问题
Background
I have to contact different kind of Java project with various of build system. Sometimes the directory structure is different from the package hierarchy. So it is difficult to package.
Even if the build system like Maven and Gradle have its own function to pack .jar but it need a qualified internet connection and a giant size of local repository. Hence I usually build the library I need on the desktop in my office. However I spend more time on my laptop which doesn't have such good connection and storage.
Question
Is there a stable, compatible and secure way to make .jar package? Or move those .class file to appropriate directory? (An official and mature open source tool is better)
I am a beginner of Java Language, so any point may be helpful for me.
In order to make it clearly, here I put some examples.
Case 1: If there is a tool which can moving (moving or copying) the .class file in correct directory it should behave as below:
Before operation:
from_root/
├── a.class
├── b.class
├── c.class
├── d.class
├── e.class
└── f.class
Note in each source file(.java) of .class file, there is package announcement(like package org.hello.world; or package org.hello;)
when typing the_tool ./from_root ./to_root in shell
it will become:
to_root/
└── org
└── hello
├── a.class
├── b.class
└── world
├── c.class
├── d.class
├── e.class
└── f.class
Case 2: If there is a tool which can packing correct .jar file from mess .class file directory it should behave as below:
Before operation:
from_root/
├── a.class
├── b.class
├── c.class
├── d.class
├── e.class
└── f.class
when typing pack_tool ./from_root ./to_root/pack.jar in shell
A pack.jar will be generate in ./to_root.
When add it in Java Build Path of Eclipse, it should be imported and called properly, instead of wrong name-space hierarchy .
What I have tried
For some famous 3rd part library (e.g. apache tika)
It is build by maven, and I typed cd /path/to/tika-1.18-src/tika-1.18/ then I typed mvn package.
Unfortunately, it was failed.
However when I typed mvn compile, everything went right.
Then in order to build .jar package, I typed jar cvf ./build/tika-1.18.jar $(find ./ -name org | grep target) in terminal.
However, the structure inside the .jar package was totally wrong. I couldn't use it in my project.
Then I tried find ./ -name org | grep target | parallel cp {} ./build/ -R -f then cd ./build and finally jar cvf ./tika-1.18.jar org.
It worked. However there is some disadvantage of this method.
Shortcoming:
If the some source file(.java file)'s name include 'target', it will cause big trouble.
If different subproject contain same file it will cause conflict. For example here is the conflict information: cp: cannot create directory './build/org/apache/tika/batch': File exists cp: cannot create directory './build/org/apache/tika/language/translate': File exists
This method can only handle the situation which the path of those .class file is partly correct. If all the .class file are located in same directory flatly, it will failed to work.
Another attemption
I tried to put the .class file in correct directory according to its binary content.
For example, org.apache.tika.detect.AutoDetectReader
$ hexdump -C /path/to/here/EncodingDetector.class
00000000 ca fe ba be 00 00 00 33 00 0e 07 00 0a 07 00 0b |.......3........|
00000010 07 00 0c 01 00 06 64 65 74 65 63 74 01 00 54 28 |......detect..T(|
00000020 4c 6a 61 76 61 2f 69 6f 2f 49 6e 70 75 74 53 74 |Ljava/io/InputSt|
00000030 72 65 61 6d 3b 4c 6f 72 67 2f 61 70 61 63 68 65 |ream;Lorg/apache|
00000040 2f 74 69 6b 61 2f 6d 65 74 61 64 61 74 61 2f 4d |/tika/metadata/M|
00000050 65 74 61 64 61 74 61 3b 29 4c 6a 61 76 61 2f 6e |etadata;)Ljava/n|
00000060 69 6f 2f 63 68 61 72 73 65 74 2f 43 68 61 72 73 |io/charset/Chars|
00000070 65 74 3b 01 00 0a 45 78 63 65 70 74 69 6f 6e 73 |et;...Exceptions|
