MyBatis 通过拦截修改SQL
假如我们想实现多租户，或者在某些SQL后面自动拼接查询条件。在开发过程中大部分场景可能都是一个查询写一个SQL去处理，我们如果想修改最终SQL可以通过修改各个mapper.xml中的SQL来处理。但实际过程中我们可能穿插着ORM和SQL的混合使用，隐藏在代码中不容易被发现，还有假如项目中有很多很多的SQL我们不可能一一的去修改解决。这个时候我们就需要通过mybatis拦截SQL并且最终修改SQL。
maven依赖
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatis-springartifactId>
<version>2.0.4version>
dependency>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-coreartifactId>
<version>5.2.4.RELEASEversion>
<scope>compilescope>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>8.0.26version>
dependency>
<dependency>
<groupId>com.github.jsqlparsergroupId>
<artifactId>jsqlparserartifactId>
<version>4.2version>
dependency>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatis-springartifactId>
<version>2.0.4version>
dependency>
<dependency>
<groupId>com.baomidougroupId>
<artifactId>mybatis-plusartifactId>
<version>2.3.3version>
dependency>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.4version>
dependency>
<dependency>
<groupId>com.alibabagroupId>
<artifactId>druid-spring-boot-starterartifactId>
<version>1.2.6version>
dependency>
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
dependency>
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
dependency>
配置部分
这部分是传统mybatis的xml配置，如果是Springboot项目或者使用JavaConfig配置的请查看官方文档配置方式。无非就是Springboot封装了mybatis-xxx-stater包将部分配置都转为了参数控制以及部分autoconfig，大同小异这里不做过多讨论。
DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="db.properties">properties>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING" />
<setting name="cacheEnabled" value="false"/>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>
<setting name="localCacheScope" value="SESSION"/>
settings>
<plugins>
<plugin interceptor="com.allens.mybatis.interceptor.SQLInterceptor"/>
<plugin interceptor="com.allens.mybatis.interceptor.SQLParamInterceptor"/>
plugins>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value=""/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="mappers/UserMapper.xml"/>
mappers>
configuration>
整个拦截调用链路流程图：
① mybatis在这一层包装了StatementHandler返回代理对象，下一步调用prepare的时候会先调用增强拦截器。
Configuration.newStatementHandler
public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
// 对statementhandler进行代理
statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
return statementHandler;
}
InterceptorChain.pluginAll
public Object pluginAll(Object target) {
for (Interceptor interceptor : interceptors) {
target = interceptor.plugin(target);
}
return target;
}
Interceptor.plugin
default Object plugin(Object target) {
return Plugin.wrap(target, this);
}
包装成代理对象
Plugin.wrap
public static Object wrap(Object target, Interceptor interceptor) {
Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
Class<?> type = target.getClass();
// 获取target对象的所有接口类型
Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
if (interfaces.length > 0) {
// 学习过JDK动态代理的同学对这段代码肯定很熟，这里是生成一个代理对象
return Proxy.newProxyInstance(
type.getClassLoader(), // 类加载器
interfaces, // JDK动态代理必须要有接口
new Plugin(target, interceptor, signatureMap));
}
return target;
}
如果大家觉得这篇文章写的还可以请关注我，我后续会出
mybatis的源码解析。
调用代码
这部分代码负责调用mybatis，如果使用springboot这部分就是你的rest接口。
import com.allens.mybatis.model.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class TestMybatis {
public static void main(String[] args) throws IOException {
// 读取配置文件
InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
// 通过SqlSessionFactoryBuilder创建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
// 获取到SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
// 调用Mapper中的指定方法 com.wyh.mapper.UserMapper.queryAll是statementId
Map<String, Object> map = new HashMap<>();
map.put("pageSize", 1);
map.put("desc", "desc");
map.put("name", "Allens");
List<User> userList = sqlSession.selectList("com.allens.mybatis.mappers.UserMapper.selectUsers", map);
System.out.println("++++++++++++++++++++++");
userList.forEach(System.out::println);
}
}
拦截器的代码实现
这使用了Druid的SQLParser进行解析SQL，如果不想使用druid可以使用
