目錄一、攔截對(duì)象和接口實(shí)現(xiàn)示例二、攔截器注冊(cè)的三種方式1.XML注冊(cè)2.配置類注冊(cè)3.注解方式三、ParameterHandler參數(shù)改寫(xiě)-修改時(shí)間和修改人統(tǒng)一插入四、通過(guò)StatementHandler改寫(xiě)SQL一、攔截對(duì)象和接口實(shí)現(xiàn)示例

MyBatis攔截器的作用是在于Dao到DB中間進(jìn)行額外的處理。大部分情況下通過(guò)mybatis的xml配置sql都可以達(dá)到想要的DB操作效果，然而存在一些類似或者相同的查詢條件或者查詢要求，這些可以通過(guò)攔截器的實(shí)現(xiàn)可以提升開(kāi)發(fā)效率，比如：分頁(yè)、插入和更新時(shí)間/人、數(shù)據(jù)權(quán)限、SQL監(jiān)控日志等。

Mybatis支持四種對(duì)象攔截Executor、StatementHandler、PameterHandler和ResultSetHandler Executor：攔截執(zhí)行器的方法。 StatementHandler：攔截Sql語(yǔ)法構(gòu)建的處理。 ParameterHandler：攔截參數(shù)的處理。 ResultHandler：攔截結(jié)果集的處理。

public interface Executor { ResultHandler NO_RESULT_HANDLER = null; int update(MappedStatement var1, Object var2) throws SQLException; <E> List<E> query(MappedStatement var1, Object var2, RowBounds var3, ResultHandler var4, CacheKey var5, BoundSql var6) throws SQLException; <E> List<E> query(MappedStatement var1, Object var2, RowBounds var3, ResultHandler var4) throws SQLException; <E> Cursor<E> queryCursor(MappedStatement var1, Object var2, RowBounds var3) throws SQLException; List<BatchResult> flushStatements() throws SQLException; void commit(boolean var1) throws SQLException; void rollback(boolean var1) throws SQLException; CacheKey createCacheKey(MappedStatement var1, Object var2, RowBounds var3, BoundSql var4); boolean isCached(MappedStatement var1, CacheKey var2); void clearLocalCache(); void deferLoad(MappedStatement var1, MetaObject var2, String var3, CacheKey var4, Class<?> var5); Transaction getTransaction(); void close(boolean var1); boolean isClosed(); void setExecutorWrapper(Executor var1);}public interface StatementHandler { Statement prepare(Connection var1, Integer var2) throws SQLException; void parameterize(Statement var1) throws SQLException; void batch(Statement var1) throws SQLException; int update(Statement var1) throws SQLException; <E> List<E> query(Statement var1, ResultHandler var2) throws SQLException; <E> Cursor<E> queryCursor(Statement var1) throws SQLException; BoundSql getBoundSql(); ParameterHandler getParameterHandler();}public interface ParameterHandler { Object getParameterObject(); void setParameters(PreparedStatement var1) throws SQLException;}public interface ResultHandler<T> { void handleResult(ResultContext<? extends T> var1);}

攔截的執(zhí)行順序是Executor->StatementHandler->ParameterHandler->ResultHandler

MyBatis提供的攔截器接口：

public interface Interceptor { Object intercept(Invocation var1) throws Throwable; default Object plugin(Object target) {return Plugin.wrap(target, this); } default void setProperties(Properties properties) {}}

Object intercept方法用于攔截器的實(shí)現(xiàn)；

Object plugin方法用于判斷執(zhí)行攔截器的類型；

void setProperties方法用于獲取配置項(xiàng)的屬性。

攔截對(duì)象和攔截器接口的結(jié)合，自定義的攔截器類需要實(shí)現(xiàn)攔截器接口，并通過(guò)注解@Intercepts和參數(shù)@Signature來(lái)聲明要攔截的對(duì)象。

@Signature參數(shù)type是攔截對(duì)象，method是攔截的方法，即上面的四個(gè)類對(duì)應(yīng)的方法，args是攔截方法對(duì)應(yīng)的參數(shù)（方法存在重載因此需要指明參數(shù)個(gè)數(shù)和類型）

@Intercepts可以有多個(gè)@Signature，即一個(gè)攔截器實(shí)現(xiàn)類可以同時(shí)攔截多個(gè)對(duì)象及方法，示例如下：

Executor->intercept StatementHandler->intercept ParameterHandler->intercept ResultHandler->intercept