00000080 07 00 0d 01 00 0a 53 6f 75 72 63 65 46 69 6c 65 |......SourceFile|
00000090 01 00 15 45 6e 63 6f 64 69 6e 67 44 65 74 65 63 |...EncodingDetec|
000000a0 74 6f 72 2e 6a 61 76 61 01 00 27 6f 72 67 2f 61 |tor.java..'org/a|
000000b0 70 61 63 68 65 2f 74 69 6b 61 2f 64 65 74 65 63 |pache/tika/detec|
000000c0 74 2f 45 6e 63 6f 64 69 6e 67 44 65 74 65 63 74 |t/EncodingDetect|
000000d0 6f 72 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 4f |or...java/lang/O|
000000e0 62 6a 65 63 74 01 00 14 6a 61 76 61 2f 69 6f 2f |bject...java/io/|
000000f0 53 65 72 69 61 6c 69 7a 61 62 6c 65 01 00 13 6a |Serializable...j|
00000100 61 76 61 2f 69 6f 2f 49 4f 45 78 63 65 70 74 69 |ava/io/IOExcepti|
00000110 6f 6e 06 01 00 01 00 02 00 01 00 03 00 00 00 01 |on..............|
00000120 04 01 00 04 00 05 00 01 00 06 00 00 00 04 00 01 |................|
00000130 00 07 00 01 00 08 00 00 00 02 00 09 |............|
0000013c
In order to compare I used another .class file org.apache.tika.embedder.Embedder
$ hexdump -C ./Embedder.class
00000000 ca fe ba be 00 00 00 33 00 14 07 00 0f 07 00 10 |.......3........|
00000010 07 00 11 01 00 16 67 65 74 53 75 70 70 6f 72 74 |......getSupport|
00000020 65 64 45 6d 62 65 64 54 79 70 65 73 01 00 36 28 |edEmbedTypes..6(|
00000030 4c 6f 72 67 2f 61 70 61 63 68 65 2f 74 69 6b 61 |Lorg/apache/tika|
00000040 2f 70 61 72 73 65 72 2f 50 61 72 73 65 43 6f 6e |/parser/ParseCon|
00000050 74 65 78 74 3b 29 4c 6a 61 76 61 2f 75 74 69 6c |text;)Ljava/util|
00000060 2f 53 65 74 3b 01 00 09 53 69 67 6e 61 74 75 72 |/Set;...Signatur|
00000070 65 01 00 58 28 4c 6f 72 67 2f 61 70 61 63 68 65 |e..X(Lorg/apache|
00000080 2f 74 69 6b 61 2f 70 61 72 73 65 72 2f 50 61 72 |/tika/parser/Par|
00000090 73 65 43 6f 6e 74 65 78 74 3b 29 4c 6a 61 76 61 |seContext;)Ljava|
000000a0 2f 75 74 69 6c 2f 53 65 74 3c 4c 6f 72 67 2f 61 |/util/Set<Lorg/a|
000000b0 70 61 63 68 65 2f 74 69 6b 61 2f 6d 69 6d 65 2f |pache/tika/mime/|
000000c0 4d 65 64 69 61 54 79 70 65 3b 3e 3b 01 00 05 65 |MediaType;>;...e|
000000d0 6d 62 65 64 01 00 76 28 4c 6f 72 67 2f 61 70 61 |mbed..v(Lorg/apa|
000000e0 63 68 65 2f 74 69 6b 61 2f 6d 65 74 61 64 61 74 |che/tika/metadat|
000000f0 61 2f 4d 65 74 61 64 61 74 61 3b 4c 6a 61 76 61 |a/Metadata;Ljava|
00000100 2f 69 6f 2f 49 6e 70 75 74 53 74 72 65 61 6d 3b |/io/InputStream;|
00000110 4c 6a 61 76 61 2f 69 6f 2f 4f 75 74 70 75 74 53 |Ljava/io/OutputS|
00000120 74 72 65 61 6d 3b 4c 6f 72 67 2f 61 70 61 63 68 |tream;Lorg/apach|
00000130 65 2f 74 69 6b 61 2f 70 61 72 73 65 72 2f 50 61 |e/tika/parser/Pa|
00000140 72 73 65 43 6f 6e 74 65 78 74 3b 29 56 01 00 0a |rseContext;)V...|
00000150 45 78 63 65 70 74 69 6f 6e 73 07 00 12 07 00 13 |Exceptions......|
00000160 01 00 0a 53 6f 75 72 63 65 46 69 6c 65 01 00 0d |...SourceFile...|
00000170 45 6d 62 65 64 64 65 72 2e 6a 61 76 61 01 00 21 |Embedder.java..!|
00000180 6f 72 67 2f 61 70 61 63 68 65 2f 74 69 6b 61 2f |org/apache/tika/|
00000190 65 6d 62 65 64 64 65 72 2f 45 6d 62 65 64 64 65 |embedder/Embedde|
000001a0 72 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 4f 62 |r...java/lang/Ob|
000001b0 6a 65 63 74 01 00 14 6a 61 76 61 2f 69 6f 2f 53 |ject...java/io/S|
000001c0 65 72 69 61 6c 69 7a 61 62 6c 65 01 00 13 6a 61 |erializable...ja|
000001d0 76 61 2f 69 6f 2f 49 4f 45 78 63 65 70 74 69 6f |va/io/IOExceptio|
000001e0 6e 01 00 27 6f 72 67 2f 61 70 61 63 68 65 2f 74 |n..'org/apache/t|
000001f0 69 6b 61 2f 65 78 63 65 70 74 69 6f 6e 2f 54 69 |ika/exception/Ti|
00000200 6b 61 45 78 63 65 70 74 69 6f 6e 06 01 00 01 00 |kaException.....|
00000210 02 00 01 00 03 00 00 00 02 04 01 00 04 00 05 00 |................|
00000220 01 00 06 00 00 00 02 00 07 04 01 00 08 00 09 00 |................|
00000230 01 00 0a 00 00 00 06 00 02 00 0b 00 0c 00 01 00 |................|
00000240 0d 00 00 00 02 00 0e |.......|
00000247
What's amazing is the content after "...SourceFile..." is the package location of this class.
