Java及Android类加载机制学习笔记

public class PathClassLoader extends BaseDexClassLoader {
    
    public PathClassLoader(String dexPath, ClassLoader parent) {
        super(dexPath, null, null, parent);
    }
    
    public PathClassLoader(String dexPath, String librarySearchPath, ClassLoader parent) {
        super(dexPath, null, librarySearchPath, parent);
    }
}

public class DexClassLoader extends BaseDexClassLoader {
   public DexClassLoader(String dexPath, String optimizedDirectory,
            String librarySearchPath, ClassLoader parent) {
        super(dexPath, new File(optimizedDirectory), librarySearchPath, parent);
    }
}

public BaseDexClassLoader(String dexPath, File optimizedDirectory,
            String libraryPath, ClassLoader parent) {
        super(parent);
        this.pathList = new DexPathList(this, dexPath, libraryPath, optimizedDirectory);
    }

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        List<Throwable> suppressedExceptions = new ArrayList<Throwable>();
        Class c = pathList.findClass(name, suppressedExceptions);
        if (c == null) {
            ClassNotFoundException cnfe = new ClassNotFoundException("Didn't find class \"" + name + "\" on path: " + pathList);
            for (Throwable t : suppressedExceptions) {
                cnfe.addSuppressed(t);
            }
            throw cnfe;
        }
        return c;
    }
}

final class DexPathList {
    public DexPathList(ClassLoader definingContext, String dexPath,
            String libraryPath, File optimizedDirectory) {
        // ... 省略
        // save dexPath for BaseDexClassLoader
        this.dexElements = makePathElements(splitDexPath(dexPath), optimizedDirectory,
                                            suppressedExceptions);
        // ... 省略
    }
    private static Element[] makePathElements(List<File> files, File optimizedDirectory,
                                              List<IOException> suppressedExceptions) {
        List<Element> elements = new ArrayList<>();
        for (File file : files) {
            File zip = null;
            File dir = new File("");
            DexFile dex = null;
            String path = file.getPath();
            String name = file.getName();
            if (path.contains(zipSeparator)) {
                String split[] = path.split(zipSeparator, 2);
                zip = new File(split[0]);
                dir = new File(split[1]);
            } else if (file.isDirectory()) {
                elements.add(new Element(file, true, null, null));
            } else if (file.isFile()) {
                if (name.endsWith(DEX_SUFFIX)) {
                    try {
                        dex = loadDexFile(file, optimizedDirectory);
                    } catch (IOException ex) {
                        System.logE("Unable to load dex file: " + file, ex);
                    }
                } else {
                    zip = file;

                    try {
                        dex = loadDexFile(file, optimizedDirectory);
                    } catch (IOException suppressed) {
                        suppressedExceptions.add(suppressed);
                    }
                }
            } else {
                System.logW("ClassLoader referenced unknown path: " + file);
            }
            if ((zip != null) || (dex != null)) {
                elements.add(new Element(dir, false, zip, dex));
            }
        }
        return elements.toArray(new Element[elements.size()]);
    }
    private static DexFile loadDexFile(File file, File optimizedDirectory)
            throws IOException {
        if (optimizedDirectory == null) {
            return new DexFile(file);
        } else {
            String optimizedPath = optimizedPathFor(file, optimizedDirectory);
            return DexFile.loadDex(file.getPath(), optimizedPath, 0);
        }
    }
}

public final class DexFile {    
    /**
     * Opens a DEX file from a given filename. This will usually be a ZIP/JAR
     * file with a "classes.dex" inside.
     *
     * The VM will generate the name of the corresponding file in
     * /data/dalvik-cache and open it, possibly creating or updating
     * it first if system permissions allow.  Don't pass in the name of
     * a file in /data/dalvik-cache, as the named file is expected to be
     * in its original (pre-dexopt) state.
     *
     * @param fileName
     *            the filename of the DEX file
     *
     * @throws IOException
     *             if an I/O error occurs, such as the file not being found or
     *             access rights missing for opening it
     */
    public DexFile(String fileName) throws IOException {
        mCookie = openDexFile(fileName, null, 0);
        mFileName = fileName;
        guard.open("close");
    }

    private DexFile(String sourceName, String outputName, int flags) throws IOException {
        if (outputName != null) {
            try {
                String parent = new File(outputName).getParent();
                if (Libcore.os.getuid() != Libcore.os.stat(parent).st_uid) {
                    throw new IllegalArgumentException("Optimized data directory " + parent
                            + " is not owned by the current user. Shared storage cannot protect"
                            + " your application from code injection attacks.");
                }
            } catch (ErrnoException ignored) {
            }
        }

        mCookie = openDexFile(sourceName, outputName, flags);
        mFileName = sourceName;
        guard.open("close");
    }
    // ... 省略
    static public DexFile loadDex(String sourcePathName, String outputPathName,
        int flags) throws IOException {
        return new DexFile(sourcePathName, outputPathName, flags);
    }
}