从上面可知调用函数Dalvik_dalvik_system_DexFile_openDexFile来打开Ｄex文件，这个函数的源码如下：
staticvoid Dalvik_dalvik_system_DexFile_openDexFile(const u4* args,
JValue* pResult)
{
StringObject* sourceNameObj =(StringObject*) args[0];
这行是输入的Jar或Ｄex文件名参数。
StringObject* outputNameObj =(StringObject*) args[1];
这行是输出的文件名参数。
int flags = args[2];
这行是处理的标示。
DexOrJar* pDexOrJar = NULL;
JarFile* pJarFile;
RawDexFile* pRawDexFile;
char* sourceName;
char* outputName;
if (sourceNameObj == NULL) {
dvmThrowException("Ljava/lang/NullPointerException;",NULL);
RETURN_VOID();
}
这段代码是当输入文件名称为空对象时，就抛出异常。
sourceName =dvmCreateCstrFromString(sourceNameObj);
这行代码调用函数dvmCreateCstrFromString把java字符串转换Ｃ字符串，由于Ｊava对象表示的字符串并不能立即就使用到Ｃ语言里，所以需要转换才能使用。
if (outputNameObj != NULL)
outputName =dvmCreateCstrFromString(outputNameObj);
else
outputName = NULL;
这段代码是同样把输出字符串转换Ｃ字符串。
/*
* We have to deal with the possibility thatsomebody might try to
* open one of our bootstrap class DEXfiles. The set of dependencies
* will be different, and hence the resultsof optimization might be
* different, which means we'd actually needto have two versions of
* the optimized DEX: one that only knowsabout part of the boot class
* path, and one that knows about everythingin it. The latter might
* optimize field/method accesses based on aclass that appeared later
* in the class path.
*
* We can't let the user-defined classloader open it and start using
* the classes, since the optimized form ofthe code skips some of
* the method and field resolution that wewould ordinarily do, and
* we'd have the wrong semantics.
*
* We have to reject attempts to manuallyopen a DEX file from the boot
* class path. The easiest way to do thisis by filename, which works
* out because variations in name (e.g."/system/framework/./ext.jar")
* result in us hitting a differentdalvik-cache entry. It's also fine
* if the caller specifies their own outputfile.
*/
if(dvmClassPathContains(gDvm.bootClassPath, sourceName)) {
LOGW("Refusing to reopen boot DEX'%s'\n", sourceName);
dvmThrowException("Ljava/io/IOException;",
"Re-opening BOOTCLASSPATH DEXfiles is not allowed");
free(sourceName);
RETURN_VOID();
}
这段代码是判断用户是否加载系统目录下面的Ｄex文件，如果加载就要拒绝这样的操作，因为系统启动时已经加载了一份这样的优化代码，没有必要再次加载一次。
/*
* Try to open it directly as a DEX. Ifthat fails, try it as a Zip
* with a "classes.dex" inside.
*/
if (dvmRawDexFileOpen(sourceName,outputName, &pRawDexFile, false) == 0) {
LOGV("Opening DEX file '%s'(DEX)\n", sourceName);
pDexOrJar = (DexOrJar*)malloc(sizeof(DexOrJar));
pDexOrJar->isDex = true;
pDexOrJar->pRawDexFile = pRawDexFile;
这段代码是尝试加载Ｄex文件，但基本不存在直接加Ｄex文件的情况，因此在函数dvmRawDexFileOpen还是空函数，没有实际的内容。
}else if (dvmJarFileOpen(sourceName, outputName, &pJarFile, false)== 0) {
LOGV("Opening DEX file '%s'(Jar)\n", sourceName);
pDexOrJar = (DexOrJar*)malloc(sizeof(DexOrJar));
pDexOrJar->isDex = false;
pDexOrJar->pJarFile = pJarFile;
这段代码是加载Jar文件，就是从这里加载Dex文件到缓存里。
}else {
LOGV("Unable to open DEX file'%s'\n", sourceName);
dvmThrowException("Ljava/io/IOException;","unable to open DEX file");
}
if (pDexOrJar != NULL) {
pDexOrJar->fileName = sourceName;
这行代码保存文件名称到Dex文件对象里。
/* add to hash table */
u4 hash = dvmComputeUtf8Hash(sourceName);
这行代码通过文件名称计算ＨＡＳＨ串，加速对文件的查找速度。
void* result;
dvmHashTableLock(gDvm.userDexFiles);
result =dvmHashTableLookup(gDvm.userDexFiles, hash, pDexOrJar,
hashcmpDexOrJar, true);
dvmHashTableUnlock(gDvm.userDexFiles);
这段代码添加ＨＡＳＨ表里，以便后面查找使用。
if (result != pDexOrJar) {
LOGE("Pointer has already beenadded?\n");
dvmAbort();
}
pDexOrJar->okayToFree = true;
}else
free(sourceName);
RETURN_PTR(pDexOrJar);
这行代码返回打开的文件对象。
}
这个函数是通过JAVA调用时输入Ｄex文件名称，然后加载Ｄex文件，最后把这个文件名称放到ＨＡＳＨ表里，然后返回打开的对象。