关于精简JRE文件之精简rt.jar包

2022-10-25 00:00:00 jar 文件精简

在网络上搜索下便能看到有不少讨论这个问题的文章。个人认为，JRE最好是能向下兼容，于是不同的程序可以在自己的程序中配置所需要的JRE版本。这样就不再会因为用户机器上的JRE版本问题而烦恼。同时，Java开发者所能做的就是尽量精简JRE以满足自己产品运行为最低要求。
本文將介绍我成功简化rt.jar包的过程。
正文：
操作流程简介：
首先，在Windows环境下，准备好需要精简的rt.jar所属的JRE文件夹。
接着，需要在Windows环境下，通过命令在准备好的的JRE环境中运行我们所需要的程序，程序的每个功能最好都能执行，以满足每个需要被调用的包能被自动记录在一个文本文件中。
然后，编写一个程序按照记录將解压缩後的rt.jar包中所需要的类及其所属文件目录结构完整的复制到一个新的rt文件夹中（默认命名为ort(Objecct rt的意思)）。
最后，打包ort文件为rt.jar并替换之前准备好的JRE/lib/ 下的rt.jar文件。（原来的rt.jar文件有40多MB，简化後最小可能只有几MB）。

操作流程详述：

（其中用到了来自网络的程序代码，当然经过我大量修改後才成功执行了任务。由于事隔几日，没有记下原代码作者信息，如果原代码作者看到，可以联系我，我将会加上引用注释）
重新搜索了下，那篇文章被到处引用，如：
http://www.kaiyuan8.org/Article/syaKuiwQVGqhnFgjCwcZ.aspx
http://www.cnitblog.com/Walter/articles/59164.html（仅仅作为举例，别无它意）
已经难寻出处了。
下面来讲讲我根据这篇文章精简的经历吧。

首先，在Windows下准备好for Windows版的完整JRE文件。（我的在C:/Program Files/Java/jdk1.6.0_20/jre，其中jre/bin/中的Java程序是.exe格式的）。所要精简的rt.jar在/jre/lib/目录下。先不拷贝这个jre文件。
我们需要在jre文件见的父文件夹（即，上级文件夹）下创建.txt文本文件，并写入：

start jre/bin/java -jar -verbose:class 【改写成你打包成.jar的产品程序包路径，并去掉这句话两端的中括号】>>usedClasses.txt
pause

再將其.txt修改成.cmd。并执行。

“这样程序使用的就是当前目录下的jre，程序运行后，最好把所有的功能使用一遍，这样输出了一个文件usedClasses.txt，里面有所有需要的class，其格式如下：
[Opened D:\data\dict\jre\lib\rt.jar]
[Loaded java.lang.Object from D:\data\dict\jre\lib\rt.jar]
[Loaded java.io.Serializable from D:\data\dict\jre\lib\rt.jar]
[Loaded java.lang.Comparable from D:\data\dict\jre\lib\rt.jar]
[Loaded java.lang.CharSequence from D:\data\dict\jre\lib\rt.jar]
[Loaded org.apache.lucene.index.CompoundFileReader$FileEntry from file:/D:/data/dict/dict.jar]
我们依照这个文件来裁剪rt.jar：“

由于在Ubuntu下我使用GUN Emacs 23来修改usedClasses.txt文件的内容，以满足之后程序读取的需要（这算是我第一次正式使用Emacs吧）。第一步，我用Gun Emacs 23打开usedClasses.txt文件。
第二步，选择Edit->Replace->Replace String…，键入将被替换的[Loaded 并确认，再键入用于替换它的回车（即，等同于删去[Loaded 这个关键字段）。
第三步，选择Edit->Replace->Replace Regexp…，通过正则表达式from.*来查找from到]的语句。并替换
第四步，删掉最开头的 [Opened 。删掉其他多余的不包含.class类的语句。
第五步，保存文件。这样usedClasses.txt便准备好了。
注释：在Emacs中 `\n’ here doesn’t match a newline; to do that, type C-q C-j instead（C代表Ctrl键）按下Ctrl不放，再接着依次按qj键。(根多关于Emacs可以参考：http://hi.baidu.com/limp_t/blog/item/3bc60f54d868b0143a2935bf.html)

下面修改之前提到的文章中的Java代码。因为我发现他们还不能够成功拷贝二进制文件。
首先，我分享将要用到的，由我封装的IO读写类的部分用到的方法的代码，其他的代码可以省去，足够作为一个完整的类。
然后，我在分享我修改後的拷贝.class文件及其目录结构的代码。

