Spring MVC Interceptor

What is an interceptor

The interceptor is SpringMvc Functions provided by the framework

It can be before or after the controller method runs ( There are other special occasions ) A specific interface for processing or processing requests

Frequently asked questions : The difference between filters and interceptors

Both filters and interceptors can add additional code before and after the controller method runs , Realization aop effect

  • Different providers

    • The filter is made of javaEE Provided
    • The interceptor is SpringMvc Provided

  • Different goals

    • The filter has a broader purpose : It can be used in all processes that request the current server resources
    • The interceptor has a single target : It can only be used in the process where the request target is the current server controller

  • Different functional strength

    • The filter is native JavaEE The function of , Weak function , Can't handle it directly Spring Contents and objects in the container
    • The interceptor is SpringMvc Framework provided , So born with Spring Containers have better compatibility , Can be operated directly Spring Objects in the container , And the interceptor has better processing of parameter return value than the filter , There are also more opportunities to run

  • Conclusion

    If the target of the request can be determined to be a controller method , Give priority to interceptors

    If the target of the request may be other static resources , Then you need to use filters

Detailed operation , See teacher Cheng's notes

Mybatis Interceptor

brief introduction :

Mybatis A function provided by the framework

In the Mapper The ability to add additional code before or after the interface method runs

Before, we set , Implement the sql Statement output to the console , It is implemented by interceptors

We can also simply do a similar demonstration

First , To successfully intercept Mybatis in mapper Running sql sentence

You need to be in Spring Set relevant codes in

step 1: Write interceptors 

// Mybatis Interceptor test class 

@Slf4j

// Mybatis Annotations for interceptor configuration declaration 

//  You can configure to intercept multiple jdbc Objects in the 

@Intercepts({@Signature(

        type = StatementHandler.class,

        method = "prepare",

        args = {Connection.class,Integer.class}

)})

public class MyInterceptor implements Interceptor {

    // Mybatis Interceptor method 

    // invocation  It is the goal to run ( Here is the sql sentence )

    @Override

    public Object intercept(Invocation invocation) throws Throwable {

        log.info(" Enter the interceptor , Ready to intercept sql sentence ");

        //  From parameter invocation Get the to run sql Statement object BoundSql

        BoundSql boundSql=((StatementHandler)invocation.getTarget())

                                        .getBoundSql();

        //  from boundSql In order to get sql sentence 

        String sql=boundSql.getSql();

        log.info(" The original to run sql Statement for :{}",sql);

        //  Next, you can sql Statement changes 

        sql=sql+" and 1=1";

        log.info(" After the change sql sentence :{}",sql);

        //  Forced assignment with reflection , take boundSql Medium sql Property changes 

        reflectUpdateSql(boundSql,"sql",sql);

        return invocation.proceed();

    }

    //  You need to define a method , To be able to sql Statement to rewrite 

    //  however sql The statement is already in invocation We need to use reflection , Rewrite the attributes 

    private void reflectUpdateSql(BoundSql boundSql,

                                  String attrName,String attrValue)

            throws NoSuchFieldException, IllegalAccessException {

        //  The goal of this method is to boundSql Object's sql Forced assignment assignment 

        //  Attribute class of reflection 

        Field field=boundSql.getClass().getDeclaredField(attrName);

        //  Setting properties forces assignment   After setting, it is not a private property 

        field.setAccessible(true);

        //  Assign the prepared value to this attribute 

        field.set(boundSql,attrValue);

    }

    // User  class    User Class has a private attribute password   No, getset Method 

    //  Reflection can be forced to password Property assignment 

    // BoundSql amount to User object 

    // attrName amount to password attribute 

    // attrValue Equivalent to the value of the attribute we want to force payment 

}

step 2:

Set the Interceptor at SpringBoot Make it effective under the framework

config In bag 

// This class is configuration Mybatis Interceptor effective configuration class 

@Configuration

//  To configure Mybatis Fixed code for interceptors to take effect 

@AutoConfigureAfter(MybatisAutoConfiguration.class)

public class InterceptorConfig {

    //  get Mybatis Session manager for 

    // Mybatis Session manager is the core class that performs connection operations to the database 

    @Autowired

    private List<SqlSessionFactory> sqlSessionFactoryList;

    //  The following method is to Mybatis All connections in the session manager are associated with the interceptors we wrote , Make the interceptor work 

    @PostConstruct

    public void addInterceptors(){

        //  Instantiate the interceptor we wrote 

        Interceptor interceptor=new MyInterceptor();

        for (SqlSessionFactory factory:sqlSessionFactoryList){

            factory.getConfiguration().addInterceptor(interceptor);

        }

    }

}

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