jfinal enjoy 3.5

src/main/java/com/jfinal/template/expr/ast/FieldKeyBuilder.java

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+/**
+ * Copyright (c) 2011-2019, James Zhan 詹波 (jfinal@126.com).
+ *
+ * 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
+ *
+ *      http://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 com.jfinal.template.expr.ast;
+
+/**
+ * FieldKeyBuilder
+ * 
+ * 用于生成缓存 FieldGetter 的 key
+ */
+public abstract class FieldKeyBuilder {
+	
+	public abstract Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash);
+	
+	// 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
+	static FieldKeyBuilder instance = new StrictFieldKeyBuilder();
+	
+	public static FieldKeyBuilder getInstance() {
+		return instance;
+	}
+	
+	/**
+	 * 设置为官方提供的 FastFieldKeyBuilder 实现，性能更高
+	 */
+	public static void setToFastFieldKeyBuilder() {
+		instance = new FastFieldKeyBuilder();
+	}
+	
+	/**
+	 * 设置为自定义 FieldKeyBuilder
+	 */
+	public static void setFieldKeyBuilder(FieldKeyBuilder fieldKeyBuilder) {
+		if (fieldKeyBuilder == null) {
+			throw new IllegalArgumentException("fieldKeyBuilder can not be null");
+		}
+		instance = fieldKeyBuilder;
+	}
+	
+	// ------------------------------------------------------------------------
+	
+	/**
+	 * FastFieldKeyBuilder
+	 */
+	public static class FastFieldKeyBuilder extends FieldKeyBuilder {
+		public Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash) {
+			return targetClass.getName().hashCode() ^ fieldFnv1a64Hash;
+		}
+	}
+	
+	// ------------------------------------------------------------------------
+	
+	/**
+	 * StrictFieldKeyBuilder
+	 */
+	public static class StrictFieldKeyBuilder extends FieldKeyBuilder {
+		public Object getFieldKey(Class<?> targetClass, long fieldFnv1a64Hash) {
+			return new FieldKey(targetClass.getName().hashCode(), fieldFnv1a64Hash);
+		}
+	}
+	
+	// ------------------------------------------------------------------------
+	
+	/**
+	 * FieldKey
+	 * 
+	 * FieldKey 用于封装 targetClass、fieldName 这两部分的 hash 值，
+	 * 确保不会出现 key 值碰撞
+	 * 
+	 * 这两部分 hash 值在不同 class 与 field 的组合下出现碰撞的
+	 * 概率完全可以忽略不计
+	 * 
+	 * 备忘：
+	 * 可以考虑用 ThreadLocal 重用 FieldKey 对象，但要注意放入 Map fieldGetterCache
+	 * 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，
+	 * 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
+	 * 避免创建对象
+	 */
+	public static class FieldKey {
+		
+		final long classHash;
+		final long fieldHash;
+		
+		public FieldKey(long classHash, long fieldHash) {
+			this.classHash = classHash;
+			this.fieldHash = fieldHash;
+		}
+		
+		public int hashCode() {
+			return (int)(classHash ^ fieldHash);
+		}
+		
+		/**
+		 * 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
+		 * 
+		 * 不必判断 if (fieldKey instanceof FieldKey)，因为所有 key 类型必须要相同
+		 * 不必判断 if (this == fieldKey)，因为每次用于取值的 FieldKey 都是新建的
+		 */
+		public boolean equals(Object fieldKey) {
+			FieldKey fk = (FieldKey)fieldKey;
+			return classHash == fk.classHash && fieldHash == fk.fieldHash;
+		}
+		
+		public String toString() {
+			return "classHash = " + classHash + "\nfieldHash = " + fieldHash;
+		}
+	}
+}
+
+
+
+
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