对IBatis分页的改进,使ibatis支持hibernate式的物理分页

      公司的大部分项目都开始使用IBatis 作为O/R Mapping了,但是在使用的过程中也发现了很多不方便和存在争议的地方,其中一个不方便的地方就是分页 ,目前的处理方式都是在sqlMap中写针对特定数据库的物理分页 Sql语句,对于oracle数据库都是在分页 的sql语句里面加上三层嵌套的sql语句,想了很多办法,都没能很好的避免这个问题,无意间在javaeye上看到了《使ibatis 支持hibernate式的物理分页 》这篇文章,可点进去已经被删除了 ,幸好google了一下有很多人已经收藏了,这里转载一下 ,以便再找不到了.

 

转载地址:http://www.blogjava.net/libin2722/articles/192504.html

 

一直以来ibatis 的分页 都是通过滚动ResultSet实现的，应该算是逻辑分页 吧。逻辑分页 虽然能很干净地独立于特定数据库，但效率在多数情况下不及特定数据库支持的物理分页 ，而hibernate的分页 则是直接组装sql，充分利用了特定数据库的分页 机制，效率相对较高。本文讲述的就是如何在不重新编译ibatis 源码的前提下，为ibatis 引入hibernate式的物理分页 机制。

基本思路就是找到ibatis 执行sql的地方，截获sql并重新组装sql。通过分析ibatis 源码知道，最终负责执行sql的类是 com.ibatis .sqlmap.engine.execution.SqlExecutor，此类没有实现任何接口，这多少有点遗憾，因为接口是相对稳定契约，非大的版本更新，接口一般是不会变的，而类就相对易变一些，所以这里的代码只能保证对当前版本（2.1.7）的ibatis 有效。下面是 SqlExecutor执行查询的方法：

/**
   * Long form of the method to execute a query
   *
   * @param request - the request scope
   * @param conn - the database connection
   * @param sql - the SQL statement to execute
   * @param parameters - the parameters for the statement
   * @param skipResults - the number of results to skip
   * @param maxResults - the maximum number of results to return
   * @param callback - the row handler for the query
   *
   * @throws SQLException - if the query fails
   */
  public
 
void
 executeQuery(RequestScope request, Connection conn, String sql, Object[] parameters,
                           int
 skipResults, 
int
 maxResults, RowHandlerCallback callback)
      throws
 SQLException {
    ErrorContext errorContext = request.getErrorContext();
    errorContext.setActivity("executing query"
);
    errorContext.setObjectId(sql);

    PreparedStatement ps = null
;
    ResultSet rs = null
;

    try
 {
      errorContext.setMoreInfo("Check the SQL Statement (preparation failed)."
);

      Integer rsType = request.getStatement().getResultSetType();
      if
 (rsType != 
null
) {
        ps = conn.prepareStatement(sql, rsType.intValue(), ResultSet.CONCUR_READ_ONLY);
      } else
 {
        ps = conn.prepareStatement(sql);
      }

      Integer fetchSize = request.getStatement().getFetchSize();
      if
 (fetchSize != 
null
) {
        ps.setFetchSize(fetchSize.intValue());
      }

      errorContext.setMoreInfo("Check the parameters (set parameters failed)."
);
      request.getParameterMap().setParameters(request, ps, parameters);

      errorContext.setMoreInfo("Check the statement (query failed)."
);

      ps.execute();
      rs = getFirstResultSet(ps);

      if
 (rs != 
null
) {
        errorContext.setMoreInfo("Check the results (failed to retrieve results)."
);
        handleResults(request, rs, skipResults, maxResults, callback);
      }

      // clear out remaining results
      while
 (ps.getMoreResults());

    } finally
 {
      try
 {
        closeResultSet(rs);
      } finally
 {
        closeStatement(ps);
      }
    }

