GenericTokenParser 源码

Author: huifer

docs/Mybatis/HuiFer-Mybats-GenericTokenParser.md

@@ -0,0 +1,175 @@
+# GenericTokenParser
+- Author: [HuiFer](https://github.com/huifer)
+
+```java
+/**
+ * Copyright 2009-2019 the original author or authors.
+ * <p>
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.apache.ibatis.parsing;
+
+/**
+ * @author Clinton Begin
+ */
+public class GenericTokenParser {
+
+    /**
+     * 开始标记
+     */
+    private final String openToken;
+    /**
+     * 结束标记
+     */
+    private final String closeToken;
+    /**
+     * 标记处理器
+     */
+    private final TokenHandler handler;
+
+    public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) {
+        this.openToken = openToken;
+        this.closeToken = closeToken;
+        this.handler = handler;
+    }
+
+    /**
+     * 核心处理方法 , 看测试类{@link org.apache.ibatis.parsing.GenericTokenParserTest}
+     * @param text
+     * @return
+     */
+    public String parse(String text) {
+        // 判断是否空
+        if (text == null || text.isEmpty()) {
+            return "";
+        }
+        // search open token
+        // 判断 openToken 所在的位置-1不存在
+        int start = text.indexOf(openToken);
+        if (start == -1) {
+            return text;
+        }
+        char[] src = text.toCharArray();
+        int offset = 0;
+        final StringBuilder builder = new StringBuilder();
+        StringBuilder expression = null;
+
+        // 循环处理         assertEquals("James T Kirk reporting.", parser.parse("${first_name} ${initial} ${last_name} reporting."));
+        // 将${} 转换成正常文本
+        while (start > -1) {
+            if (start > 0 && src[start - 1] == '\\') {
+                // `\` 忽略这个参数
+                // this open token is escaped. remove the backslash and continue.
+                builder.append(src, offset, start - offset - 1).append(openToken);
+                // offset 重新计算进行下一步循环
+                offset = start + openToken.length();
+            } else {
+                // found open token. let's search close token.
+                if (expression == null) {
+                    expression = new StringBuilder();
+                } else {
+                    expression.setLength(0);
+                }
+                builder.append(src, offset, start - offset);
+                offset = start + openToken.length();
+                int end = text.indexOf(closeToken, offset);
+                while (end > -1) {
+                    if (end > offset && src[end - 1] == '\\') {
+                        // 遇到`\`该参数不需要处理
+                        // this close token is escaped. remove the backslash and continue.
+                        expression.append(src, offset, end - offset - 1).append(closeToken);
+                        // 计算offset重新推算替换的字符串
+                        offset = end + closeToken.length();
+                        end = text.indexOf(closeToken, offset);
+                    } else {
+                        expression.append(src, offset, end - offset);
+                        break;
+                    }
+                }
+                if (end == -1) {
+                    // end == -1 closeToken 不存在,获取后面的所有字符串, openToken - closeToken 之间的内容
+                    // close token was not found.
+                    builder.append(src, start, src.length - start);
+                    offset = src.length;
+                } else {
+                    // closeToken存在 继续执行
+                    builder.append(handler.handleToken(expression.toString()));
+                    offset = end + closeToken.length();
+                }
+            }
+            start = text.indexOf(openToken, offset);
+        }
+        if (offset < src.length) {
+            builder.append(src, offset, src.length - offset);
+        }
+        // 返回的是一个替换后的sql脚本
+        return builder.toString();
+    }
+}
+
+```
+
+
+- 一个具体的例子`org.apache.ibatis.builder.SqlSourceBuilder.ParameterMappingTokenHandler`
+    - 具体类`org.apache.ibatis.builder.SqlSourceBuilder`
+```java
+        /**
+         * ? 的来源
+         *
+         * @param content
+         * @return
+         */
+        @Override
+        public String handleToken(String content) {
+            parameterMappings.add(buildParameterMapping(content));
+            return "?";
+        }
+
+```
+```java
+    /**
+     * sql 参数类型 ， 返回值
+     *
+     * <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
+     * <!--@mbg.generated-->
+     * select
+     * <include refid="Base_Column_List" />
+     * from hs_sell
+     * where ID = #{id,jdbcType=INTEGER}
+     * </select>
+     * => 替换成问号
+     * select
+     * <p>
+     * <p>
+     * ID, USER_ID, GOOD_ID, PRICE, `SIZE`, COMPANY_ID, GROUP_ID, VERSION, DELETED, CREATE_USER,
+     * CREATE_TIME, UPDATE_USER, UPDATE_TIME, WORK_ORDER_ID
+     * <p>
+     * from hs_sell
+     * where ID = ?
+     *
+     * @param originalSql          sql文本
+     * @param parameterType        默认 object
+     * @param additionalParameters
+     * @return
+     */
+    public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) {
+        ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters);
+//        org.apache.ibatis.builder.SqlSourceBuilder.ParameterMappingTokenHandler.handleToken
+        GenericTokenParser parser = new GenericTokenParser("#{", "}", handler);
+        String sql = parser.parse(originalSql);
+        return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
+    }
+
+```
+
+![image-20191219100446796](/images/mybatis/image-20191219100446796.png)