6/03/2019

Linux ate ram as disk cache

One day QA asked why memory was really low in QA linux server. Really not sure, this question is interesting for me, as known, our java applications always configured memory limitation, shouldn't happen low memory issue.

From result of "free -m" command executed and checked, If you just naively look at "used" and "free", you'll think your ram is 98/99% full.

Googling that situation, linuxatemyram, what's going on?
Linux is borrowing unused memory for disk caching. This makes it looks like you are low on memory, but everything is fine. Try to use unused memory as disk caching makes the system much faster and more responsive.

If you deeply read "linux ate ram", don't panic, your ram is fine. ^^!

5/22/2019

httpstat - curl statisticsmade simple

Sometimes need to measure RESTful Api to clarify network and server processing capabilities in customer side. httpstat tool that visualizes curl statistics in a way of beauty and clarity.

macOS install

brew install httpstat

curl statistics

httpstat www.google.com

httpstat site

https://github.com/reorx/httpstat

4/19/2019

Disable encoding URL Using RestTemplate in Spring

The RestTemplate is smart to convert the URL with specific characters to URL encoded. But sometimes, we need to disable URL encoding in order to some specific characters are available on server side as its business requirement.
It's a legacy web service and bad design, but customer don't want to change for some reasons.

Disable Encoding URL

Set encoding encoding mode when initialing rest template.

DefaultUriBuilderFactory defaultUriBuilderFactory = new DefaultUriBuilderFactory();
defaultUriBuilderFactory.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.NONE);
      
RestTemplate restTemplate = new RestTemplate();
restTemplate.setUriTemplateHandler(defaultUriBuilderFactory);

Using other encoding mode to satisfy different integration strategies.

TEMPLATE_AND_VALUES, VALUES_ONLY, URI_COMPONENT, NONE

4/10/2019

3 Type of Timeouts in Http client

There are three type of timeouts in Http Client which could be considered to be adjusted when encountering unreliable destination endpoint.

  1. ConnectionTimeout
    Set the timeout in milliseconds used when requesting a connection from the connection manager.
  2. ConnectionRequestTimeout
    Determines the timeout in milliseconds until a connection is established. A timeout value of zero is interpreted as an infinite timeout.
  3. SocketTimeout
    Determines the socket timeout (SO_TIMEOUT) in milliseconds, which is the timeout for waiting for data or, put differently, a maximum period inactivity between two consecutive data packets).

2/19/2019

Import a SSL certificate into a JVM

Sometimes, it's inevitable that HTTPs is only provided, or you are unable to change third part code to ignore certificate verification.

How to import a certificate into a JVM? Here are some steps.

Step1. Fetch the certificate

openssl s_client -connect youtube.com:443 < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > youtube.crt

Step2. Import the certificate

keytool -import -alias youtube.com -keystore /Users/chliu/.sdkman/candidates/java/current/jre/lib/security/cacerts -file youtube.crt
Enter keystore password:<changeit>
Owner: CN=*.google.com, O=Google LLC, L=Mountain View, ST=California, C=US
Issuer: CN=Google Internet Authority G3, O=Google Trust Services, C=US
Serial number: 3b6e50a1d2080062
Valid from: Tue Jan 29 22:58:00 CST 2019 until: Tue Apr 23 22:58:00 CST 2019
Certificate fingerprints:
     MD5:  19:0D:FC:58:69:85:29:59:C4:42:71:05:21:EA:B4:2E
     SHA1: E4:A8:7B:F5:3E:9A:17:4A:E2:9F:26:8F:81:23:78:E3:15:08:85:99
     SHA256: F7:EE:A9:17:44:FD:5D:E8:09:73:4D:97:85:E4:7E:AE:FA:73:6D:6F:31:36:55:0B:07:1B:15:68:D8:81:A3:C8
Signature algorithm name: SHA256withRSA
Subject Public Key Algorithm: 2048-bit RSA key
Version: 3

Extensions:

