tomcat 7 中的类加载器学习

tomcat 7自带很多junit测试用例，可以帮助我们窥探源码的秘密。以下使用来测试类加载器的一个测试用例。类加载器也是对象，他们用来将类从类从。class文件加载到虚拟机，这些已经讲了很多，深入jvm中说的很详细，什么双亲委派模型，在书中还以tomcat为例讲解。

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package org.apache.catalina.loader;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.junit.Assert;
import org.junit.Test;
import org.apache.catalina.core.StandardContext;
import org.apache.catalina.startup.Tomcat;
import org.apache.catalina.startup.TomcatBaseTest;
import org.apache.tomcat.util.buf.ByteChunk;

public class TestWebappClassLoader extends TomcatBaseTest {

@Test
public void testGetURLs() throws Exception {

File f = new File("test/webresources/war-url-connection.war");

String[] expected = new String[2];
String warUrl = f.toURI().toURL().toExternalForm();
expected[0] = "jar:" + warUrl + "!/WEB-INF/classes/";
expected[1] = "jar:" + warUrl + "!/WEB-INF/lib/test.jar";

Tomcat tomcat = getTomcatInstance();
// Must have a real docBase - just use temp
StandardContext ctx =
(StandardContext)tomcat.addContext("", f.getAbsolutePath());

tomcat.start();

//获得当前的类加载器
ClassLoader cl = ctx.getLoader().getClassLoader();

Assert.assertTrue(cl instanceof URLClassLoader);
//获得类加载器中对应的路径

try (URLClassLoader ucl = (URLClassLoader) cl) {
URL[] urls = ucl.getURLs();
Assert.assertEquals(expected.length, urls.length);
String[] actual = new String[urls.length];
for (int i = 0; i < urls.length; i++) {
actual[i] = urls[i].toExternalForm();
System.out.println(actual[i]);
}
Assert.assertArrayEquals(expected, actual);
//获得类加载器的各级父类加载器
while(cl!=null)
{
System.out.println(cl);
cl=cl.getParent();

}


}
}
@Test
public void testBug53454() throws Exception {
Tomcat tomcat = getTomcatInstance();

// Must have a real docBase - just use temp
StandardContext ctx = (StandardContext)
tomcat.addContext("", System.getProperty("java.io.tmpdir"));
System.out.println("临时目录"+System.getProperty("java.io.tmdir"));

// Map the test Servlet
MyServlet largeBodyServlet = new MyServlet();
Tomcat.addServlet(ctx, "MyServlet", largeBodyServlet);
ctx.addServletMapping("/", "MyServlet");

tomcat.start();

Map<String,List<String>> resHeaders= new HashMap<>();
int rc = headUrl("http://localhost:" + getPort() + "/", new ByteChunk(),
resHeaders);

Assert.assertEquals(HttpServletResponse.SC_OK, rc);
ClassLoader cl=ctx.getClass().getClassLoader();
while(cl!=null)
{
System.out.println(cl);
cl=cl.getParent();
}


}
private static class MyServlet extends HttpServlet {

private static final long serialVersionUID = 1L;

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {


}

}
}

输出结果：

临时目录null

sun.misc.Launcher$AppClassLoader@4bb8d481
sun.misc.Launcher$ExtClassLoader@538787fd

jar:file:/F:/javal/Tomcat-Research-trunk/test/webresources/war-url-connection.war!/WEB-INF/classes/
jar:file:/F:/javal/Tomcat-Research-trunk/test/webresources/war-url-connection.war!/WEB-INF/lib/test.jar
WebappClassLoader
  context: 
  delegate: false
----------> Parent Classloader:
sun.misc.Launcher$AppClassLoader@4bb8d481

sun.misc.Launcher$AppClassLoader@4bb8d481
sun.misc.Launcher$ExtClassLoader@538787fd
一月 26, 2015 6:52:56 下午 org.apache.coyote.AbstractProtocol stop
INFO: Stopping ProtocolHandler ["http-nio-127.0.0.1-auto-2-64075"]
一月 26, 2015 6:52:56 下午 org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-nio-127.0.0.1-auto-2-64075"]

如果使用临时目录和默认目录，应用的类加载器是AppClassLoader,而其的目录可以每个应用的类加载器为WebappClassLoader