├── .gitignore ├── .gradle ├── 5.2.1 │ ├── executionHistory │ │ ├── executionHistory.bin │ │ └── executionHistory.lock │ ├── fileChanges │ │ └── last-build.bin │ ├── fileHashes │ │ ├── fileHashes.bin │ │ └── fileHashes.lock │ └── gc.properties ├── buildOutputCleanup │ ├── buildOutputCleanup.lock │ ├── cache.properties │ └── outputFiles.bin └── vcs-1 │ └── gc.properties ├── .idea ├── codeStyles │ └── codeStyleConfig.xml ├── compiler.xml ├── gradle.xml ├── jarRepositories.xml ├── misc.xml ├── vcs.xml └── workspace.xml ├── LICENSE ├── README.md ├── build.gradle ├── gradle └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew ├── gradlew.bat ├── settings.gradle └── src └── main ├── java └── com │ └── gb │ └── didgen │ ├── BeanDefinition.java │ ├── DistributedIdDesignMain.java │ ├── IdGeneratorController.java │ ├── common │ └── Constants.java │ ├── exception │ ├── ClockMovedBackException.java │ └── NodeIdOutOfBoundException.java │ └── service │ ├── IdGenerator.java │ ├── SequenceIdGenerator.java │ ├── SnowflakeSequenceIdGenerator.java │ └── UUIDGenerator.java └── resources └── application.yml /.gitignore: -------------------------------------------------------------------------------- 1 | HELP.md 2 | .gradle 3 | build/ 4 | !gradle/wrapper/gradle-wrapper.jar 5 | !**/src/main/** 6 | !**/src/test/** 7 | 8 | ### STS ### 9 | .apt_generated 10 | .classpath 11 | .factorypath 12 | .project 13 | .settings 14 | .springBeans 15 | .sts4-cache 16 | 17 | ### IntelliJ IDEA ### 18 | .idea 19 | *.iws 20 | *.iml 21 | *.ipr 22 | out/ 23 | 24 | ### NetBeans ### 25 | /nbproject/private/ 26 | /nbbuild/ 27 | /dist/ 28 | /nbdist/ 29 | /.nb-gradle/ 30 | 31 | ### VS Code ### 32 | .vscode/ 33 | -------------------------------------------------------------------------------- /.gradle/5.2.1/executionHistory/executionHistory.bin: -------------------------------------------------------------------------------- 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file://$PROJECT_DIR$/src/main/java/com/gb/didgen/service/SnowflakeSequenceIdGenerator.java 294 | 36 295 | 297 | 298 | file://$PROJECT_DIR$/src/main/java/com/gb/didgen/IdGeneratorController.java 299 | 17 300 | 302 | 303 | 304 | 305 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright [yyyy] [name of copyright owner] 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Distributed Id Generation 2 | 3 | What is the need to generate a unique identifier? 4 | 5 | We as part of day to day operation do capture occurrences of events and persist them in data stores. Each of these entries has to be identified uniquely. This is where we use identifiers to identify them. The identifiers that are used to identify the record uniquely may be of numeric type or string type. 6 | 7 | The requirement is to create ids which is roughly sorted by time and can be used across products i.e the same id generator should be used across domains. Consider a retail example the same id generator should be used for order, stock, price, payment, shipment, notification etc. The id generation should be fast and should generate unique and should not have single point of failures. 8 | 9 | In this tutorial we are going to look in to ways to create these identifiers in different use cases. 10 | 11 | 1. Create id in database. 12 | 2. Create id from backend and send to database. 13 | 14 | ## UUIDs 15 | 16 | UUID - universally unique id or GUID by microsoft is a 128 bit id used to generate ids which can be generated in distributed manner and still remain unique. This uniqueness does not depend on central co-ordination between the systems creating them. So the defacto choice for many people creating unique identifiers are UUIDs. The possibility of duplication even when created in distributed manner is close to zero. Since the possible values are 2 to the power of 128 the max values is 340,​282,​366,​920,​938,​463,​463,​374,​607,​431,​768,​211,​456. 17 | 18 | Sample UUID - xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx 19 | 907f39b0-6778-**4**c47-b173-e6348efa1641 20 | M is the UUID version here we are using type 4 UUIDs 21 | N is the UUID variant 22 | 23 | The default UUIDs that we create out of syntax. 