Servlet与JSP核心编程 ---- 6 -

onehao

浏览: 13425 次
性别:
来自: 北京

最近访客更多访客>>

博主相关

博客

微博

相册

留言

关于我

文章分类

社区版块

存档分类

Servlet与JSP核心编程 ---- 6

编程 Servlet JSP Excel 浏览器

第七章服务器响应的生成：HTTP响应报头

1.任意响应报头的设置

public void setHeader(String headerName,

String headerValue)

– 设定任意的报头

public void setDateHeader(String name,

long millisecs)

– 将自1970年以来的毫秒数转换成GMT格式日期字符串

public void setIntHeader(String name,

int headerValue)

– 可以省去在调用setHeader之前将int转换成字符串的麻

烦

addHeader, addDateHeader, addIntHeader

– 增加新报头，而非替换已有的报头

2.普通响应报头的设置

setContentType

– 设定Content-Type报头。

– servlet几乎总会用到这个报头。

– 参见常见MIME类型的表格。

• setContentLength

– 设定Content-Length报头。

– 用于持续性HTTP连接。

– 参见Connection请求报头。

• addCookie

– 为Set-Cookie报头增加一个值。

– 参见介绍cookie的部分。

• sendRedirect

– 设定Location报头(以及改变状态代码)。

3.常见MIME类型

类型含意

application/msword Microsoft Word document

application/octet-stream Unrecognized or binary data

application/pdf Acrobat (.pdf) file

application/postscript PostScript file

application/vnd.ms-excel Excel spreadsheet

application/vnd.ms-powerpoint Powerpoint presentation

application/x-gzip Gzip archive

application/x-java-archive JAR file

application/x-java-vm Java bytecode (.class) file

application/zip Zip archive

audio/basic S ound file in .au or .snd format

audio/x-aiff AIFF sound file

audio/x-wav Microsoft Windows sound file

audio/midi MIDI sound file

text/css HTML cascading style sheet

text/html HTML document

text/plain Plain text

text/xml XML document

image/gif GIF image

image/jpeg JPEG image

image/png PNG image

image/tiff TIFF image

video/mpeg MPEG video clip

video/quicktime QuickTime video clip

4.常见HTTP 1.1响应报头

• Cache-Control (1.1) 和Pragma (1.0)

– no-cache值阻止浏览器缓存页面。

• Content-Disposition

– 通过这个报头，可以请求浏览器询问用户将响应存储到磁盘上

给定名称的文件中。

Content-Disposition: attachment; filename=file-name

• Content-Encoding

– 文档的编码方式。参见之前压缩的例子。

• Content-Length

– 响应中的字节数。

– 参见前面幻灯片中的setContentLength。

– 使用ByteArrayOutputStream在发送文档前对文档进行缓冲，这

样才能够确定数据的大小。参见有关Connection请求报头的讨

论。

• Content-Type

– 返回文档时所采用的MIME类型。

– 使用setContentType设置这个报头。

• Expires

– 特定的一段时间，这段时间后应该将文档认作是过期

，不应该再继续缓存。

– 使用setDateHeader设置这个报头。

• Last-Modified

– 文档最后被改动的时间。

– 不要直接设置这个报头；而应该提供getLastModified

方法。参见书中的博彩数字的例子（第3章）。

• Location

– 浏览器应该重新连接到的URL。

– 不要直接设置这个报头，而要使用sendRedirect进行设

定。

• Refresh

– 多少秒后浏览器应该重新载入页面。同时还可以包括

应该连接到的URL。参见后面的例子。

• Set-Cookie

– 浏览器应该记下来的cookie。不要直接设置这个报头

；而应该使用addCookie。参见下一节。

• WWW-Authenticate

– 授权的类型和范围需要在Authorization报头中给出。

参见More Servlets & JSP 中有关安全的章节。

You use the shorthand

setContentType method to set the Content-Type header, and the MIME type

for Excel spreadsheets is application/vnd.ms-excel. So, to generate Excel

spreadsheets, just do:

response.setContentType("application/vnd.ms-excel");
PrintWriter out = response.getWriter();

package coreservlets;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
/** Servlet that creates Excel spreadsheet comparing
* apples and oranges.
*/
public class ApplesAndOranges extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("application/vnd.ms-excel");
PrintWriter out = response.getWriter();
out.println("\tQ1\tQ2\tQ3\tQ4\tTotal");
out.println("Apples\t78\t87\t92\t29\t=SUM(B2:E2)");
out.println("Oranges\t77\t86\t93\t30\t=SUM(B3:E3)");
}
}