InputOutput.java：

package com.wordpress.iwillaccess.classes.global;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.FileReader;

import java.io.FileWriter;

import java.io.IOException;

public
class InputOutput {

private
static String _fileLocation;

private
static String _fileName;

private
static String _fileDirectory;

private
static String _fileContent;

private
static
byte[] _byte;

/**

*
@return
the _fileDirection

public String get_fileLocation() {

return _fileLocation;

}

/**

*
@return
the _fileName

public String get_fileName() {

return _fileName;

}

/**

*
@return
the _fileDirectory

public String get_fileDirectory() {

return _fileDirectory;

}

/**

*
@return
the _fileContents

public String get_fileContent() {

return _fileContent;

}

/**

*
@return
the _byte

public
byte[] get_byte() {

return _byte;

}

/**

*
@param
fileDirection

* the _fileDirection to set

private
static
synchronized
void set_fileLocation(String fileLocation) {

_fileLocation = fileLocation;

}

/**

*
@param
fileName

* the _fileName to set

private
static
synchronized
void set_fileName(String fileName) {

_fileName = fileName;

}

/**

*
@param
fileLocation

* the _fileLocation to set

*
@param
fileName

* the _fileName to set

*

* fileLocation and fileName is the _fileDirectory to set.

public
synchronized
void set_fileDirectory(String fileLocation,

String fileName) {

set_fileLocation(fileLocation);

set_fileName(fileName);

_fileDirectory = fileLocation + fileName;

}

/**

*
@param
fileDirectory

* the _fileDirectory to set

*

* _fileDirectory = _fileLocation + _fileName;

* _fileLocation and _fileName will be set automatically in this

* method.

public
synchronized
void set_fileDirectory(String fileDirectory) {

set_fileLocation(fileDirectory.substring(
0, fileDirectory

.lastIndexOf(
“/”) +
1));

set_fileName(fileDirectory

.substring(fileDirectory.lastIndexOf(
“/”) +
1));

_fileDirectory = fileDirectory;

}

/**

*
@param
fileContents

* the _fileContents to set

public
synchronized
void set_fileContent(String fileContent) {

_fileContent = fileContent;

}

/**

*
@param
_byte

* the _byte to set

private
synchronized
void set_byte(
byte[] _byte) {

InputOutput._byte = _byte;

}

public InputOutput() {

//
TODO
Auto-generated constructor stub

}

/**

*
check if the file is exist or not

*
@param
fileDirectory

* the _fileDirectory to set, and the directory of the file will

* be checked.

*
@return
true: file is exist;

* false: file is not exist.

public
boolean checkIfFileExist(String fileDirectory) {

set_fileDirectory(fileDirectory);

File file =
new File(get_fileDirectory());

// System.out.println(“file.exists():” + file.exists());

return file.exists();

}

//…………

//……省去的无关方法的代码………

//…………

/**

*
input get_byte() to get_fileDirectory.
If object file is exist, it will

* be replaced without warning.

*

* NOTE:

*
<
blockquote
>
use the set_fileDirectory(), set_byte() and

* checkIfFileExist(String fileDirectory) methods first

* to set a righdis.readFully(b)t file directory and file content

* before using this method;

*
<
blockquote
>

public
synchronized
void DataInputFully() {

if (get_fileLocation() !=
null && get_fileName() !=
null

&& get_fileContent() !=
null && get_byte() !=
null) {

try {

FileOutputStream fos =
new FileOutputStream(get_fileDirectory());

DataOutputStream dos =
new DataOutputStream(fos);

dos.write(get_byte());

dos.close();

}
catch (Exception e) {

e.printStackTrace();

}

}
else {

System.out.println(
“fileLocation:” + get_fileLocation()

+
“; or fileName:” + get_fileName() +
“; or byte[]:”

+ get_byte() +
” is null.”);

}

/**

*
input get_byte() to get_fileDirectory.
If object file is exist, it will

* be replaced without warning.

*

* NOTE:

*
<
blockquote
>
please use set_fileDirectory() to set the file directory,

* and use checkIfFileExist(String fileDirectory) first

* before using this method.

*
</
blockquote
>

*
@param
b

* the _byte to set

public
void DataInputFully(
byte[] b) {

set_byte(b);

DataInputFully();

}

/**

*
input get_byte() to get_fileDirectory.
If object file is exist, it will

* be replaced without warning.

*

* NOTE:

*
<
blockquote
>
create a file, whose directory as
<
code
>
fileDirectory
</
code
>

* and file content as
<
code
>
get_byte()
</
code
>
.