@Intercepts({@Signature(type = Executor.class,method = 'query',args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})public class SelectPlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof Executor) { System.out.println('SelectPlugin');}return invocation.proceed(); } @Override public Object plugin(Object target) {if (target instanceof Executor) { return Plugin.wrap(target, this);}return target; } @Override public void setProperties(Properties properties) {}}@Intercepts({@Signature(type = StatementHandler.class, method = 'prepare', args = {Connection.class, Integer.class})})public class StatementPlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof StatementHandler) { System.out.println('StatementPlugin');}return invocation.proceed(); } @Override public Object plugin(Object target) {if (target instanceof StatementHandler) { return Plugin.wrap(target, this);}return target; } @Override public void setProperties(Properties properties) {}}@Intercepts({@Signature(type = ParameterHandler.class,method = 'setParameters',args = {PreparedStatement.class})})public class ParameterPlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof ParameterHandler) { System.out.println('ParameterPlugin');}return invocation.proceed(); } @Override public Object plugin(Object target) {if (target instanceof ParameterHandler) { return Plugin.wrap(target, this);}return target; } @Override public void setProperties(Properties properties) {}}@Intercepts({@Signature(type = ResultHandler.class,method = 'handleResult',args = {ResultContext.class})})public class ResultPlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof ResultHandler) { System.out.println('ResultPlugin');}return invocation.proceed(); } @Override public Object plugin(Object target) {if (target instanceof ResultHandler) { return Plugin.wrap(target, this);}return target; } @Override public void setProperties(Properties properties) {}}二、攔截器注冊(cè)的三種方式

前面介紹了Mybatis的攔截對(duì)象及其接口的實(shí)現(xiàn)方式，那么在項(xiàng)目中如何注冊(cè)攔截器呢？本文中給出三種注冊(cè)方式。

1.XML注冊(cè)

xml注冊(cè)是最基本的方式，是通過(guò)在Mybatis配置文件中plugins元素來(lái)進(jìn)行注冊(cè)的。一個(gè)plugin對(duì)應(yīng)著一個(gè)攔截器，在plugin元素可以指定property子元素，在注冊(cè)定義攔截器時(shí)把對(duì)應(yīng)攔截器的所有property通過(guò)Interceptor的setProperties方法注入給攔截器。因此攔截器注冊(cè)xml方式如下：

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE configuration PUBLIC '-//mybatis.org//DTD Config 3.0//EN' 'http://mybatis.org/dtd/mybatis-3-config.dtd'><configuration> <!-- ...... --> <plugins> <plugin interceptor='com.tiantian.mybatis.interceptor.MyInterceptor'> <property name='prop1' value='prop1'/> <property name='prop2' value='prop2'/> </plugin> </plugins> <!-- ...... --></configuration>2.配置類注冊(cè)

配置類注冊(cè)是指通過(guò)Mybatis的配置類中聲明注冊(cè)攔截器，配置類注冊(cè)也可以通過(guò)Properties類給Interceptor的setProperties方法注入?yún)?shù)。具體參考如下：

@Configurationpublic class MyBatisConfig { @Bean public String MyBatisInterceptor(SqlSessionFactory sqlSessionFactory) {UpdatePlugin executorInterceptor = new UpdatePlugin();Properties properties = new Properties();properties.setProperty('prop1', 'value1');// 給攔截器添加自定義參數(shù)executorInterceptor.setProperties(properties);sqlSessionFactory.getConfiguration().addInterceptor(executorInterceptor);sqlSessionFactory.getConfiguration().addInterceptor(new StatementPlugin());sqlSessionFactory.getConfiguration().addInterceptor(new ResultPlugin());sqlSessionFactory.getConfiguration().addInterceptor(new ParameterPlugin());// sqlSessionFactory.getConfiguration().addInterceptor(new SelectPlugin());return 'interceptor'; } // 與sqlSessionFactory.getConfiguration().addInterceptor(new SelectPlugin());效果一致 @Bean public SelectPlugin SelectInterceptor() {SelectPlugin interceptor = new SelectPlugin();Properties properties = new Properties();// 調(diào)用properties.setProperty方法給攔截器設(shè)置自定義參數(shù)interceptor.setProperties(properties);return interceptor; }}3.注解方式

