mybatis 拦截器，改变默认行为

 页面输入：男，数据库保存male，女，数据库保存为female。

使用interceptor，typeHandler

package cn.dcr.mybatis.util;

import java.util.Properties;

import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;

import com.test.pojos.User;

@Intercepts({
		@Signature(type = Executor.class, method = "update", args = {
				MappedStatement.class, Object.class }),
		@Signature(type = Executor.class, method = "query", args = {
				MappedStatement.class, Object.class, RowBounds.class,
				ResultHandler.class }) })
public class MyInterceptor implements Interceptor {

	private static final String R_FEMALE = "女";

	private static final String R_MALE = "男";

	private static final String FEMALE = "female";

	private static final String MALE = "male";
	private Properties properties;

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.apache.ibatis.plugin.Interceptor#intercept(org.apache.ibatis.plugin
	 * .Invocation)
	 */
	public Object intercept(Invocation invocation) throws Throwable {

		MappedStatement mappedStatement = (MappedStatement) invocation
				.getArgs()[0];
		String sqlId = mappedStatement.getId();
		String namespace = sqlId.substring(0, sqlId.indexOf('.'));
		Executor exe = (Executor) invocation.getTarget();
		String methodName = invocation.getMethod().getName();

		if (methodName.equals("query")) {
				Object parameter = invocation.getArgs()[1];
				RowBounds rowBounds = (RowBounds) invocation.getArgs()[2];
				 
		}
		else if(methodName.equals("update")){
			Object parameter = invocation.getArgs()[1];
			if(parameter instanceof User)
				((User)parameter).setGender(saveValueToDb(((User)parameter).getGender()));
			
		}
		return invocation.proceed();

	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.apache.ibatis.plugin.Interceptor#plugin(java.lang.Object)
	 */
	public Object plugin(Object target) {
		return Plugin.wrap(target, this);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.apache.ibatis.plugin.Interceptor#setProperties(java.util.Properties)
	 */
	public void setProperties(Properties properties) {
		this.properties = properties;

	}
	/**插入数据库
	 * @param value
	 * @return
	 */
	private String saveValueToDb(String value) {
		if (value.equals(R_FEMALE)) {
			return FEMALE;
		} else if (value.equals(R_MALE)) {
			return MALE;
		} else {
			throw new IllegalArgumentException("数据库异常!" + value);
		}
	}

}

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

 mybatis 拦截器好像只能使用注解，而且对于接口Executor，method只定义了update，query，flushStatements，commit，rollback，createCacheKey，isCached，clearLocalCache，deferLoad，getTransaction，close，isClosed这几个方法，没有delete和insert方法。

具体详见：

package org.apache.ibatis.executor;

import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

import java.sql.SQLException;
import java.util.List;

public interface Executor {

  ResultHandler NO_RESULT_HANDLER = null;

  int update(MappedStatement ms, Object parameter) throws SQLException;

  List query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;

  List<BatchResult> flushStatements() throws SQLException;

  void commit(boolean required) throws SQLException;

  void rollback(boolean required) throws SQLException;

  CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds);

  boolean isCached(MappedStatement ms, CacheKey key);

  void clearLocalCache();

  void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key);

  Transaction getTransaction();

  void close(boolean forceRollback);
  
  boolean isClosed();

}

    当我疑惑为什么mybatis没有在insert和delete的时候拦截呢？

看到了mybatis googleCode上的issue16。

Reporter:  	 Eli Kizhnerman

The iBatis plugin does not seem to be resolving the target methods to
intercept properly. An interceptor that is defined to intercept only
updates is also executed on inserts.

I have the following definition:
@Intercepts({@Signature(
        type=Executor.class,
        method="update",
        args={MappedStatement.class,Object.class})})
public class UpdateInterceptor implements Interceptor {
...
}

In Plugin.invoke you have the following code:

      Set<Method> methods = signatureMap.get(method.getDeclaringClass());
      if (methods != null && methods.contains(method)) {
        return interceptor.intercept(new Invocation(target, method, args));
      }

DefaultSqlSession.insert internally calls an update method:

  public int insert(String statement, Object parameter) {
    return update(statement, parameter);
  }

I suspect that the Method that is being passed to plugin.invoke is actually
the update method and therefore the interceptor is executed.

