一、占位符解析器源码
1、占位符解析器实现的目标
通过解析字符串中指定前后缀中的字符，并完成相应的功能。
在mybtias中的应用，主要是为了解析Mapper的xml中的sql语句#{}中的内容，识别当前sql语句的一些特性。
2、占位符解析器的通用算法类
(1)org.apache.ibatis.parsing.GenericTokenParser
public class GenericTokenParser { private final String openToken; private final String closeToken; private final TokenHandler handler; public GenericTokenParser(String openToken, String closeToken, TokenHandler handler) { this.openToken = openToken; this.closeToken = closeToken; this.handler = handler; } public String parse(String text) { final StringBuilder builder = new StringBuilder(); final StringBuilder expression = new StringBuilder(); if (text != null && text.length() > 0) { char[] src = text.toCharArray(); int offset = 0; // search open token int start = text.indexOf(openToken, offset); while (start > -1) { if (start > 0 && src[start - 1] == '\\') { // this open token is escaped. remove the backslash and continue. builder.append(src, offset, start - offset - 1).append(openToken); offset = start + openToken.length(); } else { // found open token. let's search close token. 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] == '\\') { // this close token is escaped. remove the backslash and continue. expression.append(src, offset, end - offset - 1).append(closeToken); offset = end + closeToken.length(); end = text.indexOf(closeToken, offset); } else { expression.append(src, offset, end - offset); offset = end + closeToken.length(); break; } } if (end == -1) { // close token was not found. builder.append(src, start, src.length - start); offset = src.length; } else { 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); } } return builder.toString(); } }
解析占位符中的字符串的接口类
(2)org.apache.ibatis.parsing.TokenHandler
public interface TokenHandler { String handleToken(String content); }
(3)解析sql语句中的参数绑定的tokenHandler的实现类
org.apache.ibatis.builder.ParameterMappingTokenHandler
/** * Copyright 2009-2015 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 * * 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 org.apache.ibatis.builder; import java.util.ArrayList; import java.util.List; import java.util.Map; import org.apache.ibatis.mapping.ParameterMapping; import org.apache.ibatis.mapping.SqlSource; import org.apache.ibatis.parsing.GenericTokenParser; import org.apache.ibatis.parsing.TokenHandler; import org.apache.ibatis.reflection.MetaClass; import org.apache.ibatis.reflection.MetaObject; import org.apache.ibatis.session.Configuration; import org.apache.ibatis.type.JdbcType; /** * @author Clinton Begin */ public class SqlSourceBuilder extends BaseBuilder { private static final String parameterProperties = "javaType,jdbcType,mode,numericScale,resultMap,typeHandler,jdbcTypeName"; public SqlSourceBuilder(Configuration configuration) { super(configuration); } public SqlSource parse(String originalSql, Class<?> parameterType, Map<String, Object> additionalParameters) { ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration, parameterType, additionalParameters); GenericTokenParser parser = new GenericTokenParser("#{", "}", handler); String sql = parser.parse(originalSql); return new StaticSqlSource(configuration, sql, handler.getParameterMappings()); } private static class ParameterMappingTokenHandler extends BaseBuilder implements TokenHandler { private List<ParameterMapping> parameterMappings = new ArrayList<ParameterMapping>(); private Class<?> parameterType; private MetaObject metaParameters; public ParameterMappingTokenHandler(Configuration configuration, Class<?> parameterType, Map<String, Object> additionalParameters) { super(configuration); this.parameterType = parameterType; this.metaParameters = configuration.newMetaObject(additionalParameters); } public List<ParameterMapping> getParameterMappings() { return parameterMappings; } @Override public String handleToken(String content) { parameterMappings.add(buildParameterMapping(content)); return "?"; } private ParameterMapping buildParameterMapping(String content) { Map<String, String> propertiesMap = parseParameterMapping(content); String property = propertiesMap.get("property"); Class<?> propertyType; if (metaParameters.hasGetter(property)) { // issue #448 get type from additional params propertyType = metaParameters.getGetterType(property); } else if (typeHandlerRegistry.hasTypeHandler(parameterType)) { propertyType = parameterType; } else if (JdbcType.CURSOR.name().equals(propertiesMap.get("jdbcType"))) { propertyType = java.sql.ResultSet.class; } else if (property != null) { MetaClass metaClass = MetaClass.forClass(parameterType, configuration.getReflectorFactory()); if (metaClass.hasGetter(property)) { propertyType = metaClass.getGetterType(property); } else { propertyType = Object.class; } } else { propertyType = Object.class; } ParameterMapping.Builder builder = new ParameterMapping.Builder(configuration, property, propertyType); Class<?> javaType = propertyType; String typeHandlerAlias = null; for (Map.Entry<String, String> entry : propertiesMap.entrySet()) { String name = entry.getKey(); String value = entry.getValue(); if ("javaType".equals(name)) { javaType = resolveClass(value); builder.javaType(javaType); } else if ("jdbcType".equals(name)) { builder.jdbcType(resolveJdbcType(value)); } else if ("mode".equals(name)) { builder.mode(resolveParameterMode(value)); } else if ("numericScale".equals(name)) { builder.numericScale(Integer.valueOf(value)); } else if ("resultMap".equals(name)) { builder.resultMapId(value); } else if ("typeHandler".equals(name)) { typeHandlerAlias = value; } else if ("jdbcTypeName".equals(name)) { builder.jdbcTypeName(value); } else if ("property".equals(name)) { // Do Nothing } else if ("expression".equals(name)) { throw new BuilderException("Expression based parameters are not supported yet"); } else { throw new BuilderException("An invalid property '" + name + "' was found in mapping #{" + content + "}. Valid properties are " + parameterProperties); } } if (typeHandlerAlias != null) { builder.typeHandler(resolveTypeHandler(javaType, typeHandlerAlias)); } return builder.build(); } private Map<String, String> parseParameterMapping(String content) { try { return new ParameterExpression(content); } catch (BuilderException ex) { throw ex; } catch (Exception ex) { throw new BuilderException("Parsing error was found in mapping #{" + content + "}. Check syntax #{property|(expression), var1=value1, var2=value2, ...} ", ex); } } } }
#{department, mode=OUT, jdbcType=CURSOR, javaType=ResultSet, resultMap=departmentResultMap}
其功能时将xml中配置的sql语句里"#{", "}"中间的字符串，知道该sql语句中的参数信息
1、参数在mapp接口入参的bean的属性名
2、该属性是什么数据类型
3、在数据库中映射成什么jdbc类型
4、参数转换的TypeHandler的类信息
二、策略模式的应用
https://www.cnblogs.com/shangxiaofei/p/5146107.html
将不同的算法独立封装。
新增或减少算法，对使用算法者无影响。
不同的场景使用不同的算法。