loadClass()
findLoadedClass(String)调用这个方法
protected Class<?> loadClass(String name, boolean resolve)
throws ClassNotFoundException
{
synchronized (getClassLoadingLock(name)) {
// 首先,查看这个Class是否已经被加载
Class<?> c = findLoadedClass(name);
//如果没有被加载,就查看父类加载器
if (c == null) {
long t0 = System.nanoTime();
try {
if (parent != null) {
//递归调用loadClass()
c = parent.loadClass(name, false);
} else {
//父类加载器是null,说明是启动类加载器,查找对应的Class
c = findBootstrapClassOrNull(name);
}
} catch (ClassNotFoundException e) {
// ClassNotFoundException thrown if class not found
// from the non-null parent class loader
}
//如果都没有找到
if (c == null) {
// If still not found, then invoke findClass in order
// to find the class.
//调用findClass()
long t1 = System.nanoTime();
c = findClass(name);
// this is the defining class loader; record the stats
sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
sun.misc.PerfCounter.getFindClasses().increment();
}
}
if (resolve) {
resolveClass(c);
}
return c;
}
}
findClass()
- 根据名称或位置加载.class字节码,然后使用defineClass
- 通常由子类去实现
protected Class<?> findClass(String name) throws ClassNotFoundException {
throw new ClassNotFoundException(name);
}
class NetworkClassLoader extends ClassLoader {
String host;
int port;
public Class findClass(String name) {
byte[] b = loadClassData(name);
return defineClass(name, b, 0, b.length);
}
private byte[] loadClassData(String name) {
// load the class data from the connection
}
}
definclass()
把字节码转化为Class
protected final Class<?> defineClass(String name, byte[] b, int off, int len)
throws ClassFormatError
{
return defineClass(name, b, off, len, null);
}