24 | ``` 25 | UUID.randomUUID() is version 4 UUID 26 | ``` 27 | 28 | What are the pros and cons of UUIDs to uniquely identify records? 29 | 30 | Easy to generate. 31 | Fast. 32 | Uniquness. 33 | Random i.e. we cannot predict next id with the current id. 34 | 35 | UUIDs are 128 bits long which is 32 chars in length. 36 | Sorting UUIDs would not result in ordering of actual records since they are random and not generated in any sequence. 37 | 38 | ## Auto incrementing Ids - Identity columns 39 | 40 | We can use identity columns as key to generate ids for records and this will work for most of the use cases where the uniqueness is for a particular type but when we move across types or entities this approach cannot be used as it is restricted to a table. 41 | 42 | ## Understanding the requirements again with examples 43 | 44 | Consider capturing of occurrences in distributed systems may be take an example of online shopping systems. Item added to cart where the cart with an id. Check out will have an id, payment will have an id and shipment will have an id and delivery notification with an id. It would be easy for someone who monitors the system to track these since the events will have identifiers which having identifiers in increasing order and gives a clear indication that payment event occurred after order event. 45 | 46 | One more example that we can think of is - Social networking site where user creates a post with a unique id. These posts attract likes, comments from users or people who subscribed to certain types of events. In this it would be useful to understand and trace a like or comment to a post will always have an identifier which is greater than the post itself. 47 | 48 | ## Centralized Id generation 49 | 50 | We can have a service that can generate identifiers and distribute them to services. We need to handle concurrency and synchoronization. Consider the scale at which requests come for Twitter, Flickr, sale day in Amazon or Flipkart. We expect on an average of 10000 requests per second and having a centralized service to handle requests at this scale is not easy and any failure will have impact on the platform. 51 | 52 | ## Id generation based on Twitter snowflake algorithm will help here. 53 | 54 | https://blog.twitter.com/engineering/en_us/a/2010/announcing-snowflake.html 55 | 56 | Other references 57 | https://github.com/sony/sonyflake 58 | https://instagram-engineering.com/sharding-ids-at-instagram-1cf5a71e5a5c 59 | https://docs.mongodb.com/manual/reference/method/ObjectId/ 60 | 61 | -------------------------------------------------------------------------------- /build.gradle: -------------------------------------------------------------------------------- 1 | plugins { 2 | id 'org.springframework.boot' version '2.2.6.RELEASE' 3 | id 'io.spring.dependency-management' version '1.0.9.RELEASE' 4 | id 'java' 5 | } 6 | 7 | group 'com.gb.didgen' 8 | version '1.0-SNAPSHOT' 9 | 10 | sourceCompatibility = 1.8 11 | 12 | repositories { 13 | mavenCentral() 14 | jcenter() 15 | } 16 | 17 | dependencies { 18 | compile 'org.springframework.boot:spring-boot-starter-web' 19 | compile group: 'org.apache.commons', name: 'commons-lang3', version: '3.10' 20 | compile('com.fasterxml.jackson.datatype:jackson-datatype-jsr310') 21 | compileOnly 'org.projectlombok:lombok:1.18.12' 22 | compile group: 'org.apache.commons', name: 'commons-lang3', version: '3.10' 23 | annotationProcessor 'org.projectlombok:lombok:1.18.12' 24 | testImplementation 'org.junit.jupiter:junit-jupiter-api:5.3.1' 25 | testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.3.1' 26 | // https://mvnrepository.com/artifact/org.mockito/mockito-junit-jupiter 27 | testCompile group: 'org.mockito', name: 'mockito-junit-jupiter', version: '3.3.3' 28 | } 29 | test { 30 | useJUnitPlatform() 31 | } -------------------------------------------------------------------------------- /gradle/wrapper/gradle-wrapper.jar: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/gopalbala/distributed-idgen/9100eb3b9dfeaf36fdc64d34cff207cdad22464a/gradle/wrapper/gradle-wrapper.jar -------------------------------------------------------------------------------- /gradle/wrapper/gradle-wrapper.properties: -------------------------------------------------------------------------------- 1 | #Sat Jul 04 20:51:43 IST 2020 2 | distributionUrl=https\://services.gradle.org/distributions/gradle-5.2.1-all.zip 3 | distributionBase=GRADLE_USER_HOME 4 | distributionPath=wrapper/dists 5 | zipStorePath=wrapper/dists 6 | zipStoreBase=GRADLE_USER_HOME 7 | -------------------------------------------------------------------------------- /gradlew: -------------------------------------------------------------------------------- 1 | #!/usr/bin/env sh 2 | 3 | ############################################################################## 4 | ## 5 | ## Gradle start up script for UN*X 6 | ## 7 | ############################################################################## 8 | 9 | # Attempt to set APP_HOME 10 | # Resolve links: $0 may be a link 11 | PRG="$0" 12 | # Need this for relative symlinks. 13 | while [ -h "$PRG" ] ; do 14 | ls=`ls -ld "$PRG"` 15 | link=`expr "$ls" : '.*-> \(.*\)$'` 16 | if expr "$link" : '/.*' > /dev/null; then 17 | PRG="$link" 18 | else 19 | PRG=`dirname "$PRG"`"/$link" 20 | fi 21 | done 22 | SAVED="`pwd`" 23 | cd "`dirname \"$PRG\"`/" >/dev/null 24 | APP_HOME="`pwd -P`" 25 | cd "$SAVED" >/dev/null 26 | 27 | APP_NAME="Gradle" 28 | APP_BASE_NAME=`basename "$0"` 29 | 30 | # Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script. 31 | DEFAULT_JVM_OPTS='"-Xmx64m"' 32 | 33 | # Use the maximum available, or set MAX_FD != -1 to use that value. 34 | MAX_FD="maximum" 35 | 36 | warn () { 37 | echo "$*" 38 | } 39 | 40 | die () { 41 | echo 42 | echo "$*" 43 | echo 44 | exit 1 45 | } 46 | 47 | # OS specific support (must be 'true' or 'false'). 48 | cygwin=false 49 | msys=false 50 | darwin=false 51 | nonstop=false 52 | case "`uname`" in 53 | CYGWIN* ) 54 | cygwin=true 55 | ;; 56 | Darwin* ) 57 | darwin=true 58 | ;; 59 | MINGW* ) 60 | msys=true 61 | ;; 62 | NONSTOP* ) 63 | nonstop=true 64 | ;; 65 | esac 66 | 67 | CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar 68 | 69 | # Determine the Java command to use to start the JVM. 70 | if [ -n "$JAVA_HOME" ] ; then 71 | if [ -x "$JAVA_HOME/jre/sh/java" ] ; then 72 | # IBM's JDK on AIX uses strange locations for the executables 73 | JAVACMD="$JAVA_HOME/jre/sh/java" 74 | else 75 | JAVACMD="$JAVA_HOME/bin/java" 76 | fi 77 | if [ ! -x "$JAVACMD" ] ; then 78 | die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME 79 | 80 | Please set the JAVA_HOME variable in your environment to match the 81 | location of your Java installation." 82 | fi 83 | else 84 | JAVACMD="java" 85 | which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 86 | 87 | Please set the JAVA_HOME variable in your environment to match the 88 | location of your Java installation." 89 | fi 90 | 91 | # Increase the maximum file descriptors if we can. 92 | if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then 93 | MAX_FD_LIMIT=`ulimit -H -n` 94 | if [ $? -eq 0 ] ; then 95 | if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then 96 | MAX_FD="$MAX_FD_LIMIT" 97 | fi 98 | ulimit -n $MAX_FD 99 | if [ $? -ne 0 ] ; then 100 | warn "Could not set maximum file descriptor limit: $MAX_FD" 101 | fi 102 | else 103 | warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT" 104 | fi 105 | fi 106 | 107 | # For Darwin, add options to specify how the application appears in the dock 108 | if $darwin; then 109 | GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\"" 110 | fi 111 | 112 | # For Cygwin, switch paths to Windows format before running java 113 | if $cygwin ; then 114 | APP_HOME=`cygpath --path --mixed "$APP_HOME"` 115 | CLASSPATH=`cygpath --path --mixed "$CLASSPATH"` 116 | JAVACMD=`cygpath --unix "$JAVACMD"` 117 | 118 | # We build the pattern for arguments to be converted via cygpath 119 | ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null` 120 | SEP="" 121 | for dir in $ROOTDIRSRAW ; do 122 | ROOTDIRS="$ROOTDIRS$SEP$dir" 