sqlparser包进行sql解析。不管用什么样的工具把SQL修改掉就行了，形式不限。
如果想使用sqlparser进行解析sql可以看我的下一篇文章
JSqlparser 使用攻略（高效的SQL解析工具）
/**
* MyBatis 允许你在映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：
*
* Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
* ParameterHandler (getParameterObject, setParameters)
* ResultSetHandler (handleResultSets, handleOutputParameters)
* StatementHandler (prepare, parameterize, batch, update, query)
* 这些类中方法的细节可以通过查看每个方法的签名来发现，或者直接查看 MyBatis 发行包中的源代码。 如果你想做的不仅仅是监控方法的调用，那么你最好相当了解要重写的方法的行为。 因为在试图修改或重写已有方法的行为时，很可能会破坏 MyBatis 的核心模块。 这些都是更底层的类和方法，所以使用插件的时候要特别当心。
*
* 通过 MyBatis 提供的强大机制，使用插件是非常简单的，只需实现 Interceptor 接口，并指定想要拦截的方法签名即可
*/
//@Intercepts({@Signature(
// type= Executor.class,
// method = "query",
// args = {StatementHandler.class, Object.class, RowBounds.class, ResultHandler.class})})
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})})
public class SQLInterceptor implements Interceptor {
private Properties properties = new Properties();
public List<String> getInsertPropertiesName(List<Map<String, Object>> properties) {
List<String> list = new ArrayList<>();
properties.forEach(data -> data.keySet()
.stream()
.filter(e -> e.equals("columnName"))
.forEach(e -> list.add((String) data.get("columnName"))));
return list;
}
public void setInsertProperties(List<Map<String, Object>> properties, String columnName, Object value) {
properties.forEach(element -> element.forEach((k, v) -> {
if (k.equals("columnName") && element.get(k).equals(columnName)) {
element.put("columnValue", value);
element.put("columnName", columnName);
}
}));
}
@Override
public Object intercept(Invocation invocation) throws Throwable {
// implement pre processing if need
List<Map<String, Object>> insertProperties = new ArrayList<>();
Map<String, Object> nameProperties = new HashMap<>();
nameProperties.put("columnName", "name");
nameProperties.put("columnValue", "baby");
nameProperties.put("expr", "and");
insertProperties.add(nameProperties);
Map<String, Object> namePropertiesOr = new HashMap<>();
namePropertiesOr.put("columnName", "id");
namePropertiesOr.put("columnValue", "1");
namePropertiesOr.put("expr", "or");
insertProperties.add(namePropertiesOr);
// BoundSql boundSql = ((MappedStatement)invocation.getArgs()[0]).getBoundSql(invocation.getArgs()[1]);
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
// 获取传入的参数
Object parameterMappings = statementHandler.getBoundSql().getParameterObject();
if (parameterMappings instanceof Map) {
Map parameterMappingsConvert = (Map) parameterMappings;
getInsertPropertiesName(insertProperties).forEach(e -> {
Object value = parameterMappingsConvert.get(e);
if (value != null) { // 如果传参值不为空就覆盖配置值
setInsertProperties(insertProperties, e, value);
}
});
}
MetaObject metaObject = MetaObject
.forObject(statementHandler, SystemMetaObject.DEFAULT_OBJECT_FACTORY, SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,
new DefaultReflectorFactory());
BoundSql boundSql = statementHandler.getBoundSql();
SQLStatementParser sqlParser = SQLParserUtils.createSQLStatementParser(boundSql.getSql(), DbType.MYSQL.getValue());
SQLStatement stmt = sqlParser.parseStatementList().get(0);
System.out.println("Origin SQL is:" + boundSql.getSql());
System.out.println("++++++++++++++++++++++");
if (stmt instanceof SQLSelectStatement) {
// ((SQLSelectStatement) stmt).addWhere(sqlExpr);
// convert conditions to 'and' statement
StringBuilder constraintsBuffer = new StringBuilder();
boolean first = true;
for (Map<String, Object> data : insertProperties) {
if (String.valueOf(data.get("expr")).equalsIgnoreCase("and")) {
if (!first) {
constraintsBuffer.append(" AND ");
}
constraintsBuffer.append(String.format(" %s = '%s' ", data.get("columnName"), data.get("columnValue")));
} else if (String.valueOf(data.get("expr")).equalsIgnoreCase("or")) {
if (!first) {
constraintsBuffer.append(" OR ");
}
