boundSqlInterceptors初始化拦截链参数问题咨询

[lingaoju]

• 我已在 issues 搜索类似问题，并且不存在相同的问题.

使用环境

• PageHelper 版本: 5.2.0
• 数据库类型和版本: mysql8.0

功能建议

PageInterceptor中配置boundSqlInterceptors参数，设置自定义的BoundSqlInterceptor，进行拦截，修改前置修改SQL然后在进行分页，但是这个配置只会进行一次调用，debug发现是调用完这个链之后不会初始化 index,如下图

详细说明，尽可能提供(伪)代码示例。

期望的结果：

期望按理来说每次sql都应该走一遍这个拦截器链，现在用boundSqlInterceptors配置的默认的拦截器链不会重新进入该链方法

[lingaoju]

@OverRide
public BoundSql doBoundSql(BoundSqlInterceptor.Type type, BoundSql boundSql, CacheKey cacheKey) {
if (this.interceptors == null || this.interceptors.size() == this.index) {
return this.original != null ? this.original.doBoundSql(type, boundSql, cacheKey) : boundSql;
} else {
return this.interceptors.get(this.index++).boundSql(type, boundSql, cacheKey, this);
}
}
图片不知道是否上传成功，这边用代码解释以下，这个是BoundSqlInterceptorChain类部分代码， 这里的this.index++调用后在代码中没有重置，导致不会在进入这个拦截链

[a83313886]

我也发现这个问题了。原因在于BoundSqlInterceptorChain的index字段使用，而PageHelper调用时直接复用了同一个实例，一方面在多线程场景下存在并发问题，另一方面就如 @lingaoju 所说的-计数器没有重置。

PageHelper使用同一个实例的代码如下：

    @Override
    public BoundSql doBoundSql(BoundSqlInterceptor.Type type, BoundSql boundSql, CacheKey cacheKey) {
           // ...
            BoundSqlInterceptor.Chain defaultChain = pageBoundSqlInterceptors != null ? pageBoundSqlInterceptors.getChain() : null;
            if (boundSqlInterceptor != null) {
                chain = new BoundSqlInterceptorChain(defaultChain, Arrays.asList(boundSqlInterceptor));
            } else if (defaultChain != null) {
                chain = defaultChain;
            }
            // ...
        return chain.doBoundSql(type, boundSql, cacheKey);
    }

[abel533]

这是个BUG，现在的修改方式是把chain当成了模板，执行的时候初始化一个实例来解决这个问题，大家可以看看代码，测试看看有没有问题：

package com.github.pagehelper;

import org.apache.ibatis.cache.CacheKey;
import org.apache.ibatis.mapping.BoundSql;

import java.util.List;

public class BoundSqlInterceptorChain implements BoundSqlInterceptor.Chain {
    private final BoundSqlInterceptor.Chain original;
    private final List<BoundSqlInterceptor> interceptors;

    private int     index = 0;
    private boolean executable;

    public BoundSqlInterceptorChain(BoundSqlInterceptor.Chain original, List<BoundSqlInterceptor> interceptors) {
        this(original, interceptors, false);
    }

    private BoundSqlInterceptorChain(BoundSqlInterceptor.Chain original, List<BoundSqlInterceptor> interceptors, boolean executable) {
        this.original = original;
        this.interceptors = interceptors;
        this.executable = executable;
    }

    @Override
    public BoundSql doBoundSql(BoundSqlInterceptor.Type type, BoundSql boundSql, CacheKey cacheKey) {
        if(executable) {
            return _doBoundSql(type, boundSql, cacheKey);
        } else {
            return new BoundSqlInterceptorChain(original, interceptors, true).doBoundSql(type, boundSql, cacheKey);
        }
    }

    private BoundSql _doBoundSql(BoundSqlInterceptor.Type type, BoundSql boundSql, CacheKey cacheKey) {
        if (this.interceptors == null || this.interceptors.size() == this.index) {
            return this.original != null ? this.original.doBoundSql(type, boundSql, cacheKey) : boundSql;
        } else {
            return this.interceptors.get(this.index++).boundSql(type, boundSql, cacheKey, this);
        }
    }

}