123 | SEP="|" 124 | done 125 | OURCYGPATTERN="(^($ROOTDIRS))" 126 | # Add a user-defined pattern to the cygpath arguments 127 | if [ "$GRADLE_CYGPATTERN" != "" ] ; then 128 | OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)" 129 | fi 130 | # Now convert the arguments - kludge to limit ourselves to /bin/sh 131 | i=0 132 | for arg in "$@" ; do 133 | CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -` 134 | CHECK2=`echo "$arg"|egrep -c "^-"` ### Determine if an option 135 | 136 | if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then ### Added a condition 137 | eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"` 138 | else 139 | eval `echo args$i`="\"$arg\"" 140 | fi 141 | i=$((i+1)) 142 | done 143 | case $i in 144 | (0) set -- ;; 145 | (1) set -- "$args0" ;; 146 | (2) set -- "$args0" "$args1" ;; 147 | (3) set -- "$args0" "$args1" "$args2" ;; 148 | (4) set -- "$args0" "$args1" "$args2" "$args3" ;; 149 | (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;; 150 | (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;; 151 | (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;; 152 | (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;; 153 | (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;; 154 | esac 155 | fi 156 | 157 | # Escape application args 158 | save () { 159 | for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done 160 | echo " " 161 | } 162 | APP_ARGS=$(save "$@") 163 | 164 | # Collect all arguments for the java command, following the shell quoting and substitution rules 165 | eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS" 166 | 167 | # by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong 168 | if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then 169 | cd "$(dirname "$0")" 170 | fi 171 | 172 | exec "$JAVACMD" "$@" 173 | -------------------------------------------------------------------------------- /gradlew.bat: -------------------------------------------------------------------------------- 1 | @if "%DEBUG%" == "" @echo off 2 | @rem ########################################################################## 3 | @rem 4 | @rem Gradle startup script for Windows 5 | @rem 6 | @rem ########################################################################## 7 | 8 | @rem Set local scope for the variables with windows NT shell 9 | if "%OS%"=="Windows_NT" setlocal 10 | 11 | set DIRNAME=%~dp0 12 | if "%DIRNAME%" == "" set DIRNAME=. 13 | set APP_BASE_NAME=%~n0 14 | set APP_HOME=%DIRNAME% 15 | 16 | @rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script. 17 | set DEFAULT_JVM_OPTS="-Xmx64m" 18 | 19 | @rem Find java.exe 20 | if defined JAVA_HOME goto findJavaFromJavaHome 21 | 22 | set JAVA_EXE=java.exe 23 | %JAVA_EXE% -version >NUL 2>&1 24 | if "%ERRORLEVEL%" == "0" goto init 25 | 26 | echo. 27 | echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 28 | echo. 29 | echo Please set the JAVA_HOME variable in your environment to match the 30 | echo location of your Java installation. 31 | 32 | goto fail 33 | 34 | :findJavaFromJavaHome 35 | set JAVA_HOME=%JAVA_HOME:"=% 36 | set JAVA_EXE=%JAVA_HOME%/bin/java.exe 37 | 38 | if exist "%JAVA_EXE%" goto init 39 | 40 | echo. 41 | echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 42 | echo. 43 | echo Please set the JAVA_HOME variable in your environment to match the 44 | echo location of your Java installation. 45 | 46 | goto fail 47 | 48 | :init 49 | @rem Get command-line arguments, handling Windows variants 50 | 51 | if not "%OS%" == "Windows_NT" goto win9xME_args 52 | 53 | :win9xME_args 54 | @rem Slurp the command line arguments. 