  }

/**
   * Long form of the method to execute a query
   *
   * @param request - the request scope
   * @param conn - the database connection
   * @param sql - the SQL statement to execute
   * @param parameters - the parameters for the statement
   * @param skipResults - the number of results to skip
   * @param maxResults - the maximum number of results to return
   * @param callback - the row handler for the query
   *
   * @throws SQLException - if the query fails
   */
  public void executeQuery(RequestScope request, Connection conn, String sql, Object[] parameters,
                           int skipResults, int maxResults, RowHandlerCallback callback)
      throws SQLException {
    ErrorContext errorContext = request.getErrorContext();
    errorContext.setActivity("executing query");
    errorContext.setObjectId(sql);

    PreparedStatement ps = null;
    ResultSet rs = null;

    try {
      errorContext.setMoreInfo("Check the SQL Statement (preparation failed).");

      Integer rsType = request.getStatement().getResultSetType();
      if (rsType != null) {
        ps = conn.prepareStatement(sql, rsType.intValue(), ResultSet.CONCUR_READ_ONLY);
      } else {
        ps = conn.prepareStatement(sql);
      }

      Integer fetchSize = request.getStatement().getFetchSize();
      if (fetchSize != null) {
        ps.setFetchSize(fetchSize.intValue());
      }

      errorContext.setMoreInfo("Check the parameters (set parameters failed).");
      request.getParameterMap().setParameters(request, ps, parameters);

      errorContext.setMoreInfo("Check the statement (query failed).");

      ps.execute();
      rs = getFirstResultSet(ps);

      if (rs != null) {
        errorContext.setMoreInfo("Check the results (failed to retrieve results).");
        handleResults(request, rs, skipResults, maxResults, callback);
      }

      // clear out remaining results
      while (ps.getMoreResults());

    } finally {
      try {
        closeResultSet(rs);
      } finally {
        closeStatement(ps);
      }
    }

  }

 

其中handleResults(request, rs, skipResults, maxResults, callback)一句用于处理分页 ，其实此时查询已经执行完毕，可以不必关心handleResults方法，但为清楚起见，下面来看看 handleResults的实现：

private
 
void
 handleResults(RequestScope request, ResultSet rs, 
int
 skipResults, 
int
 maxResults, RowHandlerCallback callback) 
throws
 SQLException {
    try
 {
      request.setResultSet(rs);
      ResultMap resultMap = request.getResultMap();
      if
 (resultMap != 
null
) {
        // Skip Results
        if
 (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
          if
 (skipResults > 
0
) {
            rs.absolute(skipResults);
          }
        } else
 {
          for
 (
int
 i = 
0
; i < skipResults; i++) {
            if
 (!rs.next()) {
              break
;
            }
          }
        }

        // Get Results
        int
 resultsFetched = 
0
;
        while
 ((maxResults == SqlExecutor.NO_MAXIMUM_RESULTS || resultsFetched < maxResults) && rs.next()) {
          Object[] columnValues = resultMap.resolveSubMap(request, rs).getResults(request, rs);
          callback.handleResultObject(request, columnValues, rs);
          resultsFetched++;
        }
      }
    } finally
 {
      request.setResultSet(null
);
    }
  }

private void handleResults(RequestScope request, ResultSet rs, int skipResults, int maxResults, RowHandlerCallback callback) throws SQLException {
    try {
      request.setResultSet(rs);
      ResultMap resultMap = request.getResultMap();
      if (resultMap != null) {
        // Skip Results
        if (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
          if (skipResults > 0) {
            rs.absolute(skipResults);
          }
        } else {
          for (int i = 0; i < skipResults; i++) {
            if (!rs.next()) {
              break;
            }
          }
        }

        // Get Results
        int resultsFetched = 0;
        while ((maxResults == SqlExecutor.NO_MAXIMUM_RESULTS || resultsFetched < maxResults) && rs.next()) {
          Object[] columnValues = resultMap.resolveSubMap(request, rs).getResults(request, rs);
          callback.handleResultObject(request, columnValues, rs);
          resultsFetched++;
        }
      }
    } finally {
      request.setResultSet(null);
    }
  }

 

