Data Compression 1 (51), data compression 151

Data Compression 1 (51), data compression 151

1. compress the specified data in a servlet:

PackageCn. hongxing. servlet;

ImportJava. io. ByteArrayOutputStream;

ImportJava. io. IOException;

ImportJava. io. OutputStream;

ImportJava. io. PrintWriter;

ImportJava. io. StringReader;

ImportJava.util.zip. GZIPOutputStream;

ImportJavax. servlet. ServletException;

ImportJavax. servlet. http. HttpServlet;

ImportJavax. servlet. http. HttpServletRequest;

ImportJavax. servlet. http. HttpServletResponse;

Public ClassGzipServletExtendsHttpServlet {

Public VoidDoGet (HttpServletRequest request, HttpServletResponse resp)

ThrowsServletException, IOException {

// Declare the data to be compressed

String str = "Hello, in the memory, declare Hello, Hello, in" +

"In-memory declare a Hello in-memory declare a Hello you" +

"Fortunately, in the memory, declare a <br/> container declaration to be compressed, get to be compressed" +

"The data container Declaration of the byte code of the data to be compressed to obtain the number of bytes to be compressed" +

"The data container of the Data bytecode declares that the data is to be compressed to obtain the data to be compressed" +

"The data containers of bytecode declare that the data is to be compressed to obtain the bytecode of the data to be compressed" +

"Declare a container declaration in the memory that the data is to be compressed to obtain the data to be compressed" +

"Bytecode data ";

// 2: Get the bytecode of the data to be compressed

Byte[] Src = str. getBytes ("UTF-8 ");

// 3: declare a container in the memory

ByteArrayOutputStream destByte =NewByteArrayOutputStream ();

// 4: declare the compressed tool stream and set the compression destination to destByte

GZIPOutputStream zip =NewGZIPOutputStream (destByte );

// 5: Write Data

Zip. write (src );

// 6: Close the compression tool stream

Zip. close ();

System.Err. Println ("size of bytecode before compression:" + src. length );

// 7: Obtain compressed data

Byte[] Dest = destByte. toByteArray ();

System.Err. Println ("Size of the compressed bytecode:" + dest. length );

// 8: The Bytes array after compression must be output.

Resp. setContentType ("text/html; charset = UTF-8 ");

// 9: The byte stream must be used to output information.

OutputStream out = resp. getOutputStream ();

// 10: Notify the browser. This is compressed data and requires the browser to decompress it.

Resp. setHeader ("Content-encoding", "gzip ");

// 11: the length of the compressed data of the notification Browser

Resp. setContentLength (dest. length );

// 10: Output

Out. write (dest );

}

}

2: All pages *. All jsp Compression

There are only two ways to output information:

Respoonse. getWriter ()..[W1]Output Information-response stream. AllJspPage. After compilationJspWriterMethod.

But allJspAll pagesJspWriter, AndJspwriterYesPrintWriter.

Response. getOutputStream ()--Byte stream.

Analysis: If you want to implement full-site compression, first implementServletInResp. getWriterThe output data is compressed.

First, compress one file.

Step 1: Write a Servlet class. Normal output information

: Resp., getWriter (). print (.....);

Public ClassOneServletExtendsHttpServlet {

Public VoidDoGet (HttpServletRequest request, HttpServletResponse response)

ThrowsServletException, IOException {

Response. setContentType ("text/html; charset = UTF-8 ");

PrintWriter out = response. getWriter ();

Out. println ("Hello everyone ");

}

}

Step 2: intercept the above class and encapsulate response in the interception process.

Implementation image class: HttpServletResponseWrapper-
PackageCn. hongxin. filter;

ImportJava. io. IOException;

ImportJavax. servlet. Filter;

ImportJavax. servlet. FilterChain;

ImportJavax. servlet. FilterConfig;

ImportJavax. servlet. ServletException;

ImportJavax. servlet. ServletRequest;

ImportJavax. servlet. ServletResponse;

ImportJavax. servlet. http. HttpServletResponse;

ImportJavax. servlet. http. HttpServletResponseWrapper;

Public ClassGzipFilterImplementsFilter {

Public VoidInit (FilterConfig filterConfig)ThrowsServletException {

}

Public VoidDoFilter (ServletRequest request, ServletResponseresponse,

FilterChain chain)ThrowsIOException, ServletException {

// Declare the MyResponse packaging class

MyResponseresp =NewMyResponse (HttpServletResponse) response );

// When running the program, the encapsulated class must be passed.

Chain. doFilter (request, resp );

}

Public VoidDestroy (){

}

}

// Package HttpSerlvetResponse

ClassMyResponseExtendsHttpServletResponseWrapper {

PublicMyResponse (HttpServletResponse response ){

Super(Response );

}

}

Step 3: to compress data, we must intercept the getwriter method.

Not returnedApacheOfWrtiterObject.

The complete code is as follows:

PackageCn. hongxing. filter;

Public ClassGzipFilterImplementsFilter {

Public VoidInit (FilterConfig filterConfig)ThrowsServletException {

}

Public VoidDoFilter (ServletRequest request, ServletResponseresponse,

FilterChain chain)ThrowsIOException, ServletException {

// Declare the MyResponse packaging class

MyResponseresp =NewMyResponse (HttpServletResponse) response );

// When running the program, the encapsulated class must be passed.

Chain. doFilter (request, resp );

// If the target class is called successfully, the returned result is reading a.txt.

Filefile =NewFile ("d:/a/a.txt ");

// Declare a cached String object

StringBuildersb =NewStringBuilder ();

// Read the file

InputStreamin =NewFileInputStream (file );

Byte[] B =New Byte[1024];

IntLen = 0;

While(Len = in. read (B ))! =-1 ){

Sb. append (NewString (B, 0, len, "UTF-8 "));

}

In. close ();

// Compress into bytes

Byte[] Src = sb. toString (). getBytes ("UTF-8 ");

// Declare the cache container

ByteArrayOutputStreamdestBytes =NewByteArrayOutputStream ();

// Declare the compressed stream

GZIPOutputStreamgzip =NewGZIPOutputStream (destBytes );

// Compress data

Gzip. write (src );

Gzip. close ();

// Obtain compressed data

Byte[] Dest = destBytes. toByteArray ();

System.Err. Println ("before compression:" + src. length );

System.Err. Println ("after compression:" + dest. length );

// Output

// Native response must be used

HttpServletResponseres = (HttpServletResponse) response;

Res. setContentType ("text/html; charset = UTf-8 ");

OutputStreamout = res. getOutputStream ();

Res. setHeader ("Content-encoding", "gzip"); // required

Res. setContentLength (dest. length );

Out. write (dest );

}

Public VoidDestroy (){

}

}

// Package HttpSerlvetResponse

ClassMyResponseExtendsHttpServletResponseWrapper {[W8]

PublicMyResponse (HttpServletResponse response ){

Super(Response );

}

@ Override

PublicPrintWriter getWriter ([W9])ThrowsIOException {

System.Err. Println ("someone wants to get the output stream ");

PrintWriter out =NewPrintWriter [W10] (

NewOutputStreamWriter (

NewFileOutputStream ("d:/a/a.txt"), "UTF-8 "));

ReturnOut;

}

}