通過(guò)@Component注解方式是最簡(jiǎn)單的方式，在不需要轉(zhuǎn)遞自定義參數(shù)時(shí)可以使用，方便快捷。

@Component@Intercepts({@Signature(type = Executor.class,method = 'query',args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})public class SelectPlugin implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof Executor) { System.out.println('SelectPlugin');}return invocation.proceed(); } @Override public Object plugin(Object target) {if (target instanceof Executor) { return Plugin.wrap(target, this);}return target; } @Override public void setProperties(Properties properties) { }}三、ParameterHandler參數(shù)改寫(xiě)-修改時(shí)間和修改人統(tǒng)一插入

針對(duì)具體的攔截器實(shí)現(xiàn)進(jìn)行描述。日常編碼需求中會(huì)碰到修改時(shí)需要插入修改的時(shí)間和人員，如果要用xml的方式去寫(xiě)非常麻煩，而通過(guò)攔截器的方式可以快速實(shí)現(xiàn)全局的插入修改時(shí)間和人員。先看代碼：

@Component@Intercepts({@Signature(type = ParameterHandler.class, method = 'setParameters', args = {PreparedStatement.class}),})public class MyBatisInterceptor implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {// 參數(shù)代理if (invocation.getTarget() instanceof ParameterHandler) { System.out.println('ParameterHandler'); // 自動(dòng)添加操作員信息 autoAddOperatorInfo(invocation);}return invocation.proceed(); } @Override public Object plugin(Object target) {return Plugin.wrap(target, this); } @Override public void setProperties(Properties properties) { } /** * 自動(dòng)添加操作員信息 * * @param invocation 代理對(duì)象 * @throws Throwable 異常 */ private void autoAddOperatorInfo(Invocation invocation) throws Throwable {System.out.println('autoInsertCreatorInfo');// 獲取代理的參數(shù)對(duì)象ParameterHandlerParameterHandler ph = (ParameterHandler) invocation.getTarget();// 通過(guò)MetaObject獲取ParameterHandler的反射內(nèi)容MetaObject metaObject = MetaObject.forObject(ph,SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,new DefaultReflectorFactory());// 通過(guò)MetaObject反射的內(nèi)容獲取MappedStatementMappedStatement mappedStatement = (MappedStatement) metaObject.getValue('mappedStatement');// 當(dāng)sql類型為INSERT或UPDATE時(shí)，自動(dòng)插入操作員信息if (mappedStatement.getSqlCommandType() == SqlCommandType.INSERT ||mappedStatement.getSqlCommandType() == SqlCommandType.UPDATE) { // 獲取參數(shù)對(duì)象 Object obj = ph.getParameterObject(); if (null != obj) {// 通過(guò)反射獲取參數(shù)對(duì)象的屬性Field[] fields = obj.getClass().getDeclaredFields();// 遍歷參數(shù)對(duì)象的屬性for (Field f : fields) { // 如果sql是INSERT,且存在createdAt屬性 if ('createdAt'.equals(f.getName()) && mappedStatement.getSqlCommandType() == SqlCommandType.INSERT) {// 設(shè)置允許訪問(wèn)反射屬性f.setAccessible(true);// 如果沒(méi)有設(shè)置createdAt屬性，則自動(dòng)為createdAt屬性添加當(dāng)前的時(shí)間if (null == f.get(obj)) { // 設(shè)置createdAt屬性為當(dāng)前時(shí)間 f.set(obj, LocalDateTime.now());} } // 如果sql是INSERT,且存在createdBy屬性 if ('createdBy'.equals(f.getName()) && mappedStatement.getSqlCommandType() == SqlCommandType.INSERT) {// 設(shè)置允許訪問(wèn)反射屬性f.setAccessible(true);// 如果沒(méi)有設(shè)置createdBy屬性，則自動(dòng)為createdBy屬性添加當(dāng)前登錄的人員if (null == f.get(obj)) { // 設(shè)置createdBy屬性為當(dāng)前登錄的人員 f.set(obj, 0);} } // sql為INSERT或UPDATE時(shí)均需要設(shè)置updatedAt屬性 if ('updatedAt'.equals(f.getName())) {f.setAccessible(true);if (null == f.get(obj)) { f.set(obj, LocalDateTime.now());} } // sql為INSERT或UPDATE時(shí)均需要設(shè)置updatedBy屬性 if ('updatedBy'.equals(f.getName())) {f.setAccessible(true);if (null == f.get(obj)) { f.set(obj, 0);} }}// 通過(guò)反射獲取ParameterHandler的parameterObject屬性Field parameterObject = ph.getClass().getDeclaredField('parameterObject');// 設(shè)置允許訪問(wèn)parameterObject屬性parameterObject.setAccessible(true);// 將上面設(shè)置的新參數(shù)對(duì)象設(shè)置到ParameterHandler的parameterObject屬性parameterObject.set(ph, obj); }} }}

