标签：插件 return int 简介 param boundSql sql Mybatis page
引言：
上面两节我们已经了解了Mybatis插件原理，下面是一个Mybatis分页的插件，可以为以后我们自定义开发插件做参考。
代码
/**
* Mybatis - 通用分页插件（如果开启二级缓存需要注意）
*/
@Intercepts({@Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class}),
@Signature(type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class})})
@Log4j
public class PageHelper implements Interceptor {
public static final ThreadLocal<Page> localPage = new ThreadLocal<Page>();
/**
* 开始分页
*
* @param pageNum
* @param pageSize
*/
public static void startPage(int pageNum, int pageSize) {
localPage.set(new Page(pageNum, pageSize));
}
/**
* 结束分页并返回结果，该方法必须被调用，否则localPage会一直保存下去，直到下一次startPage
*
* @return
*/
public static Page endPage() {
Page page = localPage.get();
localPage.remove();
return page;
}
public Object intercept(Invocation invocation) throws Throwable {
if (localPage.get() == null) {
return invocation.proceed();
}
if (invocation.getTarget() instanceof StatementHandler) {
StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
MetaObject metaStatementHandler = SystemMetaObject.forObject(statementHandler);
// 分离代理对象链(由于目标类可能被多个插件拦截，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 = SystemMetaObject.forObject(object);
}
// 分离最后一个代理对象的目标类
while (metaStatementHandler.hasGetter("target")) {
Object object = metaStatementHandler.getValue("target");
metaStatementHandler = SystemMetaObject.forObject(object);
}
MappedStatement mappedStatement = (MappedStatement) metaStatementHandler.getValue("delegate.mappedStatement");
//分页信息if (localPage.get() != null) {
Page page = localPage.get();
BoundSql boundSql = (BoundSql) metaStatementHandler.getValue("delegate.boundSql");
// 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);
//重写分页sql
metaStatementHandler.setValue("delegate.boundSql.sql", pageSql);
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插件
return invocation.proceed();
} else if (invocation.getTarget() instanceof ResultSetHandler) {
Object result = invocation.proceed();
Page page = localPage.get();
page.setResult((List) result);
return result;
}
return null;
}
/**
* 只拦截这两种类型的
* <br>StatementHandler
* <br>ResultSetHandler
*
* @param target
* @return
*/
public Object plugin(Object target) {
if (target instanceof StatementHandler || target instanceof ResultSetHandler) {
return Plugin.wrap(target, this);
} else {
return target;
}
}
public void setProperties(Properties properties) {
}
/**
* 修改原SQL为分页SQL
*
* @param sql
* @param page
* @return
*/
private String buildPageSql(String sql, Page page) {
StringBuilder pageSql = new StringBuilder(200);
pageSql.append("select * from (");
pageSql.append(sql);
pageSql.append(" ) temp limit ").append(page.getStartRow());
pageSql.append(" , ").append(page.getPageSize());
return pageSql.toString();
}
/**
* 获取总记录数
*
* @param sql
* @param connection
* @param mappedStatement
* @param boundSql
* @param page
*/
private void setPageParameter(String sql, Connection connection, MappedStatement mappedStatement,
BoundSql boundSql, Page page) {
// 记录总记录数
String countSql = "select count(0) from (" + sql + ") temp";
PreparedStatement countStmt = null;
ResultSet rs = null;
try {
countStmt = connection.prepareStatement(countSql);
BoundSql countBS = new BoundSql(mappedStatement.getConfiguration(), countSql,
boundSql.getParameterMappings(), boundSql.getParameterObject());
setParameters(countStmt, mappedStatement, countBS, boundSql.getParameterObject());
rs = countStmt.executeQuery();
int totalCount = 0;
if (rs.next()) {
totalCount = rs.getInt(1);
}
page.setTotal(totalCount);
int totalPage = totalCount / page.getPageSize() + ((totalCount % page.getPageSize() == 0) ? 0 : 1);
page.setPages(totalPage);
} catch (SQLException e) {
log.error("Ignore this exception", e);
} finally {
try {
rs.close();
} catch (SQLException e) {
log.error("Ignore this exception", e);
}
try {
countStmt.close();
} catch (SQLException e) {
log.error("Ignore this exception", e);
}
}
}
/**
* 代入参数值
*
* @param ps
* @param mappedStatement
* @param boundSql
* @param parameterObject
* @throws SQLException
*/
private void setParameters(PreparedStatement ps, MappedStatement mappedStatement, BoundSql boundSql,
Object parameterObject) throws SQLException {
ParameterHandler parameterHandler = new DefaultParameterHandler(mappedStatement, parameterObject, boundSql);
parameterHandler.setParameters(ps);
}
@Data //采用lombok插件编译
public static class Page<E> {
private int pageNum;
private int pageSize;
private int startRow;
private int endRow;
private long total;
private int pages;
private List<E> result;
public Page(int pageNum, int pageSize) {
this.pageNum = pageNum;
this.pageSize = pageSize;
this.startRow = pageNum > 0 ? (pageNum - 1) * pageSize : 0;
this.endRow = pageNum * pageSize;
}
}
}
标签：插件,return,int,简介,param,boundSql,sql,Mybatis,page 来源： https://blog.csdn.net/weixin_44046437/article/details/100526967
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