ClassFileloaderTest.java

package jvm.test;

import jvm.loader.ClassFileLoader;
import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;


public class ClassFileloaderTest {


    static String path1 = "/Users/john/Documents/mygit/coding2017/group24/315863321/target/classes/jvm";
    static String path2 = "/Users/john/Documents";


    @Before
    public void setUp() throws Exception {
    }

    @After
    public void tearDown() throws Exception {
    }

    @Test
    public void testClassPath() {

        ClassFileLoader loader = new ClassFileLoader();
        loader.addClassPath(path1);
        loader.addClassPath(path2);

        String clzPath = loader.getClassPath();

        Assert.assertEquals(path1 + ";" + path2, clzPath);

    }

    @Test
    public void testClassFileLength() {

        ClassFileLoader loader = new ClassFileLoader();
        loader.addClassPath(path1);

        String className = "EmployeeV1.class";

        byte[] byteCodes = loader.readBinaryCode(className);

        // 注意：这个字节数可能和你的JVM版本有关系， 你可以看看编译好的类到底有多大
        Assert.assertEquals(1026, byteCodes.length);

    }


    @Test
    public void testMagicNumber() {
        ClassFileLoader loader = new ClassFileLoader();
        loader.addClassPath(path1);
        String className = "EmployeeV1.class";
        byte[] byteCodes = loader.readBinaryCode(className);
        byte[] codes = new byte[]{byteCodes[0], byteCodes[1], byteCodes[2], byteCodes[3]};


        String acctualValue = this.byteToHexString(codes);

        Assert.assertEquals("cafebabe", acctualValue);
    }


    private String byteToHexString(byte[] codes) {
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < codes.length; i++) {
            byte b = codes[i];
            int value = b & 0xFF;
            String strHex = Integer.toHexString(value);
            if (strHex.length() < 2) {
                strHex = "0" + strHex;
            }
            buffer.append(strHex);
        }
        return buffer.toString();
    }

}