app1
(建议读者在看本章之前,先看how tomcat works 读书笔记(一)----------一个简单的web服务器
回顾我们上一章,我们开发了一个最最简单的web服务器,它可以使用户访问服务器内的静态资源。当然这是远远不够的,在这一节里,我们就试着让服务器在能相应静态资源的基础上继续支持servlet。
servlet接口
javax.servlet.Servlet接口定义了五个方法,如下:
我们所使用的servlet都是Servlet接口的间接实现类。
每当我们实例化一个servlet的时候,servlet容器都会先唯一的调用一次init()方法进行初始化,然后再调用service()方法来处理用户的需求,最后在销毁servlet前容器会调用destroy()方法。
我们看看,这一节我们要用的测试servlet。
import javax.servlet.*;
import com.jspsmart.upload.Request;
import java.io.IOException;
import java.io.PrintWriter;
public class PrimitiveServlet implements Servlet {
public void init(ServletConfig config) throws ServletException {
System.out.println("init");
}
public void service(ServletRequest request, ServletResponse response)
throws ServletException, IOException {
System.out.println("from service");
PrintWriter out = response.getWriter();
out.println("Hello. Roses are red.");
out.print("Violets are blue.");
// out.flush();
}
public void destroy() {
System.out.println("destroy");
}
public String getServletInfo() {
return null;
}
public ServletConfig getServletConfig() {
return null;
}
}
Servlet定义的5个方法,它都实现了(不过我们这一节要实现的servlet还没有能力自动调用init和destroy方法)。
再看看我们的主方法,程序就从这里开始(和上一节的HttpServer差别不是很大)
package ex02.pyrmont;
import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetAddress;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
public class HttpServer1 {
/** WEB_ROOT is the directory where our HTML and other files reside.
* For this package, WEB_ROOT is the "webroot" directory under the working
* directory.
* The working directory is the location in the file system
* from where the java command was invoked.
*/
// shutdown command
private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";
// the shutdown command received
private boolean shutdown = false;
public static void main(String[] args) {
HttpServer1 server = new HttpServer1();
server.await();
}
public void await() {
ServerSocket serverSocket = null;
int port = 8080;
try {
serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
}
catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
// Loop waiting for a request
while (!shutdown) {
Socket socket = null;
InputStream input = null;
OutputStream output = null;
try {
socket = serverSocket.accept();
input = socket.getInputStream();
output = socket.getOutputStream();
// create Request object and parse
Request request = new Request(input);
request.parse();
// create Response object
Response response = new Response(output);
response.setRequest(request); //没有再这里直接处理静态资源
//而是判断到底请求的事静态资源还是servlet
// check if this is a request for a servlet or a static resource
// a request for a servlet begins with "/servlet/"
if (request.getUri().startsWith("/servlet/")) {
ServletProcessor1 processor = new ServletProcessor1();
processor.process(request, response);
}
else {
StaticResourceProcessor processor = new StaticResourceProcessor();
processor.process(request, response);
}
// Close the socket
socket.close();
//check if the previous URI is a shutdown command
shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
}
catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
}
}
大家可以很清楚地看到,这部分和上一节的不同主要就在response部分,更准确的说就是在这
if (request.getUri().startsWith("/servlet/")) {
ServletProcessor1 processor = new ServletProcessor1();
processor.process(request, response);
}
else {
StaticResourceProcessor processor = new StaticResourceProcessor();
processor.process(request, response);
}
我们看看,如果请求是以servlet开头的该如何处理。
package ex02.pyrmont;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLStreamHandler;
import java.io.File;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class ServletProcessor1 {
public void process(Request request, Response response) {
String uri = request.getUri();
String servletName = uri.substring(uri.lastIndexOf("/") + 1);
URLClassLoader loader = null;
try {
// create a URLClassLoader //try部分的主要功能就是产生一个URLClassLoader
URL[] urls = new URL[1];
URLStreamHandler streamHandler = null;
File classPath = new File(Constants.WEB_ROOT);
//下面的URL构造函数为
//java.net.URL.URL(String protocol, String host, String file) throws MalformedURLException
String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;
