servlet genericservlet httpservlet

概述：

servlet执行的流程是：创建对象-》初始化-》处理用户请求-》销毁。只有用户第一次访问servlet时候，如果web server中没有该servlet的对象那么才创建，并且初始化只执行一次，servlet全部是单例，销毁在服务器关闭的时候进行执行。

Servlet接口：

//接口源代码
public abstract interface Servlet
{
public abstract void init(ServletConfig paramServletConfig)
throws ServletException;
public abstract ServletConfig getServletConfig();
public abstract void service(ServletRequest paramServletRequest, ServletResponse paramServletResponse)
throws ServletException, IOException;
public abstract String getServletInfo();
public abstract void destroy();
}

GenericServlet抽象类：

该类是一个通用的servlet类，实现Servlet和ServletCofig接口，字它的子类都必须实现service()方法。

//源代码
package javax.servlet;
import java.io.IOException;
import java.io.Serializable;
import java.util.Enumeration;
import java.util.ResourceBundle;
public abstract class GenericServlet
implements Servlet, ServletConfig, Serializable
{
private static final String LSTRING_FILE = "javax.servlet.LocalStrings";
private static ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.LocalStrings");
private transient ServletConfig config;
public void destroy()
{
}
public String getInitParameter(String name)
{
ServletConfig sc = getServletConfig();
if (sc == null) {
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getInitParameter(name);//调用ServletConfig对象的同名的方法
}
public Enumeration getInitParameterNames()
{
ServletConfig sc = getServletConfig();
if (sc == null) {
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getInitParameterNames();//调用ServletConfig对象的同名的方法
}
public ServletConfig getServletConfig()
{
return this.config;
}
public ServletContext getServletContext()
{
ServletConfig sc = getServletConfig();
if (sc == null) {
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getServletContext();//调用ServletConfig对象的同名的方法
}
public String getServletInfo()
{
return "";
}
public void init(ServletConfig config)
throws ServletException
{
this.config = config;//产行ServletConfig对象
init();
}
public void init()
throws ServletException
{
}
public void log(String msg)
{
getServletContext().log(getServletName() + ": " + msg);
}
public void log(String message, Throwable t)
{
getServletContext().log(getServletName() + ": " + message, t);
}
public abstract void service(ServletRequest paramServletRequest, ServletResponse paramServletResponse)
throws ServletException, IOException;//抽象方法，执行网络请求
public String getServletName()
{
ServletConfig sc = getServletConfig();
if (sc == null) {
throw new IllegalStateException(lStrings.getString("err.servlet_config_not_initialized"));
}
return sc.getServletName();
}
}

