ClassFileLoaderTest.java

package com.coding2017.week4.jvm.loader;

import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import static org.junit.Assert.*;

/**
 * Created by kaitao.li on 2017/4/3.
 */
public class ClassFileLoaderTest {

    static String path1 = "/Users/kaitao.li/code/study/coding2017/group01/280646174/basic/target/classes";
    static String path2 = "C:\\temp";

    @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 = "com.coding2017.week4.jvm.test.EmployeeV1";

        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(1068, byteCodes.length);

    }

    @Test
    public void testMagicNumber() {
        ClassFileLoader loader = new ClassFileLoader();
        loader.addClassPath(path1);
        String className = "com.coding2017.week4.jvm.test.EmployeeV1";
        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();
    }

}