Question

mybatis怎么实现分页查询

Answer 1

Java代码
package page;

public interface Dialect {

public boolean supportsLimit();

public String getLimitString(String sql, boolean hasOffset);

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

public boolean supportsLimitOffset();
}

Java代码
package page;

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;
}

public boolean supportsLimitOffset() {
// TODO Auto-generated method stub
return true;
}

}

Java代码
package page;

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.MappedStatement.Builder;
import org.apache.ibatis.mapping.SqlSource;
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;

@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 = new BoundSql(ms.getConfiguration(), sql,
boundSql.getParameterMappings(),
boundSql.getParameterObject());
MappedStatement newMs = copyFromMappedStatement(ms,
new BoundSqlSqlSource(newBoundSql));
queryArgs[MAPPED_STATEMENT_INDEX] = newMs;
}
}

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());
builder.timeout(ms.getTimeout());
builder.parameterMap(ms.getParameterMap());
builder.resultMaps(ms.getResultMaps());
builder.cache(ms.getCache());
MappedStatement newMs = builder.build();
return newMs;
}

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

public void setProperties(Properties properties) {
String dialectClass = new PropertiesHelper(properties)
.getRequiredString("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;
}
}

}