Servlet与JSP的关系
JSP被Web容器转换成相应的Servlet的.java文件，在编译成.class文件，然后加载到Web容器中，所以最后提供服务的依然是Servlet
初识Servlet
/**
* 初始Servlet
*/
public class HelloServlet extends HttpServlet {
// 处理POST请求
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
// 处理GET请求
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
String name = request.getParameter("username");
out.print("<h1>" + name + "</h1>");
out.close();
}
}
自定义的Servlet都需要继承HttpServlet，一般只会重写GET、POST方法；这两个方法都是操纵HttpServletRequest和HttpServletResponse对象的引用
Servlet层级关系
Servlet的继承关系，如下图：
Image.png
顶层Servlet接口
public interface Servlet {
void init(ServletConfig config) throws ServletException;
ServletConfig getServletConfig();
void service(ServletRequest req, ServletResponse resp) throws ServletException, IOException;
String getServletInfo();
void destroy();
}
定义Servlet的生命周期：init()、service()、destroy()
可以获取到当前Servlet的配置信息：getServletConfig()，配置信息又封装了当前Servlet上下文信息：getServletContext()
GenericServlet抽象类
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 msg) {
this.getServletContext().log(this.getServletName() + ": " + msg);
}
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();
}
}
GenericServlet不仅实现了Servlet接口还实现了ServletConfig接口，其主要的作用就是实现了init方法、getServletContext方法和getServletConfig方法，其他Servlet就可以直接使用ServletContext对象和ServletConfig了
HttpServlet
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 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 {
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 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 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;
for(int allow = 0; allow < methods.length; ++allow) {
Method m = methods[allow];
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 var13 = null;
if(ALLOW_GET) {
var13 = "GET";
}
if(ALLOW_HEAD) {
if(var13 == null) {
var13 = "HEAD";
} else {
var13 = var13 + ", HEAD";
}
}
if(ALLOW_POST) {
if(var13 == null) {
var13 = "POST";
} else {
var13 = var13 + ", POST";
}
}
if(ALLOW_PUT) {
if(var13 == null) {
var13 = "PUT";
} else {
var13 = var13 + ", PUT";
}
}
if(ALLOW_DELETE) {
if(var13 == null) {
var13 = "DELETE";
} else {
var13 = var13 + ", DELETE";
}
}
if(ALLOW_TRACE) {
if(var13 == null) {
var13 = "TRACE";
} else {
var13 = var13 + ", TRACE";
}
}
if(ALLOW_OPTIONS) {
if(var13 == null) {
var13 = "OPTIONS";
} else {
var13 = var13 + ", OPTIONS";
}
}
resp.setHeader("Allow", var13);
}
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 out = (String)reqHeaderEnum.nextElement();
buffer.append(CRLF).append(out).append(": ").append(req.getHeader(out));
}
buffer.append(CRLF);
int responseLength = buffer.length();
resp.setContentType("message/http");
resp.setContentLength(responseLength);
ServletOutputStream out1 = resp.getOutputStream();
out1.print(buffer.toString());
out1.close();
}
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String method = req.getMethod();
long errMsg;
if(method.equals("GET")) {
errMsg = this.getLastModified(req);
if(errMsg == -1L) {
this.doGet(req, resp);
} else {
long ifModifiedSince;
try {
ifModifiedSince = req.getDateHeader("If-Modified-Since");
} catch (IllegalArgumentException var9) {
ifModifiedSince = -1L;
}
if(ifModifiedSince < errMsg / 1000L * 1000L) {
this.maybeSetLastModified(resp, errMsg);
this.doGet(req, resp);
} else {
resp.setStatus(304);
}
}
} else if(method.equals("HEAD")) {
errMsg = this.getLastModified(req);
this.maybeSetLastModified(resp, errMsg);
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 errMsg1 = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[]{method};
errMsg1 = MessageFormat.format(errMsg1, errArgs);
resp.sendError(501, errMsg1);
}
}
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("non-HTTP request or response");
}
this.service(request, response);
}
}
HttpServlet主要帮我们实现了service方法，当请求来到时，Servlet会调用service()方法，可以看到HttpServlet的service()方法：先判断HTTP的请求方式，在分别调用doGet()、doPost()等方法
ServletContext
public interface ServletContext {
String TEMPDIR = "javax.servlet.context.tempdir";
String ORDERED_LIBS = "javax.servlet.context.orderedLibs";
String getContextPath();
ServletContext getContext(String var1);
int getMajorVersion();
int getMinorVersion();
int getEffectiveMajorVersion();
int getEffectiveMinorVersion();
String getMimeType(String var1);
Set<String> getResourcePaths(String var1);
URL getResource(String var1) throws MalformedURLException;
InputStream getResourceAsStream(String var1);
RequestDispatcher getRequestDispatcher(String var1);
RequestDispatcher getNamedDispatcher(String var1);
/** @deprecated */
Servlet getServlet(String var1) throws ServletException;
/** @deprecated */
Enumeration<Servlet> getServlets();
/** @deprecated */
Enumeration<String> getServletNames();
void log(String var1);
/** @deprecated */
void log(Exception var1, String var2);
void log(String var1, Throwable var2);
String getRealPath(String var1);
String getServerInfo();
String getInitParameter(String var1);
Enumeration<String> getInitParameterNames();
boolean setInitParameter(String var1, String var2);
Object getAttribute(String var1);
Enumeration<String> getAttributeNames();
void setAttribute(String var1, Object var2);
void removeAttribute(String var1);
String getServletContextName();
Dynamic addServlet(String var1, String var2);
Dynamic addServlet(String var1, Servlet var2);
Dynamic addServlet(String var1, Class<? extends Servlet> var2);
<T extends Servlet> T createServlet(Class<T> var1) throws ServletException;
ServletRegistration getServletRegistration(String var1);
Map<String, ? extends ServletRegistration> getServletRegistrations();
javax.servlet.FilterRegistration.Dynamic addFilter(String var1, String var2);
javax.servlet.FilterRegistration.Dynamic addFilter(String var1, Filter var2);
javax.servlet.FilterRegistration.Dynamic addFilter(String var1, Class<? extends Filter> var2);
<T extends Filter> T createFilter(Class<T> var1) throws ServletException;
FilterRegistration getFilterRegistration(String var1);
Map<String, ? extends FilterRegistration> getFilterRegistrations();
SessionCookieConfig getSessionCookieConfig();
void setSessionTrackingModes(Set<SessionTrackingMode> var1);
Set<SessionTrackingMode> getDefaultSessionTrackingModes();
Set<SessionTrackingMode> getEffectiveSessionTrackingModes();
void addListener(String var1);
<T extends EventListener> void addListener(T var1);
void addListener(Class<? extends EventListener> var1);
<T extends EventListener> T createListener(Class<T> var1) throws ServletException;
JspConfigDescriptor getJspConfigDescriptor();
ClassLoader getClassLoader();
void declareRoles(String... var1);
String getVirtualServerName();
}
ServletContext主要的作用就是封装了和整个Web应用环境相关的数据和方法
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