55 | set CMD_LINE_ARGS= 56 | set _SKIP=2 57 | 58 | :win9xME_args_slurp 59 | if "x%~1" == "x" goto execute 60 | 61 | set CMD_LINE_ARGS=%* 62 | 63 | :execute 64 | @rem Setup the command line 65 | 66 | set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar 67 | 68 | @rem Execute Gradle 69 | "%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS% 70 | 71 | :end 72 | @rem End local scope for the variables with windows NT shell 73 | if "%ERRORLEVEL%"=="0" goto mainEnd 74 | 75 | :fail 76 | rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of 77 | rem the _cmd.exe /c_ return code! 78 | if not "" == "%GRADLE_EXIT_CONSOLE%" exit 1 79 | exit /b 1 80 | 81 | :mainEnd 82 | if "%OS%"=="Windows_NT" endlocal 83 | 84 | :omega 85 | -------------------------------------------------------------------------------- /settings.gradle: -------------------------------------------------------------------------------- 1 | rootProject.name = 'distributed-idgen' 2 | 3 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/BeanDefinition.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen; 2 | 3 | import org.springframework.context.annotation.Bean; 4 | import org.springframework.stereotype.Component; 5 | 6 | import java.net.NetworkInterface; 7 | import java.net.SocketException; 8 | import java.security.SecureRandom; 9 | import java.util.Enumeration; 10 | 11 | import static com.gb.didgen.common.Constants.NODE_ID_BIT_LEN; 12 | 13 | @Component 14 | public class BeanDefinition { 15 | @Bean 16 | public Integer generatingNodeId() { 17 | int maxNodeVal = (int) Math.pow(2, NODE_ID_BIT_LEN); 18 | int nodeId; 19 | try { 20 | StringBuilder sb = new StringBuilder(); 21 | Enumeration networkInterfaces = NetworkInterface.getNetworkInterfaces(); 22 | while (networkInterfaces.hasMoreElements()) { 23 | NetworkInterface networkInterface = networkInterfaces.nextElement(); 24 | byte[] mac = networkInterface.getHardwareAddress(); 25 | if (mac != null) { 26 | for (int i = 0; i < mac.length; i++) { 27 | sb.append(String.format("%02X", mac[i])); 28 | } 29 | } 30 | } 31 | nodeId = sb.toString().hashCode(); 32 | } catch (SocketException ex) { 33 | //in case of exception get a random number limited by max node size 34 | nodeId = (int) (new SecureRandom().nextInt() % Math.pow(2, 10)); 35 | } 36 | nodeId = nodeId & maxNodeVal; 37 | return nodeId; 38 | } 39 | } 40 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/DistributedIdDesignMain.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen; 2 | 3 | import org.springframework.boot.SpringApplication; 4 | import org.springframework.boot.autoconfigure.SpringBootApplication; 5 | 6 | @SpringBootApplication 7 | public class DistributedIdDesignMain { 8 | public static void main(String[] args) { 9 | SpringApplication.run(DistributedIdDesignMain.class); 10 | } 11 | } 12 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/IdGeneratorController.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen; 2 | 3 | import com.gb.didgen.exception.ClockMovedBackException; 4 | import com.gb.didgen.exception.NodeIdOutOfBoundException; 5 | import com.gb.didgen.service.SequenceIdGenerator; 6 | import org.springframework.beans.factory.annotation.Autowired; 7 | import org.springframework.http.ResponseEntity; 8 | import org.springframework.web.bind.annotation.GetMapping; 9 | import org.springframework.web.bind.annotation.RestController; 10 | 11 | @RestController() 12 | public class IdGeneratorController { 13 | @Autowired 14 | private SequenceIdGenerator sequenceIdGenerator; 15 | 16 | @GetMapping(produces = {"application/JSON"}) 17 | public ResponseEntity getNextId() throws NodeIdOutOfBoundException, ClockMovedBackException { 18 | return ResponseEntity.ok(sequenceIdGenerator.generateId()); 19 | } 20 | } 21 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/common/Constants.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.common; 2 | 3 | public class Constants { 4 | public static final int SIGN_BIT_LEN = 1; 5 | public static final int EPOCH_BIT_LEN = 41; 6 | public static final int NODE_ID_BIT_LEN = 10; 7 | public static final int SEQUENCE_BIT_LEN = 12; 8 | } 9 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/exception/ClockMovedBackException.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.exception; 2 | 3 | public class ClockMovedBackException extends Exception { 4 | public ClockMovedBackException(String message) { 5 | super(message); 6 | } 7 | } 8 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/exception/NodeIdOutOfBoundException.