#1: ObjectId: 1.3.6.1.5.5.7.1.1 Criticality=false
AuthorityInfoAccess [
  [
   accessMethod: caIssuers
   accessLocation: URIName: http://pki.goog/gsr2/GTSGIAG3.crt
,
   accessMethod: ocsp
   accessLocation: URIName: http://ocsp.pki.goog/GTSGIAG3
]
]

#2: ObjectId: 2.5.29.35 Criticality=false
AuthorityKeyIdentifier [
KeyIdentifier [
0000: 77 C2 B8 50 9A 67 76 76   B1 2D C2 86 D0 83 A0 7E  w..P.gvv.-......
0010: A6 7E BA 4B                                        ...K
]
]

#3: ObjectId: 2.5.29.19 Criticality=true
BasicConstraints:[
  CA:false
  PathLen: undefined
]

#4: ObjectId: 2.5.29.31 Criticality=false
CRLDistributionPoints [
  [DistributionPoint:
     [URIName: http://crl.pki.goog/GTSGIAG3.crl]
]]

#5: ObjectId: 2.5.29.32 Criticality=false
CertificatePolicies [
  [CertificatePolicyId: [1.3.6.1.4.1.11129.2.5.3]
[]  ]
  [CertificatePolicyId: [2.23.140.1.2.2]
[]  ]
]

#6: ObjectId: 2.5.29.37 Criticality=false
ExtendedKeyUsages [
  serverAuth
]

#7: ObjectId: 2.5.29.17 Criticality=false
SubjectAlternativeName [
  DNSName: *.google.com
  DNSName: *.android.com
  DNSName: *.appengine.google.com
  DNSName: *.cloud.google.com
  DNSName: *.g.co
  DNSName: *.gcp.gvt2.com
  DNSName: *.ggpht.cn
  DNSName: *.google-analytics.com
  DNSName: *.google.ca
  DNSName: *.google.cl
  DNSName: *.google.co.in
  DNSName: *.google.co.jp
  DNSName: *.google.co.uk
  DNSName: *.google.com.ar
  DNSName: *.google.com.au
  DNSName: *.google.com.br
  DNSName: *.google.com.co
  DNSName: *.google.com.mx
  DNSName: *.google.com.tr
  DNSName: *.google.com.vn
  DNSName: *.google.de
  DNSName: *.google.es
  DNSName: *.google.fr
  DNSName: *.google.hu
  DNSName: *.google.it
  DNSName: *.google.nl
  DNSName: *.google.pl
  DNSName: *.google.pt
  DNSName: *.googleadapis.com
  DNSName: *.googleapis.cn
  DNSName: *.googlecommerce.com
  DNSName: *.googlevideo.com
  DNSName: *.gstatic.cn
  DNSName: *.gstatic.com
  DNSName: *.gstaticcnapps.cn
  DNSName: *.gvt1.com
  DNSName: *.gvt2.com
  DNSName: *.metric.gstatic.com
  DNSName: *.urchin.com
  DNSName: *.url.google.com
  DNSName: *.youtube-nocookie.com
  DNSName: *.youtube.com
  DNSName: *.youtubeeducation.com
  DNSName: *.youtubekids.com
  DNSName: *.yt.be
  DNSName: *.ytimg.com
  DNSName: android.clients.google.com
  DNSName: android.com
  DNSName: developer.android.google.cn
  DNSName: developers.android.google.cn
  DNSName: g.co
  DNSName: ggpht.cn
  DNSName: goo.gl
  DNSName: google-analytics.com
  DNSName: google.com
  DNSName: googlecommerce.com
  DNSName: source.android.google.cn
  DNSName: urchin.com
  DNSName: www.goo.gl
  DNSName: youtu.be
  DNSName: youtube.com
  DNSName: youtubeeducation.com
  DNSName: youtubekids.com
  DNSName: yt.be
]

