Servlet接口与GenericServlet类以及HttpServlet类的继承关系
Servlet接口与GenericServlet类以及HttpServlet类的继承关系
Servlet接口：
Servlet是一个接口，其中声明了一些Servlet的相关方法：
package javax.servlet;
import java.io.IOException;
public interface Servlet {
void init(ServletConfig var1) throws ServletException;
ServletConfig getServletConfig();
void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
String getServletInfo();
void destroy();
}
GenericServlet类
GenericServlet类是一个抽象类，它实现了Servlet接口。
当然他实现了Servlet中声明的所有方法，不过源码中显示，所有的方法都只是空实现。而且其中的Service方法还是一个抽象方法，等待被其他继承它的类去进一步实现。
package javax.servlet;
import java.io.IOException;
import java.io.Serializable;
import java.util.Enumeration;
public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {
private static final long serialVersionUID = 1L;
private transient ServletConfig config;
public GenericServlet() {
}
public void destroy() {
}
public String getInitParameter(String name) {
return this.getServletConfig().getInitParameter(name);
}
public Enumeration<String> getInitParameterNames() {
return this.getServletConfig().getInitParameterNames();
}
public ServletConfig getServletConfig() {
return this.config;
}
public ServletContext getServletContext() {
return this.getServletConfig().getServletContext();
}
public String getServletInfo() {
return "";
}
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
public void init() throws ServletException {
}
public void log(String message) {
this.getServletContext().log(this.getServletName() + ": " + message);
}
public void log(String message, Throwable t) {
this.getServletContext().log(this.getServletName() + ": " + message, t);
}
public abstract void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
public String getServletName() {
return this.config.getServletName();
}
}
HttpServlet类
这个类算是写Servlet最常用的实现类。
这个类继承了GenericServlet类，并且中进一步实现了GenericServlet类中的抽象方法——Service方法。
并且在Service方法中加入了对不同请求类型的判断，所以使用者只需要重写相应的请求方式所对应的方法即可。比如使用的是Get请求，那么我们只需要重写doGet方法即可。
package javax.servlet.http;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
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 {
private static final long serialVersionUID = 1L;
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 final ResourceBundle lStrings = ResourceBundle.getBundle("javax.servlet.http.LocalStrings");
public HttpServlet() {
}
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String msg = lStrings.getString("http.method_get_not_supported");
this.sendMethodNotAllowed(req, resp, msg);
}
protected long getLastModified(HttpServletRequest req) {
return -1L;
}
protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {
this.doGet(req, resp);
} else {
NoBodyResponse response = new NoBodyResponse(resp);
this.doGet(req, response);
response.setContentLength();
}
}
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String msg = lStrings.getString("http.method_post_not_supported");
this.sendMethodNotAllowed(req, resp, msg);
}
protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String msg = lStrings.getString("http.method_put_not_supported");
this.sendMethodNotAllowed(req, resp, msg);
}
protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String msg = lStrings.getString("http.method_delete_not_supported");
this.sendMethodNotAllowed(req, resp, msg);
}
private void sendMethodNotAllowed(HttpServletRequest req, HttpServletResponse resp, String msg) throws IOException {
String protocol = req.getProtocol();
if (protocol.length() != 0 && !protocol.endsWith("0.9") && !protocol.endsWith("1.0")) {
resp.sendError(405, msg);
} else {
resp.sendError(400, msg);
}
}
private static Method[] getAllDeclaredMethods(Class<?> c) {
if (c.equals(HttpServlet.class)) {
return null;
} else {
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(this.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;
Class clazz = null;
try {
clazz = Class.forName("org.apache.catalina.connector.RequestFacade");
Method getAllowTrace = clazz.getMethod("getAllowTrace", (Class[])null);
ALLOW_TRACE = (Boolean)getAllowTrace.invoke(req, (Object[])null);
} catch (NoSuchMethodException | SecurityException | IllegalAccessException | IllegalArgumentException | InvocationTargetException | ClassNotFoundException var14) {
}
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 = "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";
StringBuilder buffer = (new StringBuilder("TRACE ")).append(req.getRequestURI()).append(" ").append(req.getProtocol());
Enumeration reqHeaderEnum = req.getHeaderNames();
while(reqHeaderEnum.hasMoreElements()) {
String headerName = (String)reqHeaderEnum.nextElement();
buffer.append(CRLF).append(headerName).append(": ").append(req.getHeader(headerName));
}
buffer.append(CRLF);
int responseLength = buffer.length();
resp.setContentType("message/http");
resp.setContentLength(responseLength);
ServletOutputStream out = resp.getOutputStream();
out.print(buffer.toString());
out.close();
}
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String method = req.getMethod();
long lastModified;
if (method.equals("GET")) {
lastModified = this.getLastModified(req);
if (lastModified == -1L) {
this.doGet(req, resp);
} else {
long ifModifiedSince;
try {
ifModifiedSince = req.getDateHeader("If-Modified-Since");
} catch (IllegalArgumentException var9) {
ifModifiedSince = -1L;
}
if (ifModifiedSince < lastModified / 1000L * 1000L) {
this.maybeSetLastModified(resp, lastModified);
this.doGet(req, resp);
} else {
resp.setStatus(304);
}
}
} else if (method.equals("HEAD")) {
lastModified = this.getLastModified(req);
this.maybeSetLastModified(resp, lastModified);
this.doHead(req, resp);
} else if (method.equals("POST")) {
this.doPost(req, resp);
} else if (method.equals("PUT")) {
this.doPut(req, resp);
} else if (method.equals("DELETE")) {
this.doDelete(req, resp);
} else if (method.equals("OPTIONS")) {
this.doOptions(req, resp);
} else if (method.equals("TRACE")) {
this.doTrace(req, resp);
} else {
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[]{
method};
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(501, errMsg);
}
}
private void maybeSetLastModified(HttpServletResponse resp, long lastModified) {
if (!resp.containsHeader("Last-Modified")) {
if (lastModified >= 0L) {
resp.setDateHeader("Last-Modified", lastModified);
}
}
}
public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
try {
request = (HttpServletRequest)req;
response = (HttpServletResponse)res;
} catch (ClassCastException var6) {
throw new ServletException(lStrings.getString("http.non_http"));
}
this.service(request, response);
}
}