基於Java web伺服器簡單實現一個Servlet容器

基於Java web伺服器簡單實現一個Servlet容器
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上篇寫了一個簡單的Java web伺服器實現,只能處理一些靜態資源的請求,本篇文章實現的Servlet容器基於前面的伺服器做了個小改造,增加了Servlet請求的處理。

 程式執行步驟
 1.建立一個ServerSocket物件;
 2.呼叫ServerSocket物件的accept方法,等待連線,連線成功會返回一個Socket物件,否則一直阻塞等待;
 3.從Socket物件中獲取InputStream和OutputStream位元組流,這兩個流分別對應request請求和response響應;
 4.處理請求:讀取InputStream位元組流資訊,轉成字串形式,並解析,這裡的解析比較簡單,僅僅獲取uri(統一資源識別符號)資訊;
 5.處理響應(分兩種型別,靜態資源請求響應或servlet請求響應):如果是靜態資源請求,則根據解析出來的uri資訊,從WEB_ROOT目錄中尋找請求的資源資原始檔, 讀取資原始檔,並將其寫入到OutputStream位元組流中;如果是Servlet請求,則首先生成一個URLClassLoader類載入器,載入請求的servlet類,建立servlet物件,執行service方法(往OutputStream寫入響應的資料);
 6.關閉Socket物件;
 7.轉到步驟2,繼續等待連線請求; 

程式碼實現:
 新增依賴: 


<!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.3</version>
</dependency>

伺服器程式碼: 


package ex02.pyrmont.first;
import java.net.Socket;
import java.net.ServerSocket;
import java.net.InetAddress;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
import ex02.pyrmont.Request;
import ex02.pyrmont.Response;
import ex02.pyrmont.StaticResourceProcessor;
public class HttpServer1 {
// 關閉服務命令
private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";
public static void main(String[] args) {
HttpServer1 server = new HttpServer1();
//等待連線請求
server.await();
}
public void await() {
ServerSocket serverSocket = null;
int port = 8080;
try {
//伺服器套接字物件
serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
// 迴圈等待請求
while (true) {
Socket socket = null;
InputStream input = null;
OutputStream output = null;
try {
//等待連線,連線成功後,返回一個Socket物件
socket = serverSocket.accept();
input = socket.getInputStream();
output = socket.getOutputStream();
// 建立Request物件並解析
Request request = new Request(input);
request.parse();
// 檢查是否是關閉服務命令
if (request.getUri().equals(SHUTDOWN_COMMAND)) {
break;
}
// 建立 Response 物件
Response response = new Response(output);
response.setRequest(request);
if (request.getUri().startsWith("/servlet/")) {
//請求uri以/servlet/開頭,表示servlet請求
ServletProcessor1 processor = new ServletProcessor1();
processor.process(request, response);
} else {
//靜態資源請求
StaticResourceProcessor processor = new StaticResourceProcessor();
processor.process(request, response);
}
// 關閉 socket
socket.close();
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
}
}

常量類: 


package ex02.pyrmont;
import java.io.File;
public class Constants {
public static final String WEB_ROOT = System.getProperty("user.dir")
File.separator   "webroot";
public static final String WEB_SERVLET_ROOT = System.getProperty("user.dir")
File.separator   "target"   File.separator   "classes";
}

Request: 


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.RequestDispatcher;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletRequest;
public class Request implements ServletRequest {
private InputStream input;
private String uri;
public Request(InputStream input) {
this.input = input;
}
public String getUri() {
return uri;
}
/**
* 
* requestString形式如下:
* GET /index.html HTTP/1.1
* Host: localhost:8080
* Connection: keep-alive
* Cache-Control: max-age=0
* ...
* 該函式目的就是為了獲取/index.html字串
*/
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;
}
//從InputStream中讀取request資訊,並從request中獲取uri值
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());
}
/* implementation of the ServletRequest */
public Object getAttribute(String attribute) {
return null;
}
public Enumeration<?> getAttributeNames() {
return null;
}
public String getRealPath(String path) {
return null;
}
public RequestDispatcher getRequestDispatcher(String path) {
return null;
}
public boolean isSecure() {
return false;
}
public String getCharacterEncoding() {
return null;
}
public int getContentLength() {
return 0;
}
public String getContentType() {
return null;
}
public ServletInputStream getInputStream() throws IOException {
return null;
}
public Locale getLocale() {
return null;
}
public Enumeration<?> getLocales() {
return null;
}
public String getParameter(String name) {
return null;
}
public Map<?, ?> getParameterMap() {
return null;
}
public Enumeration<?> getParameterNames() {
return null;
}
public String[] getParameterValues(String parameter) {
return null;
}
public String getProtocol() {
return null;
}
public BufferedReader getReader() throws IOException {
return null;
}
public String getRemoteAddr() {
return null;
}
public String getRemoteHost() {
return null;
}
public String getScheme() {
return null;
}
public String getServerName() {
return null;
}
public int getServerPort() {
return 0;
}
public void removeAttribute(String attribute) {
}
public void setAttribute(String key, Object value) {
}
public void setCharacterEncoding(String encoding)
throws UnsupportedEncodingException {
}
}