此处优先使用的是ResultSet的absolute方法定位记录，是否支持absolute取决于具体数据库驱动，但一般当前版本的数据库都支持该方法，如果不支持则逐条跳过前面的记录。由此可以看出如果数据库支持absolute，则ibatis 内置的分页 策略与特定数据库的物理分页 效率差距就在于物理分页 查询与不分页 查询在数据库中的执行效率的差距了。因为查询执行后读取数据前数据库并未把结果全部返回到内存，所以本身在存储占用上应该差距不大，如果都使用索引，估计执行速度也差不太多。

继续我们的话题。其实只要在executeQuery执行前组装sql，然后将其传给 executeQuery，并告诉handleResults我们不需要逻辑分页 即 可。拦截executeQuery可以采用aop动态实现，也可直接继承SqlExecutor覆盖executeQuery来静态地实现，相比之下后者 要简单许多，而且由于SqlExecutor没有实现任何接口，比较易变，动态拦截反到增加了维护的工作量，所以我们下面来覆盖 executeQuery：

package
 com.aladdin.dao.ibatis
.ext;

import
 java.sql.Connection;
import
 java.sql.SQLException;

import
 org.apache.commons.logging.Log;
import
 org.apache.commons.logging.LogFactory;

import
 com.aladdin.dao.dialect.Dialect;
import
 com.ibatis
.sqlmap.engine.execution.SqlExecutor;
import
 com.ibatis
.sqlmap.engine.mapping.statement.RowHandlerCallback;
import
 com.ibatis
.sqlmap.engine.scope.RequestScope;

public
 
class
 LimitSqlExecutor 
extends
 SqlExecutor {

    private
 
static
 
final
 Log logger = LogFactory.getLog(LimitSqlExecutor.
class
);

    private
 Dialect dialect;

    private
 
boolean
 enableLimit = 
true
;

    public
 Dialect getDialect() {
        return
 dialect;
    }

    public
 
void
 setDialect(Dialect dialect) {
        this
.dialect = dialect;
    }

    public
 
boolean
 isEnableLimit() {
        return
 enableLimit;
    }

    public
 
void
 setEnableLimit(
boolean
 enableLimit) {
        this
.enableLimit = enableLimit;
    }

    @Override
    public
 
void
 executeQuery(RequestScope request, Connection conn, String sql,
            Object[] parameters, int
 skipResults, 
int
 maxResults,
            RowHandlerCallback callback) throws
 SQLException {
        if
 ((skipResults != NO_SKIPPED_RESULTS || maxResults != NO_MAXIMUM_RESULTS)
                && supportsLimit()) {
            sql = dialect.getLimitString(sql, skipResults, maxResults);
            if
(logger.isDebugEnabled()){
                logger.debug(sql);
            }
            skipResults = NO_SKIPPED_RESULTS;
            maxResults = NO_MAXIMUM_RESULTS;
        }
        super
.executeQuery(request, conn, sql, parameters, skipResults,
                maxResults, callback);
    }

    public
 
boolean
 supportsLimit() {
        if
 (enableLimit && dialect != 
null
) {
            return
 dialect.supportsLimit();
        }
        return
 
false
;
    }

}

package com.aladdin.dao.ibatis
.ext;

import java.sql.Connection;
import java.sql.SQLException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.aladdin.dao.dialect.Dialect;
import com.ibatis
.sqlmap.engine.execution.SqlExecutor;
import com.ibatis
.sqlmap.engine.mapping.statement.RowHandlerCallback;
import com.ibatis
.sqlmap.engine.scope.RequestScope;

public class LimitSqlExecutor extends SqlExecutor {

    private static final Log logger = LogFactory.getLog(LimitSqlExecutor.class);
    
    private Dialect dialect;

    private boolean enableLimit = true;

    public Dialect getDialect() {
        return dialect;
    }

    public void setDialect(Dialect dialect) {
        this.dialect = dialect;
    }

    public boolean isEnableLimit() {
        return enableLimit;
    }

    public void setEnableLimit(boolean enableLimit) {
        this.enableLimit = enableLimit;
    }