#8: ObjectId: 2.5.29.14 Criticality=false
SubjectKeyIdentifier [
KeyIdentifier [
0000: BB F4 15 80 EC F0 4E F6   58 5A B1 49 4C 82 12 48  ......N.XZ.IL..H
0010: F9 FB 7E 3B                                        ...;
]
]

Step3. Check certificate in keystore

keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacerts
keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacerts | grep youtube

Step4. Specify trust store AND PASSWRD

-Djavax.net.ssl.trustStore=$JAVA_HOME/jre/lib/security/cacerts 
-Djavax.net.ssl.trustStorePassword=changeit 
-Djavax.net.debug=all

If there are some issue that hostname in certificate didn't matched, the steps below can help to confirm the issue.

  • Check the Server’s FQDN and make sure this match with the URL configured on the Certificate.
  • Wildcard certificate cannot support subdomain. The subdomain also need to create a certificate. How to Fix SSL Common Name Mismatch Error

2/14/2019

Ignore Certificate Verification Using RestTemplate

For some reasons, we don't want to verify certificate verification when data transfer has to happen over HTTPS.

How to disable verification using restTemplate in Spring?

  1. Custom trustStrategy that trusts all certs
  2. Implement hostname verification which trusts all host

1/17/2019

Show Java Settings as Default

Java -XshowSettings can show possible category arguments in JVM env.

-XshowSettings:category
Shows settings and continues. Possible category arguments for this option include the following:

all
Shows all categories of settings. This is the default value.

locale
Shows settings related to locale.

properties
Shows settings related to system properties.

vm
Shows the settings of the JVM.

java -XshowSettings:all -version

when executed above command, the usage information for running the Java launcher will also be displayed. It can make maintainer a bit less convenient to see those details.


VM settings:
    Max. Heap Size (Estimated): 3.56G
    Ergonomics Machine Class: server
    Using VM: Java HotSpot(TM) 64-Bit Server VM

Property settings:
    awt.toolkit = sun.lwawt.macosx.LWCToolkit
    file.encoding = UTF-8
    file.encoding.pkg = sun.io
    file.separator = /
    ftp.nonProxyHosts = local|*.local|169.254/16|*.169.254/16
    gopherProxySet = false
    http.nonProxyHosts = local|*.local|169.254/16|*.169.254/16
    java.awt.graphicsenv = sun.awt.CGraphicsEnvironment
    java.awt.printerjob = sun.lwawt.macosx.CPrinterJob
    java.class.path = .
    java.class.version = 52.0
    java.endorsed.dirs = /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/endorsed
    java.ext.dirs = /Users/chliu/Library/Java/Extensions
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext
        /Library/Java/Extensions
        /Network/Library/Java/Extensions
        /System/Library/Java/Extensions
        /usr/lib/java
    java.home = /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre
    java.io.tmpdir = /var/folders/zd/5kbv_wbd6cqbpfrf8w95sfnr0000gn/T/
    java.library.path = /Users/chliu/Library/Java/Extensions
        /Library/Java/Extensions
        /Network/Library/Java/Extensions
        /System/Library/Java/Extensions
        /usr/lib/java
        .
    java.runtime.name = Java(TM) SE Runtime Environment
    java.runtime.version = 1.8.0_111-b14
    java.specification.name = Java Platform API Specification
    java.specification.vendor = Oracle Corporation
    java.specification.version = 1.8
    java.vendor = Oracle Corporation
    java.vendor.url = http://java.oracle.com/
    java.vendor.url.bug = http://bugreport.sun.com/bugreport/
    java.version = 1.8.0_111
    java.vm.info = mixed mode
    java.vm.name = Java HotSpot(TM) 64-Bit Server VM
    java.vm.specification.name = Java Virtual Machine Specification
    java.vm.specification.vendor = Oracle Corporation
    java.vm.specification.version = 1.8
    java.vm.vendor = Oracle Corporation
    java.vm.version = 25.111-b14
    line.separator = \n
    os.arch = x86_64
    os.name = Mac OS X
    os.version = 10.14.2
    path.separator = :
    socksNonProxyHosts = local|*.local|169.254/16|*.169.254/16
    sun.arch.data.model = 64
    sun.boot.class.path = /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/resources.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/rt.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/sunrsasign.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jsse.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jce.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/charsets.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfr.jar
        /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/classes
    sun.boot.library.path = /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib
    sun.cpu.endian = little
    sun.cpu.isalist =
    sun.io.unicode.encoding = UnicodeBig
    sun.java.launcher = SUN_STANDARD
    sun.jnu.encoding = UTF-8
    sun.management.compiler = HotSpot 64-Bit Tiered Compilers
    sun.os.patch.level = unknown
    user.country = US
    user.country.format = TW
    user.dir = /Users/chliu/temp/aa/WEB-INF/lib
    user.home = /Users/chliu
    user.language = en
    user.name = chliu
    user.timezone =

