spring AnonymousBindMarkers 源码
spring AnonymousBindMarkers 代码
文件路径：/spring-r2dbc/src/main/java/org/springframework/r2dbc/core/binding/AnonymousBindMarkers.java
/*
* Copyright 2002-2020 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.r2dbc.core.binding;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
/**
* Anonymous, index-based bind marker using a static placeholder.
* Instances are bound by the ordinal position ordered by the appearance of
* the placeholder. This implementation creates indexed bind markers using
* an anonymous placeholder that correlates with an index.
*
* <p>Note: Anonymous bind markers are problematic because they have to appear
* in generated SQL in the same order they get generated. This might cause
* challenges in the future with complex generate statements. For example those
* containing subselects which limit the freedom of arranging bind markers.
*
* @author Mark Paluch
* @since 5.3
*/
class AnonymousBindMarkers implements BindMarkers {
private static final AtomicIntegerFieldUpdater<AnonymousBindMarkers> COUNTER_INCREMENTER =
AtomicIntegerFieldUpdater.newUpdater(AnonymousBindMarkers.class, "counter");
private final String placeholder;
// access via COUNTER_INCREMENTER
@SuppressWarnings("unused")
private volatile int counter = 0;
/**
* Create a new {@link AnonymousBindMarkers} instance given {@code placeholder}.
* @param placeholder parameter bind marker
*/
AnonymousBindMarkers(String placeholder) {
this.placeholder = placeholder;
}
@Override
public BindMarker next() {
int index = COUNTER_INCREMENTER.getAndIncrement(this);
return new IndexedBindMarkers.IndexedBindMarker(this.placeholder, index);
}
}
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