Mybatis外掛開發

冬眠的山谷發表於2019-06-10
MyBatis

前言

MyBatis開放使用者實現自己的外掛，從而對整個呼叫過程進行個性化擴充套件。

這是MyBatis整個呼叫流程的主要參與者。

我們可以對其中的一些過程進行攔截，新增自己的功能，比如重寫Sql新增分頁引數。

 

攔截的介面

MyBatis允許攔截的介面如下

Executor

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);
}

 

ParameterHandler

public interface ParameterHandler {
    Object getParameterObject();

    void setParameters(PreparedStatement var1) throws SQLException;
}

 

ResultSetHandler

public interface ResultSetHandler {
    <E> List<E> handleResultSets(Statement var1) throws SQLException;

    <E> Cursor<E> handleCursorResultSets(Statement var1) throws SQLException;

    void handleOutputParameters(CallableStatement var1) throws SQLException;
}

 

StatementHandler

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();
}

 

只要攔截器定義了攔截的介面和方法，後續呼叫該方法時，將會被攔截。

攔截器實現

如果要實現自己的攔截器，需要實現介面Interceptor


@Slf4j
@Intercepts(@Signature(type = Executor.class,
        method ="update",
        args ={MappedStatement.class,Object.class} ))
public class MyIntercetor implements Interceptor {


    @Override
    public Object intercept(Invocation invocation) throws Throwable {

        log.info("MyIntercetor ...");

        Object result = invocation.proceed();

        log.info("result = " + result);

        return result;
    }

    @Override
    public Object plugin(Object o) {
        return Plugin.wrap(o,this);
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

 

 

1. 攔截方法配置

@Intercepts(@Signature(type = Executor.class,
        method ="update",
        args ={MappedStatement.class,Object.class} ))

 

我們知道Java中方法的簽名包括所在的類，方法名稱，入參。 

@Signature定義方法簽名

type：攔截的介面，為上節定義的四個介面

method:攔截的介面方法

args:引數型別列表，需要和方法中定義的順序一致。

 

2. intercept(Invocation invocation)

public class Invocation {
    private final Object target;
    private final Method method;
    private final Object[] args;

    public Invocation(Object target, Method method, Object[] args) {
        this.target = target;
        this.method = method;
        this.args = args;
    }

    public Object getTarget() {
        return this.target;
    }

    public Method getMethod() {
        return this.method;
    }

    public Object[] getArgs() {
        return this.args;
    }

    public Object proceed() throws InvocationTargetException, IllegalAccessException {
        return this.method.invoke(this.target, this.args);
    }
}

 

通過Invocation可以獲取到被攔截的方法的呼叫物件，方法，引數。

proceed()用於繼續執行並獲得最終的結果。

這裡使用了設計模式中的責任鏈模式。

 

3.這裡不能返回null。

用於給被攔截的物件生成一個代理物件，並返回它。

@Override
    public Object plugin(Object o) {
        return Plugin.wrap(o,this);
    }

 可以看下wrap方法，其實現了JDK的介面InvocationHandler，也就是為傳入的target建立了一個代理物件。這裡使用了JDK動態代理方式。也可以自己實現其他代理方式，比如cglib.

    public class Plugin implements InvocationHandler {
    private final Object target;
    private final Interceptor interceptor;
    private final Map<Class<?>, Set<Method>> signatureMap;
　　 public static Object wrap(Object target, Interceptor interceptor) {
        Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
        Class<?> type = target.getClass();
        Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
        return interfaces.length > 0 ? Proxy.newProxyInstance(type.getClassLoader(), interfaces, new Plugin(target, interceptor, signatureMap)) : target;
    }

　　
　　public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
        Set<Method> methods = (Set)this.signatureMap.get(method.getDeclaringClass());
        return methods != null && methods.contains(method) ? this.interceptor.intercept(new Invocation(this.target, method, args)) : method.invoke(this.target, args);
    } catch (Exception var5) {
        throw ExceptionUtil.unwrapThrowable(var5);
    }
 }

}

由於使用了動態代理，方法執行時，將會被呼叫invoke方法，會先判斷是否設定了攔截器：methods != null && methods.contains(method)，

如果設定了攔截器，則呼叫攔截器this.interceptor.intercept(new Invocation(this.target, method, args))

否則直接呼叫method.invoke(this.target, args);

 

 

4.攔截器在執行前輸出"MyIntercetor ..."，在資料庫操作返回後輸出"result =xxx"

       log.info("MyIntercetor ...");

        Object result = invocation.proceed();

        log.info("result = " + result);

 

外掛實現完成！

 

測試

在Spring中引入很簡單。

第一種方式:

建立攔截器的bean

@Slf4j
@Configuration
public class IntercetorConfiguration {

    @Bean
    public MyIntercetor myIntercetor(){
        return new MyIntercetor();
    }

}

 

第二種方式

手動往Configuration中新增攔截器。

@Slf4j
@Configuration
public class IntercetorConfiguration {
  @Autowired
    private List<SqlSessionFactory> sqlSessionFactoryList;

    @PostConstruct
    public void addPageInterceptor() {
        MyIntercetor interceptor = new MyIntercetor();

        Iterator var3 = this.sqlSessionFactoryList.iterator();

        while(var3.hasNext()) {
            SqlSessionFactory sqlSessionFactory = (SqlSessionFactory)var3.next();
            sqlSessionFactory.getConfiguration().addInterceptor(interceptor);
        }

    }
}

 

由於上面定義的攔截器是攔截Executor的update方法，所以在執行insert,update,delete的操作時，將會被攔截。

本例子使用insert來測試。具體程式碼檢視：GitHub

2019-06-10 16:08:03.109  INFO 20410 --- [nio-8110-exec-1] c.m.user.dao.intercetor.MyIntercetor     : MyIntercetor ...

2019-06-10 16:08:03.166  INFO 20410 --- [nio-8110-exec-1] com.alibaba.druid.pool.DruidDataSource   : {dataSource-1} inited
2019-06-10 16:08:03.267 DEBUG 20410 --- [nio-8110-exec-1] o.m.s.t.SpringManagedTransaction         : JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@5cb1c36e] will not be managed by Spring
2019-06-10 16:08:03.274 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.dao.mapper.UserMapper.insertList   : ==>  Preparing: insert into user (name) values (?) , (?) , (?) 
2019-06-10 16:08:03.307 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.dao.mapper.UserMapper.insertList   : ==> Parameters: name:58(String), name:64(String), name:69(String)
2019-06-10 16:08:03.355 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.dao.mapper.UserMapper.insertList   : <==    Updates: 3
2019-06-10 16:08:03.358 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.d.m.U.insertList!selectKey         : ==>  Preparing: SELECT LAST_INSERT_ID() 
2019-06-10 16:08:03.358 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.d.m.U.insertList!selectKey         : ==> Parameters: 
2019-06-10 16:08:03.380 DEBUG 20410 --- [nio-8110-exec-1] c.m.u.d.m.U.insertList!selectKey         : <==      Total: 1


2019-06-10 16:08:03.381  INFO 20410 --- [nio-8110-exec-1] c.m.user.dao.intercetor.MyIntercetor     : result = 3

 

可以看到攔截器被呼叫了。

 

如果需要對查詢進行攔截，可以攔截以下方法，比如通過MappedStatement修改sql語句。

<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;

 

 

結束！！！！！

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