Locale settings:
    default locale = English
    default display locale = English (United States)
    default format locale = English (Taiwan)
    available locales = , ar, ar_AE, ar_BH, ar_DZ, ar_EG, ar_IQ, ar_JO,
        ar_KW, ar_LB, ar_LY, ar_MA, ar_OM, ar_QA, ar_SA, ar_SD,
        ar_SY, ar_TN, ar_YE, be, be_BY, bg, bg_BG, ca,
        ca_ES, cs, cs_CZ, da, da_DK, de, de_AT, de_CH,
        de_DE, de_GR, de_LU, el, el_CY, el_GR, en, en_AU,
        en_CA, en_GB, en_IE, en_IN, en_MT, en_NZ, en_PH, en_SG,
        en_US, en_ZA, es, es_AR, es_BO, es_CL, es_CO, es_CR,
        es_CU, es_DO, es_EC, es_ES, es_GT, es_HN, es_MX, es_NI,
        es_PA, es_PE, es_PR, es_PY, es_SV, es_US, es_UY, es_VE,
        et, et_EE, fi, fi_FI, fr, fr_BE, fr_CA, fr_CH,
        fr_FR, fr_LU, ga, ga_IE, hi, hi_IN, hr, hr_HR,
        hu, hu_HU, in, in_ID, is, is_IS, it, it_CH,
        it_IT, iw, iw_IL, ja, ja_JP, ja_JP_JP_#u-ca-japanese, ko, ko_KR,
        lt, lt_LT, lv, lv_LV, mk, mk_MK, ms, ms_MY,
        mt, mt_MT, nl, nl_BE, nl_NL, no, no_NO, no_NO_NY,
        pl, pl_PL, pt, pt_BR, pt_PT, ro, ro_RO, ru,
        ru_RU, sk, sk_SK, sl, sl_SI, sq, sq_AL, sr,
        sr_BA, sr_BA_#Latn, sr_CS, sr_ME, sr_ME_#Latn, sr_RS, sr_RS_#Latn, sr__#Latn,
        sv, sv_SE, th, th_TH, th_TH_TH_#u-nu-thai, tr, tr_TR, uk,
        uk_UA, vi, vi_VN, zh, zh_CN, zh_HK, zh_SG, zh_TW

java version "1.8.0_111"
Java(TM) SE Runtime Environment (build 1.8.0_111-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.111-b14, mixed mode)

1/13/2019

[Java8] Method References

Method references are the special form of Lambda expression. Sometimes, however, a lambda expression does nothing but call an existing method. In those cases, this way is often clearer to refer to existing method by name. They are more compact and easy-to-ready to express something.

Basically, this is just shorthand syntax for a Lambda Expression but this version is more concise & readable.

Types of Method reference

There are four types of method reference.

