效果：

一、自定义设置边距方法

SpaceItemDecoration.java

package com.custom.jfrb.ui.jfrb.finishedProduct; //自己包名位置

import android.graphics.Rect;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

/**
 * create by niuxi on 2023/9/26
 * 自定义类，GridLayoutManager设置边距
 */
public class SpaceItemDecoration extends RecyclerView.ItemDecoration {

    private int space; //边距值
    private int itemNum; //每行item数量

    public SpaceItemDecoration(int space,int itemNum) {
        this.space = space;
        this.itemNum = itemNum;
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        outRect.left = space;
        outRect.right = space;
        outRect.bottom = space;
        outRect.top = space;
        if (itemNum == 2){
            //一行两个时候，两个item靠近外面的那一边不设置边距
            if (parent.getChildLayoutPosition(view)%itemNum == 0){
                outRect.left = 0;
            }else if (parent.getChildLayoutPosition(view)%itemNum == 1){
                outRect.right = 0;
            }
        }
    }
}

二、Activity中调用设置边距

例子：给RecyclerView设置排列方式和边距

@InjectView(id = R.id.recyclerview_all_products)
private RecyclerView mRecyclerViewAllProducts;

private ProductAdapter adapter;

private List<FilePageBean> mList = new ArrayList<>();

重点看这里设置边距调用的方法：

//设置适配器（自定义）
adapter = new ProductAdapter();
mRecyclerViewAllProducts.setAdapter(adapter);

//设置布局方式
mRecyclerViewAllProducts.setLayoutManager(new GridLayoutManager(this,2));

//设置默认动画
mRecyclerViewAllProducts.setItemAnimator(new DefaultItemAnimator());

//设置边距值为10 item数量为2
mRecyclerView.addItemDecoration(new SpaceItemDecoration(10,2));
mRecyclerView.setPadding(0,0,0,0);

附：自定义的适配器
R.layout.list_item是单个Item的布局xml文件（可自定义）

class ProductAdapter extends RecyclerView.Adapter<MyViewHoder> {

        @NonNull
        @Override
        public MyViewHoder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = View.inflate(FinishedProductActivity.this, R.layout.list_item, null);
            return new MyViewHoder(view);
        }

        @Override
        public void onBindViewHolder(@NonNull FinishedProductActivity.MyViewHoder holder, int position) {
            FilePageBean item = mList.get(position);
            holder.mTvProductTitle.setText(item.getName());
            holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                   //Item点击监听
                }
            });
        }

        @Override
        public int getItemCount() {
            return mList.size();
        }

        public void refreshData(List<FilePageBean> list){
            mList.clear();
            mList.addAll(list);
            notifyDataSetChanged();
        }
    }

    static class MyViewHoder extends RecyclerView.ViewHolder {
        TextView mTvProductTitle;

        public MyViewHoder(@NonNull View itemView) {
            super(itemView);
            mTvProductTitle = itemView.findViewById(R.id.tv_product_title);
        }
    }

三、完成，Nice！