很可能是因为来自DataInputStream的弃用方法readLine()。正如其注释中所述

此方法无法将字节正确转换为字符。从JDK 1.1开始，读取文本行的首选方法是通过BufferedReader.readLine()方法。使用DataInputStream类读取行的程序可以通过替换表单的代码转换为使用BufferedReader类：

DataInputStream d = new DataInputStream(in);

有：

BufferedReader d

= new BufferedReader(new InputStreamReader(in));

当我根据这个建议改变你的程序时，它对我有用(我做了一些其他的改动：

(更新为处理PGM的P2和P5口味)

public static void main(String args[]) throws Exception {

try {

InputStream f = ClassLoader.getSystemClassLoader().getResourceAsStream("lena.pgm");

BufferedReader d = new BufferedReader(new InputStreamReader(f));

String magic = d.readLine(); // first line contains P2 or P5

String line = d.readLine(); // second line contains height and width

while (line.startsWith("#")) {

line = d.readLine();

}

Scanner s = new Scanner(line);

int width = s.nextInt();

int height = s.nextInt();

line = d.readLine();// third line contains maxVal

s = new Scanner(line);

int maxVal = s.nextInt();

byte[][] im = new byte[height][width];

int count = 0;

int b = 0;

try {

while (count < height*width) {

b = d.read() ;

if ( b < 0 )

break ;

if (b == '\n') { // do nothing if new line encountered

}

// else if (b == '#') {

// d.readLine();

// }

// else if (Character.isWhitespace(b)) { // do nothing if whitespace encountered

// }

else {

if ( "P5".equals(magic) ) { // Binary format

im[count / width][count % width] = (byte)((b >> 8) & 0xFF);

count++;

im[count / width][count % width] = (byte)(b & 0xFF);

count++;

}

else { // ASCII format

im[count / width][count % width] = (byte)b ;

count++;

}

}

}

} catch (EOFException eof) {

eof.printStackTrace(System.out) ;

}

System.out.println("Height=" + height);

System.out.println("Width=" + height);

System.out.println("Required elements=" + (height * width));

System.out.println("Obtained elements=" + count);

}

catch(Throwable t) {

t.printStackTrace(System.err) ;

return ;

}

}