源码阅读:类加载器--DexPathList

DexPathList 是在Android环境中用来加载dex文件以及native库的

构造方法

DexPathList(ClassLoader definingContext, String dexPath,
            String librarySearchPath, File optimizedDirectory, boolean isTrusted) {
        if (definingContext == null) {
            throw new NullPointerException("definingContext == null");
        }

        if (dexPath == null) {
            throw new NullPointerException("dexPath == null");
        }

        if (optimizedDirectory != null) {
            if (!optimizedDirectory.exists())  {
                throw new IllegalArgumentException(
                        "optimizedDirectory doesn't exist: "
                        + optimizedDirectory);
            }

            if (!(optimizedDirectory.canRead()
                            && optimizedDirectory.canWrite())) {
                throw new IllegalArgumentException(
                        "optimizedDirectory not readable/writable: "
                        + optimizedDirectory);
            }
        }

        this.definingContext = definingContext;

        ArrayList<IOException> suppressedExceptions = new ArrayList<IOException>();
        // save dexPath for BaseDexClassLoader
        this.dexElements = makeDexElements(splitDexPath(dexPath), optimizedDirectory,
                                           suppressedExceptions, definingContext, isTrusted);

        // Native libraries may exist in both the system and
        // application library paths, and we use this search order:
        //
        //   1. This class loader's library path for application libraries (librarySearchPath):
        //   1.1. Native library directories
        //   1.2. Path to libraries in apk-files
        //   2. The VM's library path from the system property for system libraries
        //      also known as java.library.path
        //
        // This order was reversed prior to Gingerbread; see http://b/2933456.
        this.nativeLibraryDirectories = splitPaths(librarySearchPath, false);
        this.systemNativeLibraryDirectories =
                splitPaths(System.getProperty("java.library.path"), true);
        this.nativeLibraryPathElements = makePathElements(getAllNativeLibraryDirectories());

        if (suppressedExceptions.size() > 0) {
            this.dexElementsSuppressedExceptions =
                suppressedExceptions.toArray(new IOException[suppressedExceptions.size()]);
        } else {
            dexElementsSuppressedExceptions = null;
        }
    }

构造方法中的操作：

1.将dex文件目录进行解析并保存

2.将系统中native目录进行保存

2.将所有的native存储的so文件封装成element[]进行保存