OffsetLimitInterceptor.java

package cn.org.rapid_framework.mybatis.plugin;



import java.util.Properties;

import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.ParameterMapping;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.mapping.MappedStatement.Builder;
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 cn.org.rapid_framework.jdbc.dialect.Dialect;
import cn.org.rapid_framework.util.PropertiesHelper;

/**
 * 为ibatis3提供基于方言(Dialect)的分页查询的插件
 * 
 * 将拦截Executor.query()方法实现分页方言的插入.
 * 
 * 配置文件内容:
 * <pre>
 * 	<plugins>
 *		<plugin interceptor="cn.org.rapid_framework.ibatis3.plugin.OffsetLimitInterceptor">
 *			<property name="dialectClass" value="cn.org.rapid_framework.jdbc.dialect.MySQLDialect"/>
 *		</plugin>
 *	</plugins>
 * </pre>
 * 
 * @author badqiu
 *
 */

@Intercepts({@Signature(
		type= Executor.class,
		method = "query",
		args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class OffsetLimitInterceptor implements Interceptor{
	static int MAPPED_STATEMENT_INDEX = 0;
	static int PARAMETER_INDEX = 1;
	static int ROWBOUNDS_INDEX = 2;
	static int RESULT_HANDLER_INDEX = 3;
	
	Dialect dialect;
	
	public Object intercept(Invocation invocation) throws Throwable {
		processIntercept(invocation.getArgs());
		return invocation.proceed();
	}

	void processIntercept(final Object[] queryArgs) {
		//queryArgs = query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler)
		MappedStatement ms = (MappedStatement)queryArgs[MAPPED_STATEMENT_INDEX];
		Object parameter = queryArgs[PARAMETER_INDEX];
		final RowBounds rowBounds = (RowBounds)queryArgs[ROWBOUNDS_INDEX];
		int offset = rowBounds.getOffset();
		int limit = rowBounds.getLimit();
		
		if(dialect.supportsLimit() && (offset != RowBounds.NO_ROW_OFFSET || limit != RowBounds.NO_ROW_LIMIT)) {
			BoundSql boundSql = ms.getBoundSql(parameter);
			String sql = boundSql.getSql().trim();
			if (dialect.supportsLimitOffset()) {
				sql = dialect.getLimitString(sql, offset, limit);
				offset = RowBounds.NO_ROW_OFFSET;
			} else {
				sql = dialect.getLimitString(sql, 0, limit);
			}
			limit = RowBounds.NO_ROW_LIMIT;
			
			queryArgs[ROWBOUNDS_INDEX] = new RowBounds(offset,limit);
			
			BoundSql newBoundSql = copyFromBoundSql(ms, boundSql, sql);
			
			MappedStatement newMs = copyFromMappedStatement(ms, new BoundSqlSqlSource(newBoundSql));
			queryArgs[MAPPED_STATEMENT_INDEX] = newMs;
		}
	}

	private BoundSql copyFromBoundSql(MappedStatement ms, BoundSql boundSql,
			String sql) {
		BoundSql newBoundSql = new BoundSql(ms.getConfiguration(),sql, boundSql.getParameterMappings(), boundSql.getParameterObject());
		for (ParameterMapping mapping : boundSql.getParameterMappings()) {
		    String prop = mapping.getProperty();
		    if (boundSql.hasAdditionalParameter(prop)) {
		        newBoundSql.setAdditionalParameter(prop, boundSql.getAdditionalParameter(prop));
		    }
		}
		return newBoundSql;
	}
	
	//see: MapperBuilderAssistant
	private MappedStatement copyFromMappedStatement(MappedStatement ms,SqlSource newSqlSource) {
		Builder builder = new MappedStatement.Builder(ms.getConfiguration(),ms.getId(),newSqlSource,ms.getSqlCommandType());
		
		builder.resource(ms.getResource());
		builder.fetchSize(ms.getFetchSize());
		builder.statementType(ms.getStatementType());
		builder.keyGenerator(ms.getKeyGenerator());
		builder.keyProperty(ms.getKeyProperty());
		
		//setStatementTimeout()
		builder.timeout(ms.getTimeout());
		
		//setStatementResultMap()
		builder.parameterMap(ms.getParameterMap());
		
		//setStatementResultMap()
		builder.resultMaps(ms.getResultMaps());
		builder.resultSetType(ms.getResultSetType());
	    
		//setStatementCache()
		builder.cache(ms.getCache());
		builder.flushCacheRequired(ms.isFlushCacheRequired());
		builder.useCache(ms.isUseCache());
		
		return builder.build();
	}

	public Object plugin(Object target) {
		return Plugin.wrap(target, this);
	}

	public void setProperties(Properties properties) {
		String dialectClass = new PropertiesHelper(properties).getRequiredProperty("dialectClass");
		try {
			dialect = (Dialect)Class.forName(dialectClass).newInstance();
		} catch (Exception e) {
			throw new RuntimeException("cannot create dialect instance by dialectClass:"+dialectClass,e);
		} 
		System.out.println(OffsetLimitInterceptor.class.getSimpleName()+".dialect="+dialectClass);
	}
	
	public static class BoundSqlSqlSource implements SqlSource {
		BoundSql boundSql;
		public BoundSqlSqlSource(BoundSql boundSql) {
			this.boundSql = boundSql;
		}
		public BoundSql getBoundSql(Object parameterObject) {
			return boundSql;
		}
	}
	
}