System.out.println(servletName+"*****"+Constants.WEB_ROOT+" "+repository);
//下面的URL构造函数为
//java.net.URL.URL(URL context, String spec, URLStreamHandler handler) throws MalformedURLException
//至于 URLStreamHandler是什么东西 暂时不必理会
urls[0] = new URL(null, repository, streamHandler);
loader = new URLClassLoader(urls);
}
catch (IOException e) {
System.out.println(e.toString() );
}
Class<?> myClass = null;
try {
myClass = loader.loadClass(servletName); //加载请求的servlet
}
catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
Servlet servlet = null;
try {
servlet = (Servlet) myClass.newInstance(); //生成实例 并调用service方法
servlet.service((ServletRequest) request, (ServletResponse) response);
}
catch (Exception e) {
System.out.println(e.toString());
}
catch (Throwable e) {
System.out.println(e.toString());
}
}
}
看看另一部分,如果请求的不是servlet(这一节就是静态资源)该如何处理
package ex02.pyrmont;
import java.io.IOException;
public class StaticResourceProcessor {
public void process(Request request, Response response) {
try {
response.sendStaticResource();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
跟第一节没有什么区别。
我们的request类要实现ServletRequest接口
package ex02.pyrmont;
import java.io.InputStream;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;
import javax.servlet.AsyncContext;
import javax.servlet.DispatcherType;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class Request implements ServletRequest {
private InputStream input;
private String uri;
public Request(InputStream input) {
this.input = input;
}
public String getUri() {
return uri;
}
private String parseUri(String requestString) {
int index1, index2;
index1 = requestString.indexOf(' ');
if (index1 != -1) {
index2 = requestString.indexOf(' ', index1 + 1);
if (index2 > index1)
return requestString.substring(index1 + 1, index2);
}
return null;
}
public void parse() {
// Read a set of characters from the socket
StringBuffer request = new StringBuffer(2048);
int i;
byte[] buffer = new byte[2048];
try {
i = input.read(buffer);
}
catch (IOException e) {
e.printStackTrace();
i = -1;
}
for (int j=0; j<i; j++) {
request.append((char) buffer[j]);
}
System.out.print(request.toString());
uri = parseUri(request.toString());
}
public void removeAttribute(String attribute) {
}
public void setAttribute(String key, Object value) {
}
public void setCharacterEncoding(String encoding)
throws UnsupportedEncodingException {
}
//缺少的方法 用Eclipse自动生成即可 不再赘述
}
同样的response也要实现ServletResponse接口
package ex02.pyrmont;
import java.io.OutputStream;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.File;
import java.io.PrintWriter;
import java.util.Locale;
import javax.servlet.ServletResponse;
import javax.servlet.ServletOutputStream;
import com.sun.org.apache.bcel.internal.generic.NEW;
public class Response implements ServletResponse {
private static final int BUFFER_SIZE = 1024;
Request request;
OutputStream output;
PrintWriter writer;
public Response(OutputStream output) {
this.output = output;
}
public void setRequest(Request request) {
this.request = request;
}
/* This method is used to serve a static page */
public void sendStaticResource() throws IOException {
byte[] bytes = new byte[BUFFER_SIZE];
FileInputStream fis = null;
try {
/* request.getUri has been replaced by request.getRequestURI */
System.out.println(Constants.WEB_ROOT+" ***** "+ request.getUri());
File file = new File(Constants.WEB_ROOT, request.getUri());
fis = new FileInputStream(file);
/*
HTTP Response = Status-Line
*(( general-header | response-header | entity-header ) CRLF)
CRLF
[ message-body ]
Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
*/
int ch = fis.read(bytes, 0, BUFFER_SIZE);
System.out.println("response **");
while (ch!=-1) {
output.write(bytes, 0, ch);
ch = fis.read(bytes, 0, BUFFER_SIZE);
}
}
catch (FileNotFoundException e) {
String errorMessage = "HTTP/1.1 404 File Not Found\r\n" +
"Content-Type: text/html\r\n" +
"Content-Length: 23\r\n" +
"\r\n" +
"<h1>File Not Found</h1>";
output.write(errorMessage.getBytes());
}
finally {
if (fis!=null)
fis.close();
}
}
public PrintWriter getWriter() throws IOException {
// autoflush is true, println() will flush,
// but print() will not.