Response: 


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;
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;
}
//將web檔案寫入到OutputStream位元組流中
public void sendStaticResource() throws IOException {
byte[] bytes = new byte[BUFFER_SIZE];
FileInputStream fis = null;
try {
/* request.getUri has been replaced by request.getRequestURI */
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);
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();
}
}
/** implementation of ServletResponse */
public void flushBuffer() throws IOException {
}
public int getBufferSize() {
return 0;
}
public String getCharacterEncoding() {
return null;
}
public Locale getLocale() {
return null;
}
public ServletOutputStream getOutputStream() throws IOException {
return null;
}
public PrintWriter getWriter() throws IOException {
// autoflush is true, println() will flush,
// but print() will not.
writer = new PrintWriter(output, true);
return writer;
}
public boolean isCommitted() {
return false;
}
public void reset() {
}
public void resetBuffer() {
}
public void setBufferSize(int size) {
}
public void setContentLength(int length) {
}
public void setContentType(String type) {
}
public void setLocale(Locale locale) {
}
}

靜態資源請求處理: 


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();
}
}
}

Servlet請求處理: 


package ex02.pyrmont.first;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLStreamHandler;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import ex02.pyrmont.Constants;
import ex02.pyrmont.Request;
import ex02.pyrmont.Response;
public class ServletProcessor1 {
public void process(Request request, Response response) {
String uri = request.getUri();
String servletName = uri.substring(uri.lastIndexOf("/")   1);
//類載入器,用於從指定JAR檔案或目錄載入類
URLClassLoader loader = null;
try {
URLStreamHandler streamHandler = null;
//建立類載入器
loader = new URLClassLoader(new URL[]{new URL(null, "file:"   Constants.WEB_SERVLET_ROOT, streamHandler)});
} catch (IOException e) {
System.out.println(e.toString());
}
Class<?> myClass = null;
try {
//載入對應的servlet類
myClass = loader.loadClass(servletName);
} catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
Servlet servlet = null;
try {
//生產servlet例項
servlet = (Servlet) myClass.newInstance();
//執行ervlet的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());
}
}
}

Servlet類: 


import javax.servlet.*;
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.");
}
public void destroy() {
System.out.println("destroy");
}
public String getServletInfo() {
return null;
}
public ServletConfig getServletConfig() {
return null;
}
}

結果測試:
 靜態資源請求:

 

servlet請求(因為只是第一個字串被重新整理到瀏覽器,所以你不能看到第二個字串Violets are blue。我們將在後續完善該容器):

 

改進 

前面實現的Servlet容器有一個嚴重的問題,使用者在servlet裡可以直接將ServletRequest、ServletResponse向下轉 型為Request和Response型別,並直接呼叫其內部的public方法,這是一個不好的設計,改進方法是給Request、Response 增加外觀類,這樣,使用者只能訪問外觀類裡定義的public方法。
 Request外觀類 


