133 lines
3.9 KiB
Java
133 lines
3.9 KiB
Java
/**
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* Copyright (c) 2011-2019, James Zhan 詹波 (jfinal@126.com).
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.jfinal.template.expr.ast;
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/**
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* FieldKeyBuilder
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*
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* 用于生成缓存 FieldGetter 的 key
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*/
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public abstract class FieldKeyBuilder {
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public abstract Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash);
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// 假定是超大规模项目，并且假定其 Map/Model/Record + field 组合数量超级庞大，默认使用 StrictFieldKeyBuilder
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static FieldKeyBuilder instance = new StrictFieldKeyBuilder();
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public static FieldKeyBuilder getInstance() {
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return instance;
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}
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/**
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* 开启 FastFieldKeyBuilder，性能更高
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*/
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public static void setFastFieldKeyBuilder(boolean enable) {
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if (enable) {
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instance = new FastFieldKeyBuilder();
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} else {
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instance = new StrictFieldKeyBuilder();
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}
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}
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/**
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* 设置为自定义 FieldKeyBuilder
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*/
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public static void setFieldKeyBuilder(FieldKeyBuilder fieldKeyBuilder) {
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if (fieldKeyBuilder == null) {
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throw new IllegalArgumentException("fieldKeyBuilder can not be null");
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}
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instance = fieldKeyBuilder;
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}
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// ------------------------------------------------------------------------
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/**
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* FastFieldKeyBuilder
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*/
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public static class FastFieldKeyBuilder extends FieldKeyBuilder {
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public Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash) {
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return targetClass.getName().hashCode() ^ fieldFnv1a64Hash;
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}
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}
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// ------------------------------------------------------------------------
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/**
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* StrictFieldKeyBuilder
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*/
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public static class StrictFieldKeyBuilder extends FieldKeyBuilder {
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public Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash) {
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return new FieldKey(targetClass.getName().hashCode(), fieldFnv1a64Hash);
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}
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}
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// ------------------------------------------------------------------------
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/**
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* FieldKey
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*
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* FieldKey 用于封装 targetClass、fieldName 这两部分的 hash 值，
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* 确保不会出现 key 值碰撞
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*
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* 这两部分 hash 值在不同 class 与 field 的组合下出现碰撞的
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* 概率完全可以忽略不计
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*
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* 备忘：
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* 可以考虑用 ThreadLocal 重用 FieldKey 对象，但要注意放入 Map fieldGetterCache
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* 中的 FieldKey 对象需要 clone 出来，确保线程安全。由于 FieldKey 占用空间不大，
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* 所以 ThreadLocal 方案大概率并无优势，从 ThreadLocal 中获取数据时，除了耗时也无法
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* 避免创建对象
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*/
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public static class FieldKey {
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final long classHash;
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final long fieldHash;
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public FieldKey(long classHash, long fieldHash) {
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this.classHash = classHash;
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this.fieldHash = fieldHash;
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}
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public int hashCode() {
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return (int)(classHash ^ fieldHash);
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}
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/**
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* FieldKey 的核心价值在于此 equals 方法通过比较两部分 hash 值，避免超大规模场景下可能的 key 值碰撞
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*
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* 不必判断 if (fieldKey instanceof FieldKey)，因为所有 key 类型必须要相同
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* 不必判断 if (this == fieldKey)，因为每次用于取值的 FieldKey 都是新建的
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*/
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public boolean equals(Object fieldKey) {
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FieldKey fk = (FieldKey)fieldKey;
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return classHash == fk.classHash && fieldHash == fk.fieldHash;
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}
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public String toString() {
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return "classHash = " + classHash + "\nfieldHash = " + fieldHash;
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}
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}
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}
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