It is possible to write a program which can scan every .class file and determine their location in the directory. However, there is Java 9, Java 10 and Java 11 will coming soon. different java version will cause the different binary content of .class files. And it might be different between JDK and OpenJDK. So it is not compatible enough. But on the other hand, it shows that it is possible to determine the package location of a certain .class file without other infomation.
Hope someone can provide some ideas, thanks sincerely!
回答1:
Generally, it is better to fix the build system issues, to generate the correct directory structure in the first place, rather than trying to fix it after the fact. One problem I see, is that classes from different packages may have the same simple name, so if their class files are written to the same flat directory, one of them will overwrite the other and this data loss can not be fixed afterwards.
Generally, the constant pool at the beginning of the class file contains the qualified class name, so it is possible to extract it, but you need to understand the class file structure to pick the right string. The following method will parse a class file and extract the name (in its internal form):
static String getClassName(ByteBuffer buf) {
if(buf.order(ByteOrder.BIG_ENDIAN).getInt()!=0xCAFEBABE) {
throw new IllegalArgumentException("not a valid class file");
}
int minor=buf.getChar(), ver=buf.getChar(), poolSize=buf.getChar();
int[] pool = new int[poolSize];
//System.out.println("version "+ver+'.'+minor);
for(int ix=1; ix<poolSize; ix++) {
String s; int index1=-1, index2=-1;
byte tag = buf.get();
switch(tag) {
default: throw new UnsupportedOperationException(
"unknown pool item type "+buf.get(buf.position()-1));
case CONSTANT_Utf8:
buf.position((pool[ix]=buf.position())+buf.getChar()+2); continue;
case CONSTANT_Module: case CONSTANT_Package: case CONSTANT_Class:
case CONSTANT_String: case CONSTANT_MethodType:
pool[ix]=buf.getChar(); break;
case CONSTANT_FieldRef: case CONSTANT_MethodRef:
case CONSTANT_InterfaceMethodRef: case CONSTANT_NameAndType:
case CONSTANT_InvokeDynamic: case CONSTANT_Dynamic:
case CONSTANT_Integer: case CONSTANT_Float:
buf.position(buf.position()+4); break;
case CONSTANT_Double: case CONSTANT_Long:
buf.position(buf.position()+8); ix++; break;
case CONSTANT_MethodHandle: buf.position(buf.position()+3); break;
}
}
int access = buf.getChar(), thisClass = buf.getChar();
buf.position(pool[pool[thisClass]]);
return decodeString(buf);
}
private static String decodeString(ByteBuffer buf) {
int size=buf.getChar(), oldLimit=buf.limit();
buf.limit(buf.position()+size);
StringBuilder sb=new StringBuilder(size+(size>>1));
while(buf.hasRemaining()) {
byte b=buf.get();
if(b>0) sb.append((char)b);
else {
int b2 = buf.get();
if((b&0xf0)!=0xe0)
sb.append((char)((b&0x1F)<<6 | b2&0x3F));
else {
int b3 = buf.get();
sb.append((char)((b&0x0F)<<12 | (b2&0x3F)<<6 | b3&0x3F));
}
}
}
buf.limit(oldLimit);
return sb.toString();
}
private static final byte CONSTANT_Utf8 = 1, CONSTANT_Integer = 3,
CONSTANT_Float = 4, CONSTANT_Long = 5, CONSTANT_Double = 6,
CONSTANT_Class = 7, CONSTANT_String = 8, CONSTANT_FieldRef = 9,
CONSTANT_MethodRef = 10, CONSTANT_InterfaceMethodRef = 11,
CONSTANT_NameAndType = 12, CONSTANT_MethodHandle = 15,
CONSTANT_MethodType = 16, CONSTANT_Dynamic = 17, CONSTANT_InvokeDynamic = 18,
CONSTANT_Module = 19, CONSTANT_Package = 20;
This can be used to fix a wrong file location like this:
static void checkAndMoveClassFile(Path path) throws IOException {
ByteBuffer bb;
try(FileChannel ch=FileChannel.open(path, StandardOpenOption.READ)) {
bb=ByteBuffer.allocate((int)ch.size());
while(bb.hasRemaining()) ch.read(bb);
bb.flip();
}
String name = getClassName(bb);
Path newPath = path.resolveSibling(name+".class");
if(!path.equals(newPath)) {
System.out.println("moving "+path+" to "+newPath);
Files.createDirectories(newPath.getParent());
Files.move(path, newPath);
}
}
which you can run over a directory easily
Files.list(dirPath)
.filter(p -> p.getFileName().toString().endsWith(".class"))
.forEach(p -> {
try { checkAndMoveClassFile(p); }
catch (IOException ex) { throw new UncheckedIOException(ex); }
});
来源：https://stackoverflow.com/questions/51570090/how-to-correct-a-mess-java-class-file-set-or-generate-a-proper-jar-archive-fro