JSP隐含对象介绍

jsp中一共有9个隐含对象，它们是：

1.application，它是一个实现了ServletContext接口的类的实例，下面是这个接口的代码：

public interface ServletContext
{

public abstract String getContextPath();

public abstract ServletContext getContext(String s);

public abstract int getMajorVersion();

public abstract int getMinorVersion();

public abstract String getMimeType(String s);

public abstract Set getResourcePaths(String s);

public abstract URL getResource(String s)
throws MalformedURLException;

public abstract InputStream getResourceAsStream(String s);

public abstract RequestDispatcher getRequestDispatcher(String s);

public abstract RequestDispatcher getNamedDispatcher(String s);

/**
* @deprecated Method getServlet is deprecated
*/

public abstract Servlet getServlet(String s)
throws ServletException;

/**
* @deprecated Method getServlets is deprecated
*/

public abstract Enumeration getServlets();

/**
* @deprecated Method getServletNames is deprecated
*/

public abstract Enumeration getServletNames();

public abstract void log(String s);

/**
* @deprecated Method log is deprecated
*/

public abstract void log(Exception exception, String s);

public abstract void log(String s, Throwable throwable);

public abstract String getRealPath(String s);

public abstract String getServerInfo();

public abstract String getInitParameter(String s);

public abstract Enumeration getInitParameterNames();

public abstract Object getAttribute(String s);

public abstract Enumeration getAttributeNames();

public abstract void setAttribute(String s, Object obj);

public abstract void removeAttribute(String s);

public abstract String getServletContextName();
}

2.config，它是一个实现了ServletConfig接口的类的实例，ServletConfig接口的代码如下：

public interface ServletConfig
{

public abstract String getServletName();

public abstract ServletContext getServletContext();

public abstract String getInitParameter(String s);

public abstract Enumeration getInitParameterNames();
}

3.out，它是一个继承了JspWriter抽象类的类的实例，JspWriter抽象类的代码如下：

public abstract class JspWriter extends Writer
{

protected JspWriter(int bufferSize, boolean autoFlush)
{
this.bufferSize = bufferSize;
this.autoFlush = autoFlush;
}

public abstract void newLine()
throws IOException;

public abstract void print(boolean flag)
throws IOException;

public abstract void print(char c)
throws IOException;

public abstract void print(int i)
throws IOException;

public abstract void print(long l)
throws IOException;

public abstract void print(float f)
throws IOException;

public abstract void print(double d)
throws IOException;

public abstract void print(char ac[])
throws IOException;

public abstract void print(String s)
throws IOException;

public abstract void print(Object obj)
throws IOException;

public abstract void println()
throws IOException;

public abstract void println(boolean flag)
throws IOException;

public abstract void println(char c)
throws IOException;

public abstract void println(int i)
throws IOException;

public abstract void println(long l)
throws IOException;

public abstract void println(float f)
throws IOException;

public abstract void println(double d)
throws IOException;

public abstract void println(char ac[])
throws IOException;

public abstract void println(String s)
throws IOException;

public abstract void println(Object obj)
throws IOException;

public abstract void clear()
throws IOException;

public abstract void clearBuffer()
throws IOException;

public abstract void flush()
throws IOException;

public abstract void close()
throws IOException;

public int getBufferSize()
{
return bufferSize;
}

public abstract int getRemaining();

public boolean isAutoFlush()
{
return autoFlush;
}

public static final int NO_BUFFER = 0;
public static final int DEFAULT_BUFFER = -1;
public static final int UNBOUNDED_BUFFER = -2;
protected int bufferSize;
protected boolean autoFlush;
}

4.pageContex，它是一个继承了PageContext抽象类的类的实例，PageContext抽象类的代码如下：

public abstract class PageContext extends JspContext
{

public PageContext()
{
}

public abstract void initialize(Servlet servlet, ServletRequest servletrequest, ServletResponse servletresponse, String s, boolean flag, int i, boolean flag1)
throws IOException, IllegalStateException, IllegalArgumentException;

public abstract void release();

public abstract HttpSession getSession();

public abstract Object getPage();

public abstract ServletRequest getRequest();

public abstract ServletResponse getResponse();

public abstract Exception getException();

public abstract ServletConfig getServletConfig();

public abstract ServletContext getServletContext();

public abstract void forward(String s)
throws ServletException, IOException;

public abstract void include(String s)
throws ServletException, IOException;

public abstract void include(String s, boolean flag)
throws ServletException, IOException;

public abstract void handlePageException(Exception exception)
throws ServletException, IOException;

public abstract void handlePageException(Throwable throwable)
throws ServletException, IOException;

public BodyContent pushBody()
{
return null;
}

public ErrorData getErrorData()
{
return new ErrorData((Throwable)getRequest().getAttribute("javax.servlet.error.exception"), ((Integer)getRequest().getAttribute("javax.servlet.error.status_code")).intValue(), (String)getRequest().getAttribute("javax.servlet.error.request_uri"), (String)getRequest().getAttribute("javax.servlet.error.servlet_name"));
}