package ex02.pyrmont.second;
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;
import ex02.pyrmont.Request;
public class RequestFacade implements ServletRequest {
private ServletRequest request = null;
public RequestFacade(Request request) {
this.request = request;
}
/* implementation of the ServletRequest */
public Object getAttribute(String attribute) {
return request.getAttribute(attribute);
}
public Enumeration<?> getAttributeNames() {
return request.getAttributeNames();
}
@SuppressWarnings("deprecation")
public String getRealPath(String path) {
return request.getRealPath(path);
}
public RequestDispatcher getRequestDispatcher(String path) {
return request.getRequestDispatcher(path);
}
public boolean isSecure() {
return request.isSecure();
}
public String getCharacterEncoding() {
return request.getCharacterEncoding();
}
public int getContentLength() {
return request.getContentLength();
}
public String getContentType() {
return request.getContentType();
}
public ServletInputStream getInputStream() throws IOException {
return request.getInputStream();
}
public Locale getLocale() {
return request.getLocale();
}
public Enumeration<?> getLocales() {
return request.getLocales();
}
public String getParameter(String name) {
return request.getParameter(name);
}
public Map<?, ?> getParameterMap() {
return request.getParameterMap();
}
public Enumeration<?> getParameterNames() {
return request.getParameterNames();
}
public String[] getParameterValues(String parameter) {
return request.getParameterValues(parameter);
}
public String getProtocol() {
return request.getProtocol();
}
public BufferedReader getReader() throws IOException {
return request.getReader();
}
public String getRemoteAddr() {
return request.getRemoteAddr();
}
public String getRemoteHost() {
return request.getRemoteHost();
}
public String getScheme() {
return request.getScheme();
}
public String getServerName() {
return request.getServerName();
}
public int getServerPort() {
return request.getServerPort();
}
public void removeAttribute(String attribute) {
request.removeAttribute(attribute);
}
public void setAttribute(String key, Object value) {
request.setAttribute(key, value);
}
public void setCharacterEncoding(String encoding)
throws UnsupportedEncodingException {
request.setCharacterEncoding(encoding);
}
}

Response外觀類


package ex02.pyrmont.second;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Locale;
import javax.servlet.ServletResponse;
import javax.servlet.ServletOutputStream;
import ex02.pyrmont.Response;
public class ResponseFacade implements ServletResponse {
private ServletResponse response;
public ResponseFacade(Response response) {
this.response = response;
}
public void flushBuffer() throws IOException {
response.flushBuffer();
}
public int getBufferSize() {
return response.getBufferSize();
}
public String getCharacterEncoding() {
return response.getCharacterEncoding();
}
public Locale getLocale() {
return response.getLocale();
}
public ServletOutputStream getOutputStream() throws IOException {
return response.getOutputStream();
}
public PrintWriter getWriter() throws IOException {
return response.getWriter();
}
public boolean isCommitted() {
return response.isCommitted();
}
public void reset() {
response.reset();
}
public void resetBuffer() {
response.resetBuffer();
}
public void setBufferSize(int size) {
response.setBufferSize(size);
}
public void setContentLength(int length) {
response.setContentLength(length);
}
public void setContentType(String type) {
response.setContentType(type);
}
public void setLocale(Locale locale) {
response.setLocale(locale);
}
}

處理Servlet請求類: 


package ex02.pyrmont.second;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLStreamHandler;
import java.io.IOException;
import javax.servlet.Servlet;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import ex02.pyrmont.Constants;
import ex02.pyrmont.Request;
import ex02.pyrmont.Response;
public class ServletProcessor2 {
public void process(Request request, Response response) {
String uri = request.getUri();
String servletName = uri.substring(uri.lastIndexOf("/")   1);
// 類載入器,用於從指定JAR檔案或目錄載入類
URLClassLoader loader = null;
try {
URLStreamHandler streamHandler = null;
// 建立類載入器
loader = new URLClassLoader(new URL[] { new URL(null, "file:"
Constants.WEB_SERVLET_ROOT, streamHandler) });
} catch (IOException e) {
System.out.println(e.toString());
}
Class<?> myClass = null;
try {
// 載入對應的servlet類
myClass = loader.loadClass(servletName);
} catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
Servlet servlet = null;
//給request、response增加外觀類,安全性考慮,防止使用者在servlet裡直接將ServletRequest、ServletResponse向下轉型為Request和Response型別,
//並直接呼叫其內部的public方法,因為RequestFacade、ResponseFacade裡不會有parse、sendStaticResource等方法;
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());
}
}
}

其它程式碼與前面實現的Servlet容器基本一致。
 驗證程式,分別請求靜態資源和Servlet,發現結果與前面實現的容器一致;

 參考資料:《深入剖析Tomcat》

@author   風一樣的碼農

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