constraintsBuffer.append(String.format(" %s = '%s' ", data.get("columnName"), data.get("columnValue")));
}
first = false;
}
SQLExprParser constraintsParser = SQLParserUtils.createExprParser(constraintsBuffer.toString(), JdbcUtils.MYSQL);
SQLExpr constraintsExpr = constraintsParser.expr();
SQLSelectStatement selectStmt = (SQLSelectStatement) stmt;
// 拿到SQLSelect 通过在这里打断点看对象我们可以看出这是一个树的结构
SQLSelect sqlselect = selectStmt.getSelect();
SQLSelectQueryBlock query = (SQLSelectQueryBlock) sqlselect.getQuery();
SQLExpr whereExpr = query.getWhere();
// 修改where表达式
if (whereExpr == null) {
query.setWhere(constraintsExpr);
} else {
SQLBinaryOpExpr newWhereExpr = new SQLBinaryOpExpr(
whereExpr, SQLBinaryOperator.BooleanAnd, constraintsExpr);
query.setWhere(newWhereExpr);
}
sqlselect.setQuery(query);
String sql = sqlselect.toString();
//通过反射修改sql语句
Field field = boundSql.getClass().getDeclaredField("sql");
field.setAccessible(true);
field.set(boundSql, sql);
System.out.println("modify sql is:" + sql);
}
// implement post processing if need
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
return Interceptor.super.plugin(target);
}
@Override
public void setProperties(Properties properties) {
this.properties = properties;
}
}
可以看到上面使用了反射去设置boundsql.sql，有可能有同学会问这样会不会触发JVM优化修改不了这个
final String属性。这里我下一个结论是可以的，为了解释这个问题我写了端代码帮助理解：
package base;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
public class FinalPropertyModify {
private final String a = "123";
private final String ab;
public FinalPropertyModify(String ab) {
this.ab = ab;
}
public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, NoSuchFieldException {
// 直接赋值初始化
FinalPropertyModify finalPropertyModify = new FinalPropertyModify("123");
Field a = FinalPropertyModify.class.getDeclaredField("a");
a.setAccessible(true);
a.set(finalPropertyModify, "12345");
// 构造函数初始化
Field ab = FinalPropertyModify.class.getDeclaredField("ab");
ab.setAccessible(true);
ab.set(finalPropertyModify, "123456");
System.out.println("==================反射获取==================");
System.out.println(a.get(finalPropertyModify));
System.out.println(ab.get(finalPropertyModify));
System.out.println("==================直接获取==================");
System.out.println(finalPropertyModify.a);
System.out.println(finalPropertyModify.ab);
}
}
最终输出结果为：
可以看到如果是直接赋值进行初始化final属性的话，会被JVM给优化掉，如果使用的是构造函数进行初始化属性是不是触发JVM优化的。我们再看一下boundsql类的属性定义，很显然sql属性是在构造函数中进行初始化的。我们可以大胆的去modify sql，但一定要注意不能修改成错误的SQL和一定要考虑安全问题，mybatis没有提供sql的修改方法也是考虑这一点，可能会不安全。
public class BoundSql {
// 我们要修改的SQL属性
private final String sql;
private final List<ParameterMapping> parameterMappings;
private final Object parameterObject;
private final Map<String, Object> additionalParameters;
private final MetaObject metaParameters;
public BoundSql(Configuration configuration, String sql, List<ParameterMapping> parameterMappings, Object parameterObject) {
this.sql = sql;
this.parameterMappings = parameterMappings;
this.parameterObject = parameterObject;
this.additionalParameters = new HashMap<>();
this.metaParameters = configuration.newMetaObject(additionalParameters);
}
public String getSql() {
return sql;
}
public List<ParameterMapping> getParameterMappings() {
return parameterMappings;
}
public Object getParameterObject() {
return parameterObject;
}
public boolean hasAdditionalParameter(String name) {
String paramName = new PropertyTokenizer(name).getName();
return additionalParameters.containsKey(paramName);
}
public void setAdditionalParameter(String name, Object value) {
metaParameters.setValue(name, value);
}
public Object getAdditionalParameter(String name) {
return metaParameters.getValue(name);
}
}
UserMapper.xml
很简单的一个SQL
DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.allens.mybatis.mappers.UserMapper">
<select id="selectUsers" parameterType="int" resultType="com.allens.mybatis.model.User">
select * from user where id = 1 limit ${pageSize}
select>
mapper>
测试
运行成功：
