绘制国际象棋棋子时触发IllegalArgumentException：图片无法找到

异常信息 #

Exception in thread "main" java.lang.IllegalArgumentException: input == null!
at java.desktop/javax.imageio.ImageIO.read(ImageIO.java:1358)
at main.pieces.Piece.<init>(Piece.java:21)
at main.pieces.Knight.<init>(Knight.java:8)
at main.Board.addPieces(Board.java:23)
at main.Board.<init>(Board.java:19)
at main.App.main(App.java:14)

问题描述 #

尝试自定义棋盘绘制国际象棋棋子，但始终提示图片无法找到。已尝试移动res文件夹、确认文件为PNG格式，但问题依旧。

相关代码 #

App.java #

package main;
import javax.swing.*;
import java.awt.*;

public class App {
    public static void main(String[] args) throws Exception {
        
        JFrame frame = new JFrame();
        frame.getContentPane().setBackground(new Color(30, 30, 30));
        frame.setLayout(new GridBagLayout());
        frame.setMinimumSize(new Dimension(1000, 1000));
        frame.setLocationRelativeTo(null);

        Board board = new Board();
        frame.add(board);

        frame.setVisible(true);

    }
}

Board.java #

package main;
import main.pieces.Piece;
import main.pieces.Knight;
import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;

public class Board extends JPanel {

    public int tileSize = 85;

    int cols = 8;
    int rows = 8;

    ArrayList<Piece> pieceList = new ArrayList<>();

    public Board() {
        this.setPreferredSize(new Dimension(cols * tileSize, rows * tileSize));
        addPieces();
    }

    public void addPieces() {
        pieceList.add(new Knight(this, 2, 0, false));
    }

    public void paintComponent(Graphics g) {
        Graphics2D g2d = (Graphics2D) g;

        for (int r = 0; r < rows; r++) 
        for (int c = 0; c < cols; c++) {
            g2d.setColor((c + r) %2 == 0 ? new Color(230, 230, 230) : new Color(0, 0, 0));
            g2d.fillRect(c * tileSize, r * tileSize, tileSize, tileSize);
        }

        for (Piece piece : pieceList) {
            piece.paint(g2d);
        }
    }
}

Piece.java #

package main.pieces;

import main.Board;
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;

public class Piece {
    
    public int col, row;
    public int xPos, yPos; 

    public boolean isWhite;
    public String name;
    public int value;
    
    BufferedImage sheet;
    {
        try {
            sheet = ImageIO.read(ClassLoader.getSystemResourceAsStream("pieces.png"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    protected int sheetScale = sheet.getWidth() / 6;

    Image sprite;

    Board board;

    public Piece(Board board) {
        this.board = board;
    }

    public void paint(Graphics2D g2d) {

        g2d.drawImage(sprite, xPos, yPos, null);

    }

}

Knight.java #

package main.pieces;

import main.Board;
import java.awt.image.BufferedImage;

public class Knight extends Piece {
    public Knight(Board board, int col, int row, boolean isWhite) {
        super(board);
        this.col = col;
        this.row = row;
        this.xPos = col * board.tileSize;
        this.yPos = row * board.tileSize;


        this.isWhite = isWhite;
        this.name = "Knight";

        this.sprite = sheet.getSubimage(3 * sheetScale, isWhite ? 0 : sheetScale, sheetScale, sheetScale).getScaledInstance(sheetScale, sheetScale, BufferedImage.SCALE_SMOOTH);

    }
}

解决方法 #

1. 确认资源文件的正确位置 #

ClassLoader.getSystemResourceAsStream("pieces.png")会从类路径的根目录查找文件，所以要确保文件处于正确位置：

• 普通Java项目：将pieces.png直接放到src目录下，或者在IDE中把存放图片的文件夹标记为「资源目录」。
• Maven/Gradle项目：将图片放到src/main/resources目录下，编译后文件会自动进入类路径根目录。

2. 更换更可靠的资源加载方式 #

用当前类的ClassLoader加载资源，避免系统类加载器的路径问题，修改Piece类中的初始化块代码：

{
    try {
        // 用当前类的getResourceAsStream，/表示类路径根目录
        sheet = ImageIO.read(Piece.class.getResourceAsStream("/pieces.png"));
    } catch (IOException e) {
        e.printStackTrace();
    }
}

3. 检查文件有效性 #

• 确认文件名完全匹配（包括大小写，比如系统区分大小写时Pieces.png和pieces.png是不同文件）。
• 验证pieces.png是未损坏的有效PNG文件，可以用图片查看器打开确认。

4. 确认资源已被复制到编译目录 #

检查项目编译后的输出文件夹（比如bin或target/classes），确认pieces.png存在其中。如果不存在，需要在IDE中配置：将资源文件设置为编译时需要复制的文件。

内容的提问来源于stack exchange，提问作者Anthony McKinney