在Android N中簽名使用下面的命令就可以了
java -jar signapk.jar platform.x509.pem platform.pk8 app-debug.apk signed.apk
該命令在Android O中會報(bào)錯(cuò)。具體錯(cuò)誤如下。

Exception in thread "main" java.lang.ExceptionInInitializerError
        at org.conscrypt.OpenSSLBIOInputStream.<init>(OpenSSLBIOInputStream.java:34)
        at org.conscrypt.OpenSSLX509Certificate.fromX509PemInputStream(OpenSSLX509Certificate.java:129)
        at org.conscrypt.OpenSSLX509CertificateFactory$1.fromX509PemInputStream(OpenSSLX509CertificateFactory.java:226)
        at org.conscrypt.OpenSSLX509CertificateFactory$1.fromX509PemInputStream(OpenSSLX509CertificateFactory.java:222)
        at org.conscrypt.OpenSSLX509CertificateFactory$Parser.generateItem(OpenSSLX509CertificateFactory.java:100)
        at org.conscrypt.OpenSSLX509CertificateFactory.engineGenerateCertificate(OpenSSLX509CertificateFactory.java:278)
        at java.base/java.security.cert.CertificateFactory.generateCertificate(CertificateFactory.java:355)
        at com.android.signapk.SignApk.readPublicKey(SignApk.java:184)
        at com.android.signapk.SignApk.main(SignApk.java:1007)
Caused by: java.lang.IllegalArgumentException: Failed to load any of the given libraries: [conscrypt_openjdk_jni-windows-x86_64, conscrypt_openjdk_jni]
        at org.conscrypt.NativeLibraryLoader.loadFirstAvailable(NativeLibraryLoader.java:176)
        at org.conscrypt.NativeCryptoJni.init(NativeCryptoJni.java:49)
        at org.conscrypt.NativeCrypto.<clinit>(NativeCrypto.java:53)
        ... 9 more

錯(cuò)誤原因是conscrypt_openjdk_jni-windows-x86_64, conscrypt_openjdk_jni。，也就是conscrypt_openjdk_jni。
這里需要libconscrypt_openjdk_jni.so。
libconscrypt_openjdk_jni.so 在源碼中存在于2個(gè)地方：

1.out/host/linux-x86/lib64
2.prebuilts/sdk/tools/linux/lib64

我這里用的是out/host/linux-x86/lib64下的libconscrypt_openjdk_jni.so 文件，如果1路徑下的報(bào)錯(cuò)就用2路徑下的，大家用的都不一樣。

把需要簽名的app-debug.apk，signapk.jar， platform.x509.pem，platform.pk8，libconscrypt_openjdk_jni.so，放到同一目錄下，例如放到vendor/mediatek/proprietary/packages/apps/xxx，進(jìn)入xxx目錄下后執(zhí)行下面的命令即可。
java -Djava.library.path=. -jar signapk.jar platform.x509.pem platform.pk8 app-debug.apk app_sign.apk

參考鏈接：
Android8.1源碼下對APK進(jìn)行系統(tǒng)簽名
給一個(gè)apk簽系統(tǒng)簽名
如何獲得系統(tǒng)權(quán)限--解決no conscrypt_openjdk_jni in java.library.path錯(cuò)誤
Android 8.0系統(tǒng)給第三方apk進(jìn)行系統(tǒng)簽名（未使用Andriod Studio，在Android系統(tǒng)編譯環(huán)境下簽名）