  原来在DefaultSqlSession的insert，delete方法也是调用了update方法。

public int insert(String statement, Object parameter) {
    return update(statement, parameter);
  }

public int delete(String statement, Object parameter) {
    return update(statement, wrapCollection(parameter));
  }

   mybatis太不厚道了，它的文档也没有具体的说明。

    有人提出这是个bug，不过mybatis没有承认。

Clinton Begin added a comment - 10/Dec/09 03:58 PM
Executor only has update and query methods. Thus inserts and deletes are also
considered updates. It sounds like to do what you want, we need another interception
point, at the session level. You can do so right now with a proxy class between the
SqlSession interface and the default implementation.
[ Show » ]
Clinton Begin added a comment - 10/Dec/09 03:58 PM Executor only has update and query
methods. Thus inserts and deletes are also considered updates. It sounds like to do
what you want, we need another interception point, at the session level. You can do
so right now with a proxy class between the SqlSession interface and the default
implementation.

[ Permalink | Delete | « Hide ]
Eli Kizhnerman added a comment - 11/Dec/09 12:28 PM
This is not working the way I expected it but that it is not a bug. I can get what I
need from the MappedStatement SqlCommandType.

package cn.dcr.mybatis.util;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;

/**自定义typeHandler<br/>
 * 1 插入数据库，男转为male
 * 2 查询，maile转为男
 * @author Administrator
 *
 */
public class GenderTypeHandlerCallback extends BaseTypeHandler<String> {

	private static final String R_FEMALE = "女";

	private static final String R_MALE = "男";

	private static final String FEMALE = "female";

	private static final String MALE = "male";

	@Override
	public String getNullableResult(CallableStatement cs, int columnIndex)
			throws SQLException {

		return cs.getString(columnIndex);
	}

	@Override
	public String getNullableResult(ResultSet rs, String columnName)
			throws SQLException {
		String t = rs.getString(columnName);
		return converSex(t);
	}

	@Override
	public void setNonNullParameter(PreparedStatement preparedStatement, int i,
			String str, JdbcType jdbcType) throws SQLException {

		preparedStatement.setString(i, saveValueToDb(str));

	}

	/**插入数据库
	 * @param value
	 * @return
	 */
	private String saveValueToDb(String value) {
		if (value.equals(R_FEMALE)) {
			return FEMALE;
		} else if (value.equals(R_MALE)) {
			return MALE;
		} else {
			throw new IllegalArgumentException("数据库异常!" + value);
		}
	}
	
	/** 从数据库读出
	 * @param value
	 * @return
	 */
	private String converSex(String value){
		if (value.equals(FEMALE)) {
			return R_FEMALE;
		} else if (value.equals(MALE)) {
			return R_MALE;
		} else {
			throw new IllegalArgumentException("数据库异常!" + value);
		}
	}

}

  在自定义typeHandler的getNullableResult方法中调整自己的结果集，可以说是在sql执行后，IOC的理论叫后置通知，interceptor应该是前置通知。

@Override
	public String getNullableResult(ResultSet rs, String columnName)
			throws SQLException {
		String t = rs.getString(columnName);
		return converSex(t);
	}

 在typeHandler的setNonNullParameter，应该是参数传入前转换参数的功能，但是实际操作中没有被调用，不知道为什么。

@Override
	public void setNonNullParameter(PreparedStatement preparedStatement, int i,
			String str, JdbcType jdbcType) throws SQLException {

		preparedStatement.setString(i, saveValueToDb(str));

	}

 以上是对mybatis 的切入点的实践。总体感觉和struts2的拦截器比，还有差距，至少我理解struts2的拦截器比理解它的要快。