public static final int PAGE_SCOPE = 1;
public static final int REQUEST_SCOPE = 2;
public static final int SESSION_SCOPE = 3;
public static final int APPLICATION_SCOPE = 4;
public static final String PAGE = "javax.servlet.jsp.jspPage";
public static final String PAGECONTEXT = "javax.servlet.jsp.jspPageContext";
public static final String REQUEST = "javax.servlet.jsp.jspRequest";
public static final String RESPONSE = "javax.servlet.jsp.jspResponse";
public static final String CONFIG = "javax.servlet.jsp.jspConfig";
public static final String SESSION = "javax.servlet.jsp.jspSession";
public static final String OUT = "javax.servlet.jsp.jspOut";
public static final String APPLICATION = "javax.servlet.jsp.jspApplication";
public static final String EXCEPTION = "javax.servlet.jsp.jspException";
}

5.page，类似this指针，是object类的对象，开发中不常用

6.response，它是一个实现了ServletResponse接口的类（其实就是HttpServletResponse）的实例，ServletResponse接口的代码如下：

public interface ServletResponse
{

public abstract String getCharacterEncoding();

public abstract String getContentType();

public abstract ServletOutputStream getOutputStream()
throws IOException;

public abstract PrintWriter getWriter()
throws IOException;

public abstract void setCharacterEncoding(String s);

public abstract void setContentLength(int i);

public abstract void setContentType(String s);

public abstract void setBufferSize(int i);

public abstract int getBufferSize();

public abstract void flushBuffer()
throws IOException;

public abstract void resetBuffer();

public abstract boolean isCommitted();

public abstract void reset();

public abstract void setLocale(Locale locale);

public abstract Locale getLocale();
}

7.session,它是一个实现了HttpSession接口的类的实例，HttpSession接口的代码如下：

public interface HttpSession
{

public abstract long getCreationTime();

public abstract String getId();

public abstract long getLastAccessedTime();

public abstract ServletContext getServletContext();

public abstract void setMaxInactiveInterval(int i);

public abstract int getMaxInactiveInterval();

/**
* @deprecated Method getSessionContext is deprecated
*/

public abstract HttpSessionContext getSessionContext();

public abstract Object getAttribute(String s);

/**
* @deprecated Method getValue is deprecated
*/

public abstract Object getValue(String s);

public abstract Enumeration getAttributeNames();

/**
* @deprecated Method getValueNames is deprecated
*/

public abstract String[] getValueNames();

public abstract void setAttribute(String s, Object obj);

/**
* @deprecated Method putValue is deprecated
*/

public abstract void putValue(String s, Object obj);

public abstract void removeAttribute(String s);

/**
* @deprecated Method removeValue is deprecated
*/

public abstract void removeValue(String s);

public abstract void invalidate();

public abstract boolean isNew();
}

8.exception，它用来处理页面出现的异常，是java.lang.Throwable类的实例

9.request，它是一个实现了ServletRequest接口的类（其实就是HttpServletRequest）的实例，ServletRequest接口的代码如下：

public interface ServletRequest
{

public abstract Object getAttribute(String s);

public abstract Enumeration getAttributeNames();

public abstract String getCharacterEncoding();

public abstract void setCharacterEncoding(String s)
throws UnsupportedEncodingException;

public abstract int getContentLength();

public abstract String getContentType();

public abstract ServletInputStream getInputStream()
throws IOException;

public abstract String getParameter(String s);

public abstract Enumeration getParameterNames();

public abstract String[] getParameterValues(String s);

public abstract Map getParameterMap();

public abstract String getProtocol();

public abstract String getScheme();

public abstract String getServerName();

public abstract int getServerPort();

public abstract BufferedReader getReader()
throws IOException;

public abstract String getRemoteAddr();

public abstract String getRemoteHost();

public abstract void setAttribute(String s, Object obj);

public abstract void removeAttribute(String s);

public abstract Locale getLocale();

public abstract Enumeration getLocales();

public abstract boolean isSecure();

public abstract RequestDispatcher getRequestDispatcher(String s);

/**
* @deprecated Method getRealPath is deprecated
*/

public abstract String getRealPath(String s);

public abstract int getRemotePort();

public abstract String getLocalName();

public abstract String getLocalAddr();

public abstract int getLocalPort();
}

request对象是最常用的内置对象之一，下面介绍一下它的几个常用的方法
假定你的工程名称为projects,你在浏览器中输入请求路径：

http://127.0.0.1:8080/projects/pages/newForm.jsp

(1)request.getContextPath()，得到当前应用的根目录，输出/projects
(2)request.getServletPath()，输出/pages/newForm.jsp
(3)request.getRequestURI()，输出/projects/pages/newForm.jsp
(4)request.getRequestURL()，输出http://127.0.0.1:8080/projects/pages/newForm.jsp
(5)request.getRealPath("/")，输出C:\Tomcat5.0\webapps\projects