攔截器的接口實(shí)現(xiàn)參考前文，這里著重介紹autoAddOperatorInfo方法里的相關(guān)類。

1.ParameterHandler

接口源碼：

public interface ParameterHandler { Object getParameterObject(); void setParameters(PreparedStatement var1) throws SQLException; }

提供兩個(gè)方法：

getParameterObject是獲取參數(shù)對(duì)象，可能存在null，需要注意null指針。

setParameters是控制如何設(shè)置SQL參數(shù)，即sql語(yǔ)句中配置的java對(duì)象和jdbc類型對(duì)應(yīng)的關(guān)系，例如#{id,jdbcType=INTEGER}，id默認(rèn)類型是javaType=class java.lang.Integer。

該接口有一個(gè)默認(rèn)的實(shí)現(xiàn)類，源碼如下：

public class DefaultParameterHandler implements ParameterHandler { private final TypeHandlerRegistry typeHandlerRegistry; private final MappedStatement mappedStatement; private final Object parameterObject; private final BoundSql boundSql; private final Configuration configuration; public DefaultParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {this.mappedStatement = mappedStatement;this.configuration = mappedStatement.getConfiguration();this.typeHandlerRegistry = mappedStatement.getConfiguration().getTypeHandlerRegistry();this.parameterObject = parameterObject;this.boundSql = boundSql; } public Object getParameterObject() {return this.parameterObject; } public void setParameters(PreparedStatement ps) {ErrorContext.instance().activity('setting parameters').object(this.mappedStatement.getParameterMap().getId());List<ParameterMapping> parameterMappings = this.boundSql.getParameterMappings();if (parameterMappings != null) { for(int i = 0; i < parameterMappings.size(); ++i) {ParameterMapping parameterMapping = (ParameterMapping)parameterMappings.get(i);if (parameterMapping.getMode() != ParameterMode.OUT) { String propertyName = parameterMapping.getProperty(); Object value; if (this.boundSql.hasAdditionalParameter(propertyName)) {value = this.boundSql.getAdditionalParameter(propertyName); } else if (this.parameterObject == null) {value = null; } else if (this.typeHandlerRegistry.hasTypeHandler(this.parameterObject.getClass())) {value = this.parameterObject; } else {MetaObject metaObject = this.configuration.newMetaObject(this.parameterObject);value = metaObject.getValue(propertyName); } TypeHandler typeHandler = parameterMapping.getTypeHandler(); JdbcType jdbcType = parameterMapping.getJdbcType(); if (value == null && jdbcType == null) {jdbcType = this.configuration.getJdbcTypeForNull(); } try {typeHandler.setParameter(ps, i + 1, value, jdbcType); } catch (SQLException | TypeException var10) {throw new TypeException('Could not set parameters for mapping: ' + parameterMapping + '. Cause: ' + var10, var10); }} }} }}

通過(guò)DefaultParameterHandler實(shí)現(xiàn)類我們知道通過(guò)ParameterHandler可以獲取到哪些屬性和方法，其中包括我們下面一個(gè)重要的類MappedStatement。

2.MappedStatement

MyBatis的mapper文件中的每個(gè)select/update/insert/delete標(biāo)簽會(huì)被解析器解析成一個(gè)對(duì)應(yīng)的MappedStatement對(duì)象，也就是一個(gè)MappedStatement對(duì)象描述一條SQL語(yǔ)句。MappedStatement對(duì)象屬性如下：

// mapper配置文件名 private String resource; // mybatis的全局信息，如jdbc private Configuration configuration; // 節(jié)點(diǎn)的id屬性加命名空間,如：com.example.mybatis.dao.UserMapper.selectByExample private String id; private Integer fetchSize; private Integer timeout; private StatementType statementType; private ResultSetType resultSetType; private SqlSource sqlSource; private Cache cache; private ParameterMap parameterMap; private List<ResultMap> resultMaps; private boolean flushCacheRequired; private boolean useCache; private boolean resultOrdered; // sql語(yǔ)句的類型：select、update、delete、insert private SqlCommandType sqlCommandType; private KeyGenerator keyGenerator; private String[] keyProperties; private String[] keyColumns; private boolean hasNestedResultMaps; private String databaseId; private Log statementLog; private LanguageDriver lang; private String[] resultSets;