处理长时间运行的servlet时我们需要下述内容：

• 不同请求间存储数据的方式。

– 对于不专门针对任意某个客户的数据，可以将它存储在servlet

的字段中（实例变量）。

– 对于专属于某个用户的数据，则要将它存储在HttpSession对象

中。

• 参见随后有关会话跟踪的课程。

– 对于需要为其他servlet或JSP页面访问的数据（和用户无关），

可将其存储到ServletContext中。

• 在响应发送给用户之后，保持计算继续运行的方法。

– 这项任何比较简单：启动一个线程。唯一要注意的是：将线程

的优先级设为比较低的值，这样才不会拖慢整个服务器的运行

。

• 在更新结果就绪后将它们发送给浏览器的方法。

– 使用Refresh报头告诉浏览器，让它请求更新。

使用servlet生成JPEG图像

1. 创建一个BufferedImage

2. 在BufferedImage上绘制内容

3. 设置Content-Type响应报头

response.setContentType("image/jpeg");

4. 获取输出流

OutputStream out = response.getOutputStream

5. 以JPEG格式将BufferedImage发送到输出流

try {
ImageIO.write(image, "jpg", out);
} catch(IOException ioe) {
System.err.println("Error writing JPEG file: "
+ ioe);
}

package coreservlets;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
/** Servlet that generates JPEG images representing
* a designated message with an oblique-shadowed
* version behind it.
*/
public class ShadowedText extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String wantsList = request.getParameter("showList");
if (wantsList != null) {
showFontList(response);
} else {
String message = request.getParameter("message");
if ((message == null) || (message.length() == 0)) {
message = "Missing 'message' parameter";
}
String fontName = request.getParameter("fontName");
if ((fontName == null) || (fontName.length() == 0)) {
fontName = "Serif";
}
String fontSizeString = request.getParameter("fontSize");
int fontSize;
try {
fontSize = Integer.parseInt(fontSizeString);
} catch(NumberFormatException nfe) {
fontSize = 90;
}
response.setContentType("image/jpeg");
MessageImage.writeJPEG
(MessageImage.makeMessageImage(message,
fontName,
fontSize),
response.getOutputStream());
}
}private void showFontList(HttpServletResponse response)
throws IOException {
PrintWriter out = response.getWriter();
String docType =
"<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
"Transitional//EN\">\n";
String title = "Fonts Available on Server";
out.println(docType +
"<HTML>\n" +
"<HEAD><TITLE>" + title + "</TITLE></HEAD>\n" +
"<BODY BGCOLOR=\"#FDF5E6\">\n" +
"<H1 ALIGN=CENTER>" + title + "</H1>\n" +
"<UL>");
String[] fontNames = MessageImage.getFontNames();
for(int i=0; i<fontNames.length; i++) {
out.println(" <LI>" + fontNames[i]);
}
out.println("</UL>\n" +
"</BODY></HTML>");
}
}

