基于Java web服務器簡單實現(xiàn)一個Servlet容器
更新時間：2016年06月21日 15:06:00 作者：風一樣的碼農(nóng)
這篇文章主要為大家詳細介紹了基于Java web服務器簡單實現(xiàn)一個Servlet容器，感興趣的小伙伴們可以參考一下
上篇寫了一個簡單的Java web服務器實現(xiàn)，只能處理一些靜態(tài)資源的請求，本篇文章實現(xiàn)的Servlet容器基于前面的服務器做了個小改造，增加了Servlet請求的處理。
程序執(zhí)行步驟
1.創(chuàng)建一個ServerSocket對象；
2.調(diào)用ServerSocket對象的accept方法，等待連接，連接成功會返回一個Socket對象，否則一直阻塞等待；
3.從Socket對象中獲取InputStream和OutputStream字節(jié)流，這兩個流分別對應request請求和response響應；
4.處理請求：讀取InputStream字節(jié)流信息，轉成字符串形式，并解析，這里的解析比較簡單，僅僅獲取uri(統(tǒng)一資源標識符)信息;
5.處理響應（分兩種類型，靜態(tài)資源請求響應或servlet請求響應）：如果是靜態(tài)資源請求，則根據(jù)解析出來的uri信息，從WEB_ROOT目錄中尋找請求的資源資源文件, 讀取資源文件，并將其寫入到OutputStream字節(jié)流中；如果是Servlet請求，則首先生成一個URLClassLoader類加載器，加載請求的servlet類，創(chuàng)建servlet對象，執(zhí)行service方法（往OutputStream寫入響應的數(shù)據(jù)）；
6.關閉Socket對象；
7.轉到步驟2，繼續(xù)等待連接請求；
代碼實現(xiàn)：
添加依賴：
<!-- https://mvnrepository.com/artifact/javax.servlet/servlet-api --> <dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.3</version> </dependency>
服務器代碼：
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();
//等待連接請求
server.await();
}
public void await() {
ServerSocket serverSocket = null;
int port = 8080;
try {
//服務器套接字對象
serverSocket = new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
// 循環(huán)等待請求
while (true) {
Socket socket = null;
InputStream input = null;
OutputStream output = null;
try {
//等待連接，連接成功后，返回一個Socket對象
socket = serverSocket.accept();
input = socket.getInputStream();
output = socket.getOutputStream();
// 創(chuàng)建Request對象并解析
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;
}
// 創(chuàng)建 Response 對象
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(tài)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
* ...
* 該函數(shù)目的就是為了獲取/index.html字符串
*/
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信息，并從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文件寫入到OutputStream字節(jié)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(tài)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);
//類加載器，用于從指定JAR文件或目錄加載類
URLClassLoader loader = null;
try {
URLStreamHandler streamHandler = null;
//創(chuàng)建類加載器
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 {
//加載對應的servlet類
myClass = loader.loadClass(servletName);
} catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
Servlet servlet = null;
try {
//生產(chǎn)servlet實例
servlet = (Servlet) myClass.newInstance();
//執(zhí)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(tài)資源請求：
servlet請求（因為只是第一個字符串被刷新到瀏覽器，所以你不能看到第二個字符串Violets are blue。我們將在后續(xù)完善該容器）：
改進
前面實現(xiàn)的Servlet容器有一個嚴重的問題，用戶在servlet里可以直接將ServletRequest、ServletResponse向下轉 型為Request和Response類型，并直接調(diào)用其內(nèi)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，用戶只能訪問外觀類里定義的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);
// 類加載器，用于從指定JAR文件或目錄加載類
URLClassLoader loader = null;
try {
URLStreamHandler streamHandler = null;
// 創(chuàng)建類加載器
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 {
// 加載對應的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，防止用戶在servlet里直接將ServletRequest、ServletResponse向下轉型為Request和Response類型，
//并直接調(diào)用其內(nèi)部的public方法，因為RequestFacade、ResponseFacade里不會有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());
}
}
}
其它代碼與前面實現(xiàn)的Servlet容器基本一致。
驗證程序，分別請求靜態(tài)資源和Servlet，發(fā)現(xiàn)結果與前面實現(xiàn)的容器一致；
參考資料：《深入剖析Tomcat》
@author 風一樣的碼農(nóng)
以上就是本文的全部內(nèi)容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。
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