* Use checkIfFileExist(String fileDirectory) first

*
</
blockquote
>

*
@param
fileDirectory

* the _fileDirectory to set

*
@param
b

* the _byte to set, contains the content of file.

public
void DataInputFully(String fileDirectory,
byte[] b) {

set_fileDirectory(fileDirectory);

set_byte(b);

DataInputFully();

}

/**

*
input get_byte() to get_fileDirectory.
If object file is exist, it will

* be replaced without warning.

*

* NOTE:

*
<
blockquote
>
create file named
<
code
>
fileName
</
code
>
in

*
<
code
>
fileLocation
</
code
>
input
<
code
>
get_byte()
</
code
>
to file named as

*
<
code
>
fileName
</
code
>
in
<
code
>
fileLocation
</
code
>
.

* Use checkIfFileExist(String fileDirectory) first

*
</
blockquote
>

*
@param
fileLocation

* the _fileLocation to set and will be used to set the

* _fileDirectory

*
@param
fileName

* the _fileName to set and will be used to set the

* _fileDirectory

*
@param
b

* the _byte to set and will be write to the file with

* _fileDirectory directory. _byte Contains the content of file.

public
void DataInputFully(String fileLocation, String fileName,
byte[] b) {

set_fileDirectory(fileLocation, fileName);

set_byte(b);

DataInputFully();

}

/**

*
Out put a file by using DataOutputStream class.

*

* NOTE:

*
<
blockquote
>
use the set_fileDirectory() method first

* to set a right file directory

* before using this method;

*
</
blockquote
>

*
@return
null:if fileDirectory is null;

* file content byte[];

public
synchronized
byte[] DataOutputFully() {

if (get_fileDirectory() !=
null) {

File file =
new File(get_fileDirectory());

if (file.exists()) {

try {

FileInputStream fis;

fis =
new FileInputStream(get_fileDirectory());

DataInputStream dis =
new DataInputStream(fis);

byte[] b =
new
byte[dis.available()];

while (dis.available() >
0) {

dis.readFully(b);

// System.out.println(” :” + b.length);

}

set_byte(b);

String tmpStr =
“”;

for (
int i =
0; i < b.length; i++) {

tmpStr += String.valueOf(b[i]);

}

set_fileContent(tmpStr);

// System.out.println(“\n” + get_fileContent() + “\n”

// + get_fileLocation() + “\n” + get_fileName());

}
catch (FileNotFoundException e) {

//
TODO
Auto-generated catch block

e.printStackTrace();

}
catch (IOException e) {

//
TODO
Auto-generated catch block

e.printStackTrace();

}
catch (Exception e) {

//
TODO
Auto-generated catch block

e.printStackTrace();

}

return get_byte();

}
else {

System.out.println(
“fileDirectory:” + get_fileDirectory()

+
“; and the file is not exist.”);

return
null;

}

}
else {

System.out.println(
“fileDirectory:” + get_fileDirectory()

+
“; is null”);

return
null;

}

/**

*
Out put a file, which directory as
<
code
>
fileDirectory
</
code
>
,

*
by using DataOutputStream class.

*
@param
fileDirectory

* the _fileDirectory to set and will be used to find the file,

* which is supposed to be opened.

*
@return
byte[] _byte() the content of the chose file.

public
byte[] DataOutputFully(String fileDirectory) {

set_fileDirectory(fileDirectory);

return DataOutputFully();

}

/**

*
Out put a file, which directory as
<
code
>
fileLocation
</
code
>
plus

*

<
code
>
fileName
</
code
>
,

*
by using DataOutputStream class.

*
@param
fileLocation

* the _fileLocation to set and will be used to set the

* _fileDirectory

*
@param
fileName

* the _fileName to set and will be used to set the

* _fileDirectory

*
@return
byte[[] get_byte() the content of the chose file.Data

public
byte[] DataOutputFully(String fileLocation, String fileName) {

set_fileDirectory(fileLocation, fileName);

return DataOutputFully();

}

public
static
void main(String[] args) {

InputOutput io =
new InputOutput();

io.set_fileDirectory(
“/home/knowyourself1010/Tracker.class”);

io.set_fileContent(
“1234567890 abcdefg ABCDEFG 好的繁体字简体字复杂么？”);

// io.DataInput();

System.out.println(io.DataOutput());

io.set_fileDirectory(
“/home/knowyourself1010/file.class”);

io.DataInput();

// io.set_fileContent(“rfgadssssssssssssssdsaaaadwefewfefeferegrqedwdq”);

// System.out.println(io.get_fileContent());

}

CopyUsefulClasses.java:

/**

package com.wordpress.iwillaccess.tools;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.LineNumberReader;

import com.wordpress.iwillaccess.classes.global.InputOutput;

