @param name the unique attribute key
* @return the current value of the attribute, if any
*/
@Nullable
Object getAttribute(String name);
/**
* Compute a new value for the attribute identified by {@code name} if
* necessary and {@linkplain #setAttribute set} the new value in this
* {@code AttributeAccessor}.
*
If a value for the attribute identified by {@code name} already exists
* in this {@code AttributeAccessor}, the existing value will be returned
* without applying the supplied compute function.
*
The default implementation of this method is not thread safe but can
* be overridden by concrete implementations of this interface.
* @param the type of the attribute value
* @param name the unique attribute key
* @param computeFunction a function that computes a new value for the attribute
* name; the function must not return a {@code null} value
* @return the existing value or newly computed value for the named attribute
* @since 5.3.3
* @see #getAttribute(String)
* @see #setAttribute(String, Object)
*/
@SuppressWarnings("unchecked")
default T computeAttribute(String name, Function computeFunction) {
Assert.notNull(name, "Name must not be null");
Assert.notNull(computeFunction, "Compute function must not be null");
Object value = getAttribute(name);
if (value == null) {
value = computeFunction.apply(name);
Assert.state(value != null,
() -> String.format("Compute function must not return null for attribute named '%s'", name));
setAttribute(name, value);
}
return (T) value;
}
/**
* Remove the attribute identified by {@code name} and return its value.
* Return {@code null} if no attribute under {@code name} is found.
* @param name the unique attribute key
* @return the last value of the attribute, if any
*/
@Nullable
Object removeAttribute(String name);
/**
* Return {@code true} if the attribute identified by {@code name} exists.
*
Otherwise return {@code false}.
* @param name the unique attribute key
*/
boolean hasAttribute(String name);
/**
* Return the names of all attributes.
*/
String[] attributeNames();
}