    @Override
    public void executeQuery(RequestScope request, Connection conn, String sql,
            Object[] parameters, int skipResults, int maxResults,
            RowHandlerCallback callback) throws SQLException {
        if ((skipResults != NO_SKIPPED_RESULTS || maxResults != NO_MAXIMUM_RESULTS)
                && supportsLimit()) {
            sql = dialect.getLimitString(sql, skipResults, maxResults);
            if(logger.isDebugEnabled()){
                logger.debug(sql);
            }
            skipResults = NO_SKIPPED_RESULTS;
            maxResults = NO_MAXIMUM_RESULTS;            
        }
        super.executeQuery(request, conn, sql, parameters, skipResults,
                maxResults, callback);
    }

    public boolean supportsLimit() {
        if (enableLimit && dialect != null) {
            return dialect.supportsLimit();
        }
        return false;
    }

}

 其中：

skipResults = NO_SKIPPED_RESULTS;
maxResults = NO_MAXIMUM_RESULTS;

skipResults = NO_SKIPPED_RESULTS;
maxResults = NO_MAXIMUM_RESULTS;

 告诉handleResults不分页 （我们组装的sql已经使查询结果是分页 后的结果了），此处引入了类似hibenate中的数据库方言 接口Dialect，其代码如下：

package
 com.aladdin.dao.dialect;

public
 
interface
 Dialect {

    public
 
boolean
 supportsLimit();

    public
 String getLimitString(String sql, 
boolean
 hasOffset);

    public
 String getLimitString(String sql, 
int
 offset, 
int
 limit);
}

package com.aladdin.dao.dialect;

public interface Dialect {
    
    public boolean supportsLimit();

    public String getLimitString(String sql, boolean hasOffset);

    public String getLimitString(String sql, int offset, int limit);
}

 下面为Dialect接口的MySQL实现：

package
 com.aladdin.dao.dialect;

public
 
class
 MySQLDialect 
implements
 Dialect {

    protected
 
static
 
final
 String SQL_END_DELIMITER = 
";"
;

    public
 String getLimitString(String sql, 
boolean
 hasOffset) {
        return
 
new
 StringBuffer(sql.length() + 
20
).append(trim(sql)).append(
                hasOffset ? " limit ?,?"
 : 
" limit ?"
)
                .append(SQL_END_DELIMITER).toString();
    }

    public
 String getLimitString(String sql, 
int
 offset, 
int
 limit) {
        sql = trim(sql);
        StringBuffer sb = new
 StringBuffer(sql.length() + 
20
);
        sb.append(sql);
        if
 (offset > 
0
) {
            sb.append(" limit "
).append(offset).append(
','
).append(limit)
                    .append(SQL_END_DELIMITER);
        } else
 {
            sb.append(" limit "
).append(limit).append(SQL_END_DELIMITER);
        }
        return
 sb.toString();
    }

    public
 
boolean
 supportsLimit() {
        return
 
true
;
    }

    private
 String trim(String sql) {
        sql = sql.trim();
        if
 (sql.endsWith(SQL_END_DELIMITER)) {
            sql = sql.substring(0
, sql.length() - 
1
                    - SQL_END_DELIMITER.length());
        }
        return
 sql;
    }

}

package com.aladdin.dao.dialect;

public class MySQLDialect implements Dialect {

    protected static final String SQL_END_DELIMITER = ";";

    public String getLimitString(String sql, boolean hasOffset) {
        return new StringBuffer(sql.length() + 20).append(trim(sql)).append(
                hasOffset ? " limit ?,?" : " limit ?")
                .append(SQL_END_DELIMITER).toString();
    }

    public String getLimitString(String sql, int offset, int limit) {
        sql = trim(sql);
        StringBuffer sb = new StringBuffer(sql.length() + 20);
        sb.append(sql);
        if (offset > 0) {
            sb.append(" limit ").append(offset).append(',').append(limit)
                    .append(SQL_END_DELIMITER);
        } else {
            sb.append(" limit ").append(limit).append(SQL_END_DELIMITER);
        }
        return sb.toString();
    }

    public boolean supportsLimit() {
        return true;
    }

    private String trim(String sql) {
        sql = sql.trim();
        if (sql.endsWith(SQL_END_DELIMITER)) {
            sql = sql.substring(0, sql.length() - 1
                    - SQL_END_DELIMITER.length());
        }
        return sql;
    }

