不会 java ，闲的用 rust 写了一个。

```rust
use std::{
error::Error,
fs::File,
io::{Read, Write},
};
fn main() {
run().unwrap();
}
fn run() -> Result<(), Box<dyn Error>> {
let mut out = File::create("out.jpg")?;
let mut files = [
File::open("files/p1")?,
File::open("files/p2")?,
File::open("files/p3")?,
];
let mut buffer = vec![0; 255];
let log = std::fs::read_to_string("files/splitlog.txt")?;
for (l, r) in log.lines().map(|line| {
let mut s = line.split('\t');
let l: usize = s.next().unwrap().parse().unwrap();
let r: usize = s.next().unwrap().parse().unwrap();
(l, r)
}) {
let file = &mut files[l];
let buffer = &mut buffer[..r];
file.read_exact(buffer)?;
out.write_all(buffer)?;
}

Ok(())
}
```