It seems that every StructureComponent generates before its location is visited.

Now I want to make a mod that generates a StructureComponent in explored area.

Example : Steve places a "Desert Temple Sapling" in visited ocean and lets it grow a desert temple.

I have tried buildComponent, but nothing was generated.

The search engines only gave me unrelated information, like how to add a new village house type.

How to make such "Desert Temple Sapling" works?

I think you need StructureStart#generateStructure. It's called when the structure is starting to be generated.

I think you need StructureStart#generateStructure. It's called when the structure is starting to be generated.

Now some components can be generated.

The basic code looks like this:

public class _SS extends StructureStart{
public _SS(World xw,Random xr,int xx,int xy,int xz){
	StructureComponent yy=new ComponentScatteredFeaturePieces.DesertPyramid(xr,xx,xz);
	components.add(yy);
	boundingBox=new StructureBoundingBox(xx-80,0,xz-80,xx+80,255,xz+80);
	yy.buildComponent(yy, components, xr);
	generateStructure(xw, xr, boundingBox);
	updateBoundingBox();
}
}

Using

 new _SS(xw,xr,xx,xy,xz);

can create a Desert Temple without the underground chest room.

However, we need to do advanced researching for how to correctly create the full structure for indivisual structures.