}

 接下来的工作就是把LimitSqlExecutor注入ibatis 中。我们是通过spring来使用ibatis 的，所以在我们的dao基类中执行注入，代码如下：

package
 com.aladdin.dao.ibatis
;

import
 java.io.Serializable;
import
 java.util.List;

import
 org.springframework.orm.ObjectRetrievalFailureException;
import
 org.springframework.orm.ibatis
.support.SqlMapClientDaoSupport;

import
 com.aladdin.dao.ibatis
.ext.LimitSqlExecutor;
import
 com.aladdin.domain.BaseObject;
import
 com.aladdin.util.ReflectUtil;
import
 com.ibatis
.sqlmap.client.SqlMapClient;
import
 com.ibatis
.sqlmap.engine.execution.SqlExecutor;
import
 com.ibatis
.sqlmap.engine.impl.ExtendedSqlMapClient;

public
 
abstract
 
class
 BaseDaoiBatis
 
extends
 SqlMapClientDaoSupport {

    private
 SqlExecutor sqlExecutor;

    public
 SqlExecutor getSqlExecutor() {
        return
 sqlExecutor;
    }

    public
 
void
 setSqlExecutor(SqlExecutor sqlExecutor) {
        this
.sqlExecutor = sqlExecutor;
    }

    public
 
void
 setEnableLimit(
boolean
 enableLimit) {
        if
 (sqlExecutor 
instanceof
 LimitSqlExecutor) {
            ((LimitSqlExecutor) sqlExecutor).setEnableLimit(enableLimit);
        }
    }

    public
 
void
 initialize() 
throws
 Exception {
        if
 (sqlExecutor != 
null
) {
            SqlMapClient sqlMapClient = getSqlMapClientTemplate()
                    .getSqlMapClient();
            if
 (sqlMapClient 
instanceof
 ExtendedSqlMapClient) {
                ReflectUtil.setFieldValue(((ExtendedSqlMapClient) sqlMapClient)
                        .getDelegate(), "sqlExecutor"
, SqlExecutor.
class
,
                        sqlExecutor);
            }
        }
    }

    ...

}

package com.aladdin.dao.ibatis
;

import java.io.Serializable;
import java.util.List;

import org.springframework.orm.ObjectRetrievalFailureException;
import org.springframework.orm.ibatis
.support.SqlMapClientDaoSupport;

import com.aladdin.dao.ibatis
.ext.LimitSqlExecutor;
import com.aladdin.domain.BaseObject;
import com.aladdin.util.ReflectUtil;
import com.ibatis
.sqlmap.client.SqlMapClient;
import com.ibatis
.sqlmap.engine.execution.SqlExecutor;
import com.ibatis
.sqlmap.engine.impl.ExtendedSqlMapClient;

public abstract class BaseDaoiBatis
 extends SqlMapClientDaoSupport {

    private SqlExecutor sqlExecutor;

    public SqlExecutor getSqlExecutor() {
        return sqlExecutor;
    }

    public void setSqlExecutor(SqlExecutor sqlExecutor) {
        this.sqlExecutor = sqlExecutor;
    }

    public void setEnableLimit(boolean enableLimit) {
        if (sqlExecutor instanceof LimitSqlExecutor) {
            ((LimitSqlExecutor) sqlExecutor).setEnableLimit(enableLimit);
        }
    }

    public void initialize() throws Exception {
        if (sqlExecutor != null) {
            SqlMapClient sqlMapClient = getSqlMapClientTemplate()
                    .getSqlMapClient();
            if (sqlMapClient instanceof ExtendedSqlMapClient) {
                ReflectUtil.setFieldValue(((ExtendedSqlMapClient) sqlMapClient)
                        .getDelegate(), "sqlExecutor", SqlExecutor.class,
                        sqlExecutor);
            }
        }
    }

    ...

