ClassFileStructure.java

package uk.kludje.experimental.property.reflect;

import uk.kludje.Ensure;

import java.io.*;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public final class ClassFileStructure implements DataWriter {

  private static final Log LOG = Log.logger(ClassFileStructure.class);

  public static final int MAGIC = 0xCAFEBABE;
  public static final short MINOR_VERSION = 0;
  public static final short MAJOR_VERSION = 52;

  private final List<ClassConstant> constants;
  private final byte[] remainder;

  ClassFileStructure(List<ClassConstant> constants, byte[] remainder) {
    this.constants = constants;
    this.remainder = remainder;
  }

  @Override
  public void writeTo(DataOutput output) throws IOException {
    output.writeInt(MAGIC);
    output.writeShort(MINOR_VERSION);
    output.writeShort(MAJOR_VERSION);
    output.writeShort(constants.size() + 1);
    for (ClassConstant constant : constants) {
      constant.writeTo(output);
    }
    output.write(remainder);
  }

  public String className() {
    throw new UnsupportedOperationException();
  }

  public byte[] toBytes() {
    throw new UnsupportedOperationException();
  }

  public static ClassFileStructure parse(DataInputStream input) throws IOException {
    Ensure.that(input != null, "input != null");
    Ensure.checked(input.readInt() == MAGIC, "magic == 0xCAFEBABE", IOException::new);
    Ensure.checked(input.readShort() == MINOR_VERSION, "minor == 0", IOException::new);
    Ensure.checked(input.readShort() == MAJOR_VERSION, "major == 52", IOException::new);

    int constPoolSize = input.readUnsignedShort();
    List<ClassConstant> constants = new ArrayList<>(constPoolSize);
    for (int i = 0; i < constPoolSize - 1; i++) {
      ClassConstant constant = ClassConstantParser.parse(input);
      constants.add(constant);

      LOG.debug("Constant %d: %s", i, constant);
    }

    ByteArrayOutputStream remainder = new ByteArrayOutputStream();
    byte[] buf = new byte[1024];
    int r;
    while ((r = input.read(buf)) > -1) {
      remainder.write(buf, 0, r);
    }

    return new ClassFileStructure(constants, remainder.toByteArray());
  }

  public static ClassFileStructure parse(URL url) throws IOException {
    try (InputStream in = url.openStream();
         DataInputStream data = new DataInputStream(in)) {
      return parse(data);
    }
  }
}