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.exception; 2 | 3 | public class NodeIdOutOfBoundException extends Exception { 4 | public NodeIdOutOfBoundException(String message) { 5 | super(message); 6 | } 7 | } 8 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/service/IdGenerator.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.service; 2 | 3 | public interface IdGenerator { 4 | String generateId(); 5 | } 6 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/service/SequenceIdGenerator.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.service; 2 | 3 | import com.gb.didgen.exception.ClockMovedBackException; 4 | import com.gb.didgen.exception.NodeIdOutOfBoundException; 5 | import org.springframework.stereotype.Service; 6 | 7 | @Service 8 | public interface SequenceIdGenerator { 9 | long generateId() throws ClockMovedBackException, NodeIdOutOfBoundException; 10 | } 11 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/service/SnowflakeSequenceIdGenerator.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.service; 2 | 3 | import com.gb.didgen.exception.ClockMovedBackException; 4 | import com.gb.didgen.exception.NodeIdOutOfBoundException; 5 | import org.springframework.beans.factory.annotation.Autowired; 6 | import org.springframework.stereotype.Service; 7 | 8 | import javax.annotation.PostConstruct; 9 | import java.time.Instant; 10 | 11 | import static com.gb.didgen.common.Constants.NODE_ID_BIT_LEN; 12 | import static com.gb.didgen.common.Constants.SEQUENCE_BIT_LEN; 13 | 14 | @Service 15 | public class SnowflakeSequenceIdGenerator implements SequenceIdGenerator { 16 | @Autowired 17 | private Integer generatingNodeId; 18 | 19 | private final int maxSequence = (int) Math.pow(2, SEQUENCE_BIT_LEN); 20 | private final int maxNodeVal = (int) Math.pow(2, NODE_ID_BIT_LEN); 21 | private final long EPOCH_START = Instant.EPOCH.toEpochMilli(); 22 | 23 | 24 | private volatile long currentSequence = -1L; 25 | private final Object lock = new Object(); 26 | private volatile long lastTimestamp = -1L; 27 | 28 | @PostConstruct 29 | public void checkNodeIdBounds() throws NodeIdOutOfBoundException { 30 | if (generatingNodeId < 0 || generatingNodeId > maxNodeVal) { 31 | throw new NodeIdOutOfBoundException("Node id is < 0 or > " + maxNodeVal); 32 | } 33 | } 34 | 35 | @Override 36 | public long generateId() throws ClockMovedBackException, NodeIdOutOfBoundException { 37 | checkNodeIdBounds(); 38 | synchronized (lock) { 39 | long currentTimeStamp = getTimeStamp(); 40 | if (currentTimeStamp < lastTimestamp) { 41 | throw new ClockMovedBackException("Clock moved back"); 42 | } 43 | if (currentTimeStamp == lastTimestamp) { 44 | currentSequence = currentSequence + 1 & maxSequence; 45 | if (currentSequence != 0) { 46 | currentTimeStamp = waitNextMillis(currentTimeStamp); 47 | } 48 | } else { 49 | currentSequence = 0; 50 | } 51 | lastTimestamp = currentTimeStamp; 52 | long id = currentTimeStamp << (NODE_ID_BIT_LEN + SEQUENCE_BIT_LEN); 53 | id |= (generatingNodeId << SEQUENCE_BIT_LEN); 54 | id |= currentSequence; 55 | return id; 56 | } 57 | } 58 | 59 | private long getTimeStamp() { 60 | return Instant.now().toEpochMilli() - EPOCH_START; 61 | } 62 | 63 | private long waitNextMillis(long currentTimeStamp) { 64 | while (currentTimeStamp == lastTimestamp) { 65 | currentTimeStamp = getTimeStamp(); 66 | } 67 | return currentTimeStamp; 68 | } 69 | } 70 | -------------------------------------------------------------------------------- /src/main/java/com/gb/didgen/service/UUIDGenerator.java: -------------------------------------------------------------------------------- 1 | package com.gb.didgen.service; 2 | 3 | import java.util.UUID; 4 | 5 | public class UUIDGenerator implements IdGenerator { 6 | @Override 7 | public String generateId() { 8 | return UUID.randomUUID().toString(); 9 | } 10 | } 11 | -------------------------------------------------------------------------------- /src/main/resources/application.yml: -------------------------------------------------------------------------------- 1 | server: 2 | port: 8090 --------------------------------------------------------------------------------