如何讀取.class文件的完全限定名稱

Question

嘿，我認為標題總結了它，但仍然。

我需要從已編譯的.class文件中提取 對象的完全限定名稱 ，有人能指出我正確的方向嗎？

謝謝，
亞當。

Answer 1

getClass().getName()

更新：您可以將類文件加載到byte[] （使用標准i / o），然后使用getClass().getClassLoader().defineClass(...)

Answer 2

public String getFullClassName(String classFileName) throws IOException {           
        File file = new File(classFileName);

        FileChannel roChannel = new RandomAccessFile(file, "r").getChannel(); 
        ByteBuffer bb = roChannel.map(FileChannel.MapMode.READ_ONLY, 0, (int)roChannel.size());         

        Class<?> clazz = defineClass((String)null, bb, (ProtectionDomain)null);
        return clazz.getName();
    }

Answer 3

使用像BCEL這樣的庫將類文件讀入內存並查詢它的類名。

Answer 4

您可以通過解析二進制文件來閱讀它。 類文件格式在VM Spec中定義。

如果您不熟悉解析二進制文件，請查看DataInputStream。

Answer 5

根據您使用的IDE，可能有一種機制來執行此操作。 例如，在eclipse中，您可以深入查看.class文件並右鍵單擊它並選擇“復制完全限定名稱”。

舊版本的eclipse可能沒有此功能，但我之前使用過這個插件：

http://www.jave.de/eclipse/copyfully/index.html

它的工作原理大致相同。 希望這可以幫助。

Answer 6

您可以在JSF實現的AnnotationScanner中查看示例，他們會手動加載類（以避免perm-space污染）來查找JSF注釋。 特別看看這個：

   /**
     * This class is encapsulating binary .class file information as defined at
     * http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html
     * <p/>
     * This is used by the annotation frameworks to quickly scan .class files
     * for the presence of annotations. This avoid the annotation framework
     * having to load each .class file in the class loader.
     * <p/>
     * Taken from the GlassFish V2 source base.
     */
    @SuppressWarnings({"UnusedDeclaration"})
    private static final class ClassFile {

        private static final int magic = 0xCAFEBABE;

        public static final int ACC_PUBLIC = 0x1;
        public static final int ACC_PRIVATE = 0x2;
        public static final int ACC_PROTECTED = 0x4;
        public static final int ACC_STATIC = 0x8;
        public static final int ACC_FINAL = 0x10;
        public static final int ACC_SYNCHRONIZED = 0x20;
        public static final int ACC_THREADSAFE = 0x40;
        public static final int ACC_TRANSIENT = 0x80;
        public static final int ACC_NATIVE = 0x100;
        public static final int ACC_INTERFACE = 0x200;
        public static final int ACC_ABSTRACT = 0x400;

        public short majorVersion;
        public short minorVersion;
        public ConstantPoolInfo constantPool[];
        public short accessFlags;
        public ConstantPoolInfo thisClass;
        public ConstantPoolInfo superClass;
        public ConstantPoolInfo interfaces[];

        /**
         * bunch of stuff I really don't care too much for now.
         * <p/>
         * FieldInfo           fields[]; MethodInfo          methods[];
         * AttributeInfo       attributes[];
         */

        ByteBuffer header;
        ConstantPoolInfo constantPoolInfo = new ConstantPoolInfo();

        // ------------------------------------------------------------ Constructors


        /**
         * Creates a new instance of ClassFile
         */
        public ClassFile() {
            header = ByteBuffer.allocate(12000);
        }

        // ---------------------------------------------------------- Public Methods


        public void setConstantPoolInfo(ConstantPoolInfo poolInfo) {
            constantPoolInfo = poolInfo;
        }


        /**
         * Read the input channel and initialize instance data structure.
         *
         * @param in a <code>ReadableByteChannel</code> that provides the bytes
         *  of the classfile
         *
         * @return <code>true</code> if the bytes representing this classfile include
         *  one of the annotations we're looking for.
         *
         * @throws IOException if an I/O error occurs while reading the class
         */
        public boolean containsAnnotation(ReadableByteChannel in)
              throws IOException {

            /**
             * this is the .class file layout
             *
             ClassFile {
             u4 magic;
             u2 minor_version;
             u2 major_version;
             u2 constant_pool_count;
             cp_info constant_pool[constant_pool_count-1];
             u2 access_flags;
             u2 this_class;
             u2 super_class;
             u2 interfaces_count;
             u2 interfaces[interfaces_count];
             u2 fields_count;
             field_info fields[fields_count];
             u2 methods_count;
             method_info methods[methods_count];
             u2 attributes_count;
             attribute_info attributes[attributes_count];
             }
             **/
            header.clear();
            long read = (long) in.read(header);
            if (read == -1) {
                return false;
            }
            header.rewind();

            if (header.getInt() != magic) {
                return false;
            }

            minorVersion = header.getShort();
            majorVersion = header.getShort();
            int constantPoolSize = header.getShort();

            return constantPoolInfo
                  .containsAnnotation(constantPoolSize, header, in);

        }

    } // END ClassFile