HttpServlet抽象类：

扩展了GenericSerlvet，需要重写doGet,doPost方法。

//源代码
package javax.servlet.http;
import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public abstract class HttpServlet extends GenericServlet
implements Serializable
{
private static final String METHOD_DELETE = "DELETE";
private static final String METHOD_HEAD = "HEAD";
private static final String METHOD_GET = "GET";
private static final String METHOD_OPTIONS = "OPTIONS";
private static final String METHOD_POST = "POST";
private static final String METHOD_PUT = "PUT";
private static final String METHOD_TRACE = "TRACE";
private static final String HEADER_IFMODSINCE = "If-Modified-Since";
private static final String HEADER_LASTMOD = "Last-Modified";
private static final String LSTRING_FILE = "javax.servlet.http.LocalStrings";
private static ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_get_not_supported");
if (protocol.endsWith("1.1"))
resp.sendError(405, msg);
else
resp.sendError(400, msg);
}
protected long getLastModified(HttpServletRequest req)
{
return -1L;
}
protected void doHead(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
NoBodyResponse response = new NoBodyResponse(resp);
doGet(req, response);
response.setContentLength();
}
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_post_not_supported");
if (protocol.endsWith("1.1"))
resp.sendError(405, msg);
else
resp.sendError(400, msg);
}
protected void doPut(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_put_not_supported");
if (protocol.endsWith("1.1"))
resp.sendError(405, msg);
else
resp.sendError(400, msg);
}
protected void doDelete(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String protocol = req.getProtocol();
String msg = lStrings.getString("http.method_delete_not_supported");
if (protocol.endsWith("1.1"))
resp.sendError(405, msg);
else
resp.sendError(400, msg);
}
private Method[] getAllDeclaredMethods(Class c)
{
if (c.equals(HttpServlet.class)) {
return null;
}
Method[] parentMethods = getAllDeclaredMethods(c.getSuperclass());
Method[] thisMethods = c.getDeclaredMethods();
if ((parentMethods != null) && (parentMethods.length > 0)) {
Method[] allMethods = new Method[parentMethods.length + thisMethods.length];
System.arraycopy(parentMethods, 0, allMethods, 0, parentMethods.length);
System.arraycopy(thisMethods, 0, allMethods, parentMethods.length, thisMethods.length);
thisMethods = allMethods;
}
return thisMethods;
}
protected void doOptions(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
Method[] methods = getAllDeclaredMethods(getClass());
boolean ALLOW_GET = false;
boolean ALLOW_HEAD = false;
boolean ALLOW_POST = false;
boolean ALLOW_PUT = false;
boolean ALLOW_DELETE = false;
boolean ALLOW_TRACE = true;
boolean ALLOW_OPTIONS = true;
for (int i = 0; i < methods.length; ++i) {
Method m = methods[i];
if (m.getName().equals("doGet")) {
ALLOW_GET = true;
ALLOW_HEAD = true;
}
if (m.getName().equals("doPost"))
ALLOW_POST = true;
if (m.getName().equals("doPut"))
ALLOW_PUT = true;
if (m.getName().equals("doDelete"))
ALLOW_DELETE = true;
}
String allow = null;
if ((ALLOW_GET) &&
(allow == null)) allow = "GET";
if (ALLOW_HEAD)
if (allow == null) allow = "HEAD";
else allow = allow + ", HEAD";
if (ALLOW_POST)
if (allow == null) allow = "POST";
else allow = allow + ", POST";
if (ALLOW_PUT)
if (allow == null) allow = "PUT";
else allow = allow + ", PUT";
if (ALLOW_DELETE)
if (allow == null) allow = "DELETE";
else allow = allow + ", DELETE";
if (ALLOW_TRACE)
if (allow == null) allow = "TRACE";
else allow = allow + ", TRACE";
if (ALLOW_OPTIONS)
if (allow == null) allow = "OPTIONS";
else allow = allow + ", OPTIONS";
resp.setHeader("Allow", allow);
}
protected void doTrace(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String CRLF = "/r/n";
String responseString = "TRACE " + req.getRequestURI() + " " + req.getProtocol();
Enumeration reqHeaderEnum = req.getHeaderNames();
while (reqHeaderEnum.hasMoreElements()) {
String headerName = (String)reqHeaderEnum.nextElement();
responseString = responseString + CRLF + headerName + ": " + req.getHeader(headerName);
}
responseString = responseString + CRLF;
int responseLength = responseString.length();
resp.setContentType("message/http");
resp.setContentLength(responseLength);
ServletOutputStream out = resp.getOutputStream();
out.print(responseString);
out.close();
}
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException//http请求的分发者
{
long lastModified;
String method = req.getMethod();
if (method.equals("GET")) {
lastModified = getLastModified(req);
if (lastModified == -1L)
{
doGet(req, resp);
} else {
long ifModifiedSince = req.getDateHeader("If-Modified-Since");
if (ifModifiedSince < lastModified / 1000L * 1000L)
{
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
}
else resp.setStatus(304);
}
}
else if (method.equals("HEAD")) {
lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
}
else if (method.equals("POST")) {
doPost(req, resp);
}
else if (method.equals("PUT")) {
doPut(req, resp);
}
else if (method.equals("DELETE")) {
doDelete(req, resp);
}
else if (method.equals("OPTIONS")) {
doOptions(req, resp);
}
else if (method.equals("TRACE")) {
doTrace(req, resp);
}
else
{
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(501, errMsg);
}
}
private void maybeSetLastModified(HttpServletResponse resp, long lastModified)
{
if (resp.containsHeader("Last-Modified"))
return;
if (lastModified >= 0L)
resp.setDateHeader("Last-Modified", lastModified);
}
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException//是GenericServlet的service的实现，调用重载的service方法
{
HttpServletRequest request;
HttpServletResponse response;
try
{
request = (HttpServletRequest)req;
response = (HttpServletResponse)res;
} catch (ClassCastException e) {
throw new ServletException("non-HTTP request or response");
}
service(request, response);
}
}