}

 其中的initialize方法执行注入，稍后会看到此方法在spring Beans 配置中指定为init-method。由于sqlExecutor是 com.ibatis .sqlmap.engine.impl.ExtendedSqlMapClient的私有成员，且没有公开的set方法，所以此处通过反射绕过java的访问控制，下面是ReflectUtil的实现代码：

package
 com.aladdin.util;

import
 java.lang.reflect.Field;
import
 java.lang.reflect.Method;
import
 java.lang.reflect.Modifier;

import
 org.apache.commons.logging.Log;
import
 org.apache.commons.logging.LogFactory;

public
 
class
 ReflectUtil {

    private
 
static
 
final
 Log logger = LogFactory.getLog(ReflectUtil.
class
);

    public
 
static
 
void
 setFieldValue(Object target, String fname, Class ftype,
            Object fvalue) {
        if
 (target == 
null
                || fname == null
                || ""
.equals(fname)
                || (fvalue != null
 && !ftype.isAssignableFrom(fvalue.getClass()))) {
            return
;
        }
        Class clazz = target.getClass();
        try
 {
            Method method = clazz.getDeclaredMethod("set"
                    + Character.toUpperCase(fname.charAt(0
))
                    + fname.substring(1
), ftype);
            if
 (!Modifier.isPublic(method.getModifiers())) {
                method.setAccessible(true
);
            }
            method.invoke(target, fvalue);

        } catch
 (Exception me) {
            if
 (logger.isDebugEnabled()) {
                logger.debug(me);
            }
            try
 {
                Field field = clazz.getDeclaredField(fname);
                if
 (!Modifier.isPublic(field.getModifiers())) {
                    field.setAccessible(true
);
                }
                field.set(target, fvalue);
            } catch
 (Exception fe) {
                if
 (logger.isDebugEnabled()) {
                    logger.debug(fe);
                }
            }
        }
    }
}

package com.aladdin.util;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class ReflectUtil {

    private static final Log logger = LogFactory.getLog(ReflectUtil.class);

    public static void setFieldValue(Object target, String fname, Class ftype,
            Object fvalue) {
        if (target == null
                || fname == null
                || "".equals(fname)
                || (fvalue != null && !ftype.isAssignableFrom(fvalue.getClass()))) {
            return;
        }
        Class clazz = target.getClass();
        try {
            Method method = clazz.getDeclaredMethod("set"
                    + Character.toUpperCase(fname.charAt(0))
                    + fname.substring(1), ftype);
            if (!Modifier.isPublic(method.getModifiers())) {
                method.setAccessible(true);
            }
            method.invoke(target, fvalue);

        } catch (Exception me) {
            if (logger.isDebugEnabled()) {
                logger.debug(me);
            }
            try {
                Field field = clazz.getDeclaredField(fname);
                if (!Modifier.isPublic(field.getModifiers())) {
                    field.setAccessible(true);
                }
                field.set(target, fvalue);
            } catch (Exception fe) {
                if (logger.isDebugEnabled()) {
                    logger.debug(fe);
                }
            }
        }
    }
}

  到此剩下的就是通过Spring将sqlExecutor注入BaseDaoiBatis 中了，下面是Spring Beans配置文件：

<?
xml
 
version
=
"1.0"
 
encoding
=
"UTF-8"
?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
    "http://www.springframework.org/dtd/spring-beans.dtd">

<
beans
>
    <!-- Transaction manager for a single JDBC DataSource -->
    <
bean
 
id
=
"transactionManager"
 
class
=
"org.springframework.jdbc.datasource.DataSourceTransactionManager"
>
        <
property
 
name
=
"dataSource"
>
            <
ref
 
bean
=
"dataSource"
 
/>
        </
property
>
    </
bean
>

    <!-- SqlMap setup for iBATIS
 Database Layer -->
    <
bean
 
id
=
"sqlMapClient"
 
class
=
"org.springf