/**

*
@author
knowyourself1010

public
class CopyUsefulClasses {

// 文件拷贝

private
static
boolean copy(String sourceFileLocation,

String objectFileLocation, String fileName) {

try
// must try and catch,otherwise will compile error

{

if (sourceFileLocation.substring(sourceFileLocation.length() –
1) !=
“/”) {

sourceFileLocation +=
“/”;

}

if ((objectFileLocation.substring(objectFileLocation.length() –
1)) !=
“/”) {

objectFileLocation +=
“/”;

}

InputOutput inputOutput =
new InputOutput();

byte[] b = inputOutput

.DataOutputFully(sourceFileLocation, fileName);

inputOutput.DataInputFully(objectFileLocation, fileName, b);

return
true;
// if success then return true

}
catch (Exception e) {

System.out.println(
“Error!”);

return
false;
// if fail then return false

}

// 读取路径,copy

private
static
int dealClass(String needfile, String sdir, String odir)

throws IOException {

int sn =
0;
// 成功个数

if (odir.length() >
0 && sdir.length() >
0) {

if ((sdir.substring(sdir.length() –
1)) !=
“/”) {

sdir +=
“/”;

}

if (odir.substring(odir.length() –
1) !=
“/”) {

odir +=
“/”;

}

File usedclass =
new File(needfile);

if (usedclass.canRead()) {

String line =
null;

LineNumberReader reader =
new LineNumberReader(

new InputStreamReader(
new FileInputStream(usedclass),

“UTF-8”));

while ((line = reader.readLine()) !=
null) {

line = line.trim();

if (line.contains(
“.”) || line.contains(
“/”)) {

// format the direction from package name to path

String dir = line.replace(
“.”,
“/”);

// filter the file name.

String tmpdir = dir.substring(
0, dir.lastIndexOf(
“/”));

String sourceFileLocation = sdir + tmpdir;

String objectFileLocation = odir + tmpdir;

String fileName = dir.substring(

dir.lastIndexOf(
“/”) +
1, dir.length())

+
“.class”;

File fdir =
new File(objectFileLocation);

if (!fdir.exists())

fdir.mkdirs();

boolean copy_ok = copy(sourceFileLocation,

objectFileLocation, fileName);

if (copy_ok)

sn++;

else {

System.out.println(line);

}

}
else {

sn = –
1;

}

return sn;

}

/**

*
@param
args

public
static
void main(String[] args) {

//
TODO
Auto-generated method stub

try {

BufferedReader lineOfText =
null;

// get need classes log file direction

System.out

.println(
“needfile (file logged the full name of useful classes ):”);

lineOfText =
new BufferedReader(
new InputStreamReader(System.in));

String needfile = lineOfText.readLine();

// get source folder direction

System.out

.println(needfile

+
“
\n
Source Folder Direction (the direction of the folder filled the classes need to be filtered.):”);

lineOfText =
new BufferedReader(
new InputStreamReader(System.in));

String sdir = lineOfText.readLine();

// get object folder direction

System.out

.println(sdir

+
“
\n
Object Folder Direction (the direction of the folder used to fill the filtered classes.):”);

lineOfText =
new BufferedReader(
new InputStreamReader(System.in));

String odir = lineOfText.readLine();

System.out.println(odir +
“
\n
“);

int sn = dealClass(needfile, sdir, odir);

System.out.print(sn);

}
catch (IOException e) {

//
TODO
自动生成 catch 块

e.printStackTrace();

}

(在此感谢irc: ##java上朋友提示读写Binary文件的注意事项：不要用Reader方法！Char也不太支持哦。)

运行CopyUsefulClasses.java。首先输入usedClasses.txt的绝对路径，回车，在输入jre/lib/rt.jar解压後的rt文件夹所在的路径，回车，再输入ort(所要存放拷贝过来的有用的.class文件的文件夹)。然后等上几分中，期间会提示，你的产品程序所用到的jre不包含的类不存在，不用管，因为我们呢只拷贝rt文件中的.class文件。
最后將ort文件夹下面的所有文件加压缩为rt.zip文件，并改为rt.jar。
注意：1.是选中ort文件夹下所有子文件夹，而非选中ort文件夹，并压缩。
2.在Ubuntu10.10下如果选择压缩为jar格式文件，可能会少压缩进java.lang.Object.class等文件（估计是个bug），所以需要压缩为.zip再该类型为.jar。

最后，將要简化的jre中的rt.jar替换为这里压缩得到的rt.jar文件。我的只有2MB。
用 java -jar [您的jar程序路径]
来测试简化後的jre是否成功吧。

    原文作者：Housing_person
    原文地址: https://blog.csdn.net/kkkwewewaqsdfas/article/details/11829349
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。

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