package coreservlets;
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;
/** Utilities for building images showing shadowed messages.
* <P>
* Requires JDK 1.4 since it uses the ImageIO class.
* JDK 1.4 is standard with J2EE-compliant app servers
* with servlets 2.4 and JSP 2.0. However, standalone
* servlet/JSP engines require only JDK 1.3 or later, and
* version 2.3 of the servlet spec requires only JDK
* 1.2 or later. So, although most servers run on JDK 1.4,
* this code is not necessarily portable across all servers.
*/
public class MessageImage {
/** Creates an Image of a string with an oblique
* shadow behind it. Used by the ShadowedText servlet.
*/
public static BufferedImage makeMessageImage(String message,
String fontName,
int fontSize) {
Font font = new Font(fontName, Font.PLAIN, fontSize);
FontMetrics metrics = getFontMetrics(font);
int messageWidth = metrics.stringWidth(message);
int baselineX = messageWidth/10;
int width = messageWidth+2*(baselineX + fontSize);
int height = fontSize*7/2;
int baselineY = height*8/10;
BufferedImage messageImage =
new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = (Graphics2D)messageImage.getGraphics();
g2d.setBackground(Color.white);
g2d.clearRect(0, 0, width, height);
g2d.setFont(font);
g2d.translate(baselineX, baselineY);
g2d.setPaint(Color.lightGray);
AffineTransform origTransform = g2d.getTransform();
g2d.shear(-0.95, 0);
g2d.scale(1, 3);
g2d.drawString(message, 0, 0);
g2d.setTransform(origTransform);
g2d.setPaint(Color.black);
g2d.drawString(message, 0, 0);
return(messageImage);
}
public static void writeJPEG(BufferedImage image,
OutputStream out) {
try {
ImageIO.write(image, "jpg", out);
} catch(IOException ioe) {
System.err.println("Error outputting JPEG: " + ioe);
}
}
public static void writeJPEG(BufferedImage image,
File file) {
try {
ImageIO.write(image, "jpg", file);
} catch(IOException ioe) {
System.err.println("Error writing JPEG file: " + ioe);
}
}
public static String[] getFontNames() {
GraphicsEnvironment env =
GraphicsEnvironment.getLocalGraphicsEnvironment();
return(env.getAvailableFontFamilyNames());
}
/** We need a Graphics object to get a FontMetrics object
* (an object that says how big strings are in given fonts).
* But, you need an image from which to derive the Graphics
* object. Since the size of the "real" image will depend on
* how big the string is, we create a very small temporary
* image first, get the FontMetrics, figure out how
* big the real image should be, then use a real image
* of that size.
*/
private static FontMetrics getFontMetrics(Font font) {
BufferedImage tempImage =
new BufferedImage(1, 1, BufferedImage.TYPE_INT_RGB);
Graphics2D g2d = (Graphics2D)tempImage.getGraphics();
return(g2d.getFontMetrics(font));
}
}

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD><TITLE>JPEG Generation Service</TITLE></HEAD>
<BODY BGCOLOR="#FDF5E6">
<H1 ALIGN="CENTER">JPEG Generation Service</H1>
Welcome to the <I>free</I> trial edition of our JPEG
generation service. Enter a message, a font name,
and a font size below, then submit the form. You will
be returned a JPEG image showing the message in the
designated font, with an oblique "shadow" of the message
behind it. Once you get an image you are satisfied with,
right-click
on it (or click while holding down the SHIFT key) to save
it to your local disk.
<P>
The server is currently on Windows, so the font name must
be either a standard Java font name (e.g., Serif, SansSerif,
or Monospaced) or a Windows font name (e.g., Arial Black).
Unrecognized font names will revert to Serif. Press the
"Show Font List" button for a complete list.
<FORM ACTION="/servlet/coreservlets.ShadowedText">
<CENTER>
Message:
<INPUT TYPE="TEXT" NAME="message"><BR>
Font name:
<INPUT TYPE="TEXT" NAME="fontName" VALUE="Serif"><BR>
Font size:
<INPUT TYPE="TEXT" NAME="fontSize" VALUE="90"><P>
<INPUT TYPE="SUBMIT" VALUE="Build Image"><P>
<INPUT TYPE="SUBMIT" NAME="showList" VALUE="Show Font List">
</CENTER>
</FORM>
</BODY></HTML>

package coreservlets;
import java.io.*;
public class ImageTest {
public static void main(String[] args) {
String message = "Testing";
String font = "Arial";
if (args.length > 0) {
message = args[0];
}
if (args.length > 1) {
font = args[1];
}
MessageImage.writeJPEG
(MessageImage.makeMessageImage(message, font, 40),
new File("ImageTest.jpg"));
}
}