writer = new PrintWriter(output, true);
return writer;
}
//一样 部分代码 直接让Eclipse 自动生成即可
}
试验一下
http://localhost:8080/servlet/PrimitiveServlet
控制台显示
GET /servlet/PrimitiveServlet HTTP/1.1
Accept: image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash,
Accept-Language: zh-cn
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; SV1)
Accept-Encoding: gzip, deflate
Host: localhost:8080
Connection: Keep-Alive
PrimitiveServlet*****D:\Java Code\UpLoad\webroot file:D:\Java Code\UpLoad\webroot\
from service
大家仔细看看
Violets are blue. 这句话没有打印出来
大家看看Response类getWriter方法里的PrintWriter一行
上面的英文,我就不解释了
这个bug在以后的版本中会修改
app2
上面的代码其实还存在一个问题
在request部分中parseUri是private的,在这一节中这样其实是可以的,但问题是这个方法有可能在外部类中使用,应该是public的。
如果改成public,问题又出现了
public void service(ServletRequest request, ServletResponse response)
throws ServletException, IOException {
System.out.println("from service");
Request r=(Request) request;
System.out.println(r.parseUri("sdf"));
PrintWriter out = response.getWriter();
out.println("Hello. Roses are red.");
out.print("Violets are blue.");
out.flush();
}
我把servlet类中的service改成上面的样子,大家看看,其实request的parseUri方法在servlet里是不应该被使用的!
那怎么办?
第一种,将parseUri方法的public方法改成默认的访问修饰符,包外的类就不能访问了。
不过还有另一种方式
门面模式!!
在上面的例子中,我们写的request实现了ServletRequest,我们可以再写一个类RequestFacade类让他也实现ServletRequest(response 类似)
package ex02.pyrmont;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.UnsupportedEncodingException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
public class RequestFacade implements ServletRequest {
private ServletRequest request = null;
public RequestFacade(Request request) {
this.request = request;
}
public String getRemoteHost() {
return request.getRemoteHost();
}
//省略对ServletRequest接口的实现
//servletrequest接口的方法 在RequestFacade 内部实现时 都调用类的属性request来实现
public void setCharacterEncoding(String encoding)
throws UnsupportedEncodingException {
request.setCharacterEncoding(encoding);
}
}
再看看 ServletProcessor 改成如下
Servlet servlet = null;
RequestFacade requestFacade = new RequestFacade(request);
ResponseFacade responseFacade = new ResponseFacade(response);
try {
servlet = (Servlet) myClass.newInstance();
servlet.service((ServletRequest) requestFacade, (ServletResponse) responseFacade);
}
catch (Exception e) {
System.out.println(e.toString());
}
catch (Throwable e) {
System.out.println(e.toString());
}
httpServer 也改成如下
if (request.getUri().startsWith("/servlet/")) {
ServletProcessor2 processor = new ServletProcessor2();
processor.process(requestFacade , responseFacade );
}
app1给servlet里面传递的参数实际上是Request类型的,有调用parseUri方法的危险。
app2给servlet里面传递的参数实际上是RequestFacade,它根本就没有parseUri方法,自然就安全了。
这篇文章中 对书中的源码有删减 大家可以下载完整版本的
深入剖析tomcat 源码
http://down.51cto.com/data/486495
