public StringBuilder buildPageSqlForMysql(String sql, PageParameter page) {
StringBuilder pageSql = new StringBuilder(100);
pageSql.append(sql);
pageSql.append(" limit " + page.getOffset() + "," + page.getLimit());
return pageSql;
}
@Override
public Object intercept(Invocation invocation) throws Throwable {
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
MetaObject metaStatementHandler =
MetaObject.forObject(
statementHandler,
DEFAULT_OBJECT_FACTORY,
DEFAULT_OBJECT_WRAPPER_FACTORY,
DEFAULT_REFLECTOR_FACTORY);
// 分离代理对象链(由于目标类可能被多个拦截器拦截，从而形成多次代理，通过下面的两次循环
// 可以分离出最原始的的目标类)
while (metaStatementHandler.hasGetter("h")) {
Object object = metaStatementHandler.getValue("h");
metaStatementHandler =
MetaObject.forObject(
object,
DEFAULT_OBJECT_FACTORY,
DEFAULT_OBJECT_WRAPPER_FACTORY,
DEFAULT_REFLECTOR_FACTORY);
}
// 分离最后一个代理对象的目标类
while (metaStatementHandler.hasGetter("target")) {
Object object = metaStatementHandler.getValue("target");
metaStatementHandler =
MetaObject.forObject(
object,
DEFAULT_OBJECT_FACTORY,
DEFAULT_OBJECT_WRAPPER_FACTORY,
DEFAULT_REFLECTOR_FACTORY);
}
if (null == dialect || "".equals(dialect)) {
logger.warn("Property dialect is not setted,use default 'mysql' ");
dialect = defaultDialect;
}
if (null == pageSqlId || "".equals(pageSqlId)) {
logger.warn("Property pageSqlId is not setted,use default '.*Page$' ");
pageSqlId = defaultPageSqlId;
}
MappedStatement mappedStatement =
(MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
PageParameter page = null;
Object type = metaStatementHandler.getValue("delegate.boundSql.parameterObject");
if (PageParameter.class.isInstance(type)) {
page = (PageParameter) type;
}
// 只重写需要分页的sql语句。通过MappedStatement的ID匹配，默认重写以Page结尾的
// MappedStatement的sql
if (mappedStatement.getId().matches(pageSqlId) && page != null && page.getLimit() > 0) {
BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");
Object parameterObject = boundSql.getParameterObject();
if (parameterObject == null) {
throw new NullPointerException("parameterObject is null!");
} else {
// 分页参数作为参数对象parameterObject的一个属性
String sql = boundSql.getSql();
// 重写sql
String pageSql = buildPageSql(sql, page, dialect);
metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);
// 采用物理分页后，就不需要mybatis的内存分页了，所以重置下面的两个参数
metaStatementHandler.setValue("delegate.rowBounds.offset", RowBounds.NO_ROW_OFFSET);
metaStatementHandler.setValue("delegate.rowBounds.limit", RowBounds.NO_ROW_LIMIT);
Connection connection = (Connection) invocation.getArgs()[0];
// 重设分页参数里的总页数等
setPageParameter(sql, connection, mappedStatement, boundSql, page);
}
}
// 将执行权交给下一个拦截器
return invocation.proceed();
}