在本例中通過(guò)MappedStatement對(duì)象的sqlCommandType來(lái)判斷當(dāng)前的sql類型是insert、update來(lái)進(jìn)行下一步的操作。

四、通過(guò)StatementHandler改寫(xiě)SQL

StatementHandler是用于封裝JDBC Statement操作，負(fù)責(zé)對(duì)JDBC Statement的操作，如設(shè)置參數(shù)，并將Statement結(jié)果集轉(zhuǎn)換成List集合。

實(shí)現(xiàn)代碼如下：

刪除注解標(biāo)記

@Target({ElementType.METHOD}) //表示注解的使用范圍@Retention(RetentionPolicy.RUNTIME) //注解的保存時(shí)間@Documented //文檔顯示public @interface DeletedAt { boolean has() default true;}

Dao層添加刪除注解，為false時(shí)不添加刪除標(biāo)志

@Mapper public interface AdminProjectDao { @DeletedAt(has = false) List<AdminProjectPo> selectProjects(AdminProjectPo po); }

攔截器通過(guò)刪除注解標(biāo)記判斷是否添加刪除標(biāo)志

@Component@Intercepts({@Signature(type = StatementHandler.class, method = 'prepare', args = {Connection.class, Integer.class}),})public class MyBatisInterceptor implements Interceptor { @Override public Object intercept(Invocation invocation) throws Throwable {if (invocation.getTarget() instanceof StatementHandler) { System.out.println('StatementHandler'); checkHasDeletedAtField(invocation);}return invocation.proceed(); } @Override public Object plugin(Object target) {return Plugin.wrap(target, this); } @Override public void setProperties(Properties properties) { } /** * 檢查查詢是否需要添加刪除標(biāo)志字段 * * @param invocation 代理對(duì)象 * @throws Throwable 異常 */ private void checkHasDeletedAtField(Invocation invocation) throws Throwable {System.out.println('checkHasDeletedAtField');StatementHandler statementHandler = (StatementHandler) invocation.getTarget();// 通過(guò)MetaObject訪問(wèn)對(duì)象的屬性MetaObject metaObject = MetaObject.forObject(statementHandler,SystemMetaObject.DEFAULT_OBJECT_FACTORY,SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,new DefaultReflectorFactory());// 獲取成員變量mappedStatementMappedStatement mappedStatement = (MappedStatement) metaObject.getValue('delegate.mappedStatement');// 如果sql類型是查詢if (mappedStatement.getSqlCommandType() == SqlCommandType.SELECT) { // 獲取刪除注解標(biāo)志 DeletedAt annotation = null; String id = mappedStatement.getId(); String className = id.substring(0, id.lastIndexOf('.')); String methodName = id.substring(id.lastIndexOf('.') + 1); Class<?> aClass = Class.forName(className); Method[] declaredMethods = aClass.getDeclaredMethods(); for (Method declaredMethod : declaredMethods) {declaredMethod.setAccessible(true);//方法名相同，并且注解是DeletedAtif (methodName.equals(declaredMethod.getName()) && declaredMethod.isAnnotationPresent(DeletedAt.class)) { annotation = declaredMethod.getAnnotation(DeletedAt.class);} } // 如果注解不存在或者注解為true（默認(rèn)為true） 則為mysql語(yǔ)句增加刪除標(biāo)志 if (annotation == null || annotation.has()) {BoundSql boundSql = statementHandler.getBoundSql();//獲取到原始sql語(yǔ)句String sql = boundSql.getSql();//通過(guò)反射修改sql語(yǔ)句Field field = boundSql.getClass().getDeclaredField('sql');field.setAccessible(true);String newSql = sql.replaceAll('9=9', '9=9 and deleted_at is null ');field.set(boundSql, newSql); }} }}

在SQL語(yǔ)句替換上需要能識(shí)別到要被替換的內(nèi)容，因此在xml的sql語(yǔ)句中加入特殊標(biāo)志'9=9',該標(biāo)志不影響原來(lái)SQL的執(zhí)行結(jié)果，不同的過(guò)濾條件可以設(shè)置不同的標(biāo)志，是一個(gè)比較巧妙的替換方式。

以上就是MyBatis攔截器的原理與使用的詳細(xì)內(nèi)容，更多關(guān)于MyBatis攔截器的資料請(qǐng)關(guān)注好吧啦網(wǎng)其它相關(guān)文章！