Reference to a static method

  @Test
   public void testReferenceStaticMethod()
   {
      Function<String, String> upperFunc = StringUtils::toUpperCase;
      Assert.assertEquals("HI JAVA", upperFunc.apply("hi Java"));
   }

Reference to an instance method of a particular object

    @Test
   public void testInstanceMethod()
   {
      String text = "hi java";
      Supplier<Integer> getLength = text::length;
      Assert.assertEquals(Integer.valueOf(7), getLength.get());
   }

Reference to an instance method of a particular type

    @Test
   public void testInstanceMethodByType()
   {
      Function<String, String> upperFunc = String::toLowerCase;
      Assert.assertEquals("hi java", upperFunc.apply("hi Java"));
   }

Reference to a constructor

    @Test
    public void testCallConstructor()
   {
      Function<Integer, Integer> f = Integer::new;
      Assert.assertEquals(new Integer(99), f.apply(99));
   }

Conclusion

In conclusion, if possible, we should try to use method references can make our code cleaner, more readable & promote code reusability, but they have some restrictions on some cases.

1/07/2019

[Java8] the compiled bytecode of lambda

What's byecode of lambda be generated in Java is interesting for me. From below simple code, we can execute javap to get the compiled asm code which will be performed by JVM.

{
   private Function<String, Integer> f = s -> Integer.parseInt(s);
   public String test()
   {
      Function<String, String> c = (a) -> a.toUpperCase();
      Supplier<Date> s = () -> new Date();
      return c.apply("java") + s.get() + f.apply("99");
   }
}

javap -c -p LambdaBytecode.class

public class org.javasafari.lambda.LambdaBytecode {
  private java.util.function.Function<java.lang.String, java.lang.Integer> f;

  public org.javasafari.lambda.LambdaBytecode();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: aload_0
       5: invokedynamic #2,  0              // InvokeDynamic #0:apply:()Ljava/util/function/Function;
      10: putfield      #3                  // Field f:Ljava/util/function/Function;
      13: return

  public java.lang.String test();
    Code:
       0: invokedynamic #4,  0              // InvokeDynamic #1:apply:()Ljava/util/function/Function;
       5: astore_1
       6: invokedynamic #5,  0              // InvokeDynamic #2:get:()Ljava/util/function/Supplier;
      11: astore_2
      12: new           #6                  // class java/lang/StringBuilder
      15: dup
      16: invokespecial #7                  // Method java/lang/StringBuilder."<init>":()V
      19: aload_1
      20: ldc           #8                  // String java
      22: invokeinterface #9,  2            // InterfaceMethod java/util/function/Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
      27: checkcast     #10                 // class java/lang/String
      30: invokevirtual #11                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      33: aload_2
      34: invokeinterface #12,  1           // InterfaceMethod java/util/function/Supplier.get:()Ljava/lang/Object;
      39: invokevirtual #13                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
      42: aload_0
      43: getfield      #3                  // Field f:Ljava/util/function/Function;
      46: ldc           #14                 // String 99
      48: invokeinterface #9,  2            // InterfaceMethod java/util/function/Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
      53: invokevirtual #13                 // Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
      56: invokevirtual #15                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      59: areturn

  private static java.util.Date lambda$test$2();
    Code:
       0: new           #16                 // class java/util/Date
       3: dup
       4: invokespecial #17                 // Method java/util/Date."<init>":()V
       7: areturn

  private static java.lang.String lambda$test$1(java.lang.String);
    Code:
       0: aload_0
       1: invokevirtual #18                 // Method java/lang/String.toUpperCase:()Ljava/lang/String;
       4: areturn

  private static java.lang.Integer lambda$new$0(java.lang.String);
    Code:
       0: aload_0
       1: invokestatic  #19                 // Method java/lang/Integer.parseInt:(Ljava/lang/String;)I
       4: invokestatic  #20                 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
       7: areturn
}

Lambdas and invokedynamic

The translation of a lambda expression to be bytecode will be performed in below steps.

  • Generate an invokedynamic call site (lambda factory), which when invoked returns an instance of the Functional Interface defined.
  • Create a static method which included the lambda expression will be invoked through the invokedynamic instruction.

If you want to know how invokedynamic works, "Using Invoke Dynamic to Teach the JVM a New Language" is good for us.