java - 为什么重启程序后DataFlavors变了？

Question

我写了这个方法

public static void printFlavors() {
    Clipboard systemClipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
    Transferable transferData = systemClipboard.getContents(null);
    for (DataFlavor dataFlavor : transferData.getTransferDataFlavors()) {
        System.out.println(dataFlavor);
    }
}

使用 Java，我将一个字符串写入剪贴板，然后调用 printFlavors() 并获取

java.awt.datatransfer.DataFlavor[mimetype=application/x-java-serialized-object;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=unicode]

当我第一次停止程序然后运行一个调用 printFlavors() 的新程序时，我得到了一个完全不同的结果:

java.awt.datatransfer.DataFlavor[mimetype=application/x-java-text-encoding;representationclass=[B]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.Reader]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.Reader]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.Reader]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.CharBuffer]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.CharBuffer]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.CharBuffer]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[C]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[C]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[C]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.io.InputStream;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=java.nio.ByteBuffer;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/html;representationclass=[B;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=application/x-java-serialized-object;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.Reader]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.lang.String]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.CharBuffer]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[C]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=unicode]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=UTF-16]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=UTF-8]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=UTF-16BE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=UTF-16LE]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=ISO-8859-1]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=windows-1252]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.io.InputStream;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=java.nio.ByteBuffer;charset=US-ASCII]
java.awt.datatransfer.DataFlavor[mimetype=text/plain;representationclass=[B;charset=US-ASCII]

为什么结果会变？

Answer 1

我假设您使用类似以下内容将内容添加到剪贴板:

systemClipboard.setContents(new StringSelection("abc"), null);

然后，当您读取可用的数据类型时，我假设剪贴板能够准确地确定剪贴板内容的类型(它仍然引用它的 StringSelection)并且它确切地知道它是什么类型的内容(编码等)。

如果您在以编程方式设置剪贴板内容后暂停程序的执行(通过线程 hibernate 或调试断点)，然后在程序之外更改剪贴板内容(例如通过复制一些文本)，您应该获得与重新启动应用程序相同的输出(更多数据风格有助于将内容转换为 Java 表示)，因为内容来自外部世界(操作系统)。

我过去曾使用过一些 java Clipboard，这些是我的假设；与往常一样，如果您真的需要确切地知道发生了什么，最好检查源代码。

编辑

我查看了源代码，我的假设是正确的 - 当应用程序将 StringSelection 存储到剪贴板时，它会一直引用它，直到剪贴板内容更改并仅返回 StringSelection 支持的数据类型:

private static final DataFlavor[] flavors = {
   DataFlavor.stringFlavor,
   DataFlavor.plainTextFlavor // deprecated
};