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NOTE

Spring Boot Jar Startup Principle

1. Experiment. 2. Structure of an executable Jar. 3. How the program entry point is found. 4. Jar packages that can start without the java -jar command. 5. Reference.

JavaCreated Updated 1 min readhistorical

This is a historical learning note and may contain outdated or incomplete understanding.

1. Experiment

  • pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zsk.test</groupId>
    <artifactId>test</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.20.RELEASE</version>
    </parent>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.6</version>
        </dependency>
        <!-- aop -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <!--test-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>1.5.20.RELEASE</version>
            </plugin>
        </plugins>
    </build>
</project>
  • com.zsk.test.Application
package com.zsk.test;

import com.zsk.test.controller.TestController;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cache.annotation.EnableCaching;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.scheduling.annotation.EnableAsync;

/**
 * @description:
 * @author: zsk
 * @create: 2019-11-26 22:59
 **/
@EnableCaching
@EnableAsync
@SpringBootApplication()
public class Application
{
    public static void main(String[] args)
    {
        ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
        System.out.println("==================================Service started==================================");
        TestController bean = context.getBean(TestController.class);
        bean.test();

    }
}
  • Build the jar package.
mvn clean package -Dmaven.test.skip=true
  • After extracting it, use the tree command to inspect the structure.
C:.
├─BOOT-INF
│  ├─classes
│  │  └─com
│  │      └─zsk
│  │          └─test
│  │              ├─bean
│  │              ├─config
│  │              │  └─event
│  │              ├─controller
│  │              └─service
│  └─lib
├─META-INF
│  └─maven
│      └─com.zsk.test
│          └─test
└─org
    └─springframework
        └─boot
            └─loader
                ├─archive
                ├─data
                ├─jar
                └─util

2. Structure of an Executable Jar

  • Contains:
    • Jar description: META-INF/MANIFEST.MF
    • Spring Boot Loader: org/springframework/boot/loader
    • Project content: BOOT-INF/classes
    • Project dependencies: BOOT-INF/lib
  • Does not contain:
    • JDK
    • JRE

3. How to Find the Program Entry Point

Manifest-Version: 1.0
Implementation-Title: test
Implementation-Version: 1.0-SNAPSHOT
Archiver-Version: Plexus Archiver
Built-By: zsk
Implementation-Vendor-Id: com.zsk.test
Spring-Boot-Version: 1.5.20.RELEASE
Implementation-Vendor: Pivotal Software, Inc.
Main-Class: org.springframework.boot.loader.JarLauncher
Start-Class: com.zsk.test.Application
Spring-Boot-Classes: BOOT-INF/classes/
Spring-Boot-Lib: BOOT-INF/lib/
Created-By: Apache Maven 3.6.2
Build-Jdk: 1.8.0_231
Implementation-URL: https://projects.spring.io/spring-boot/test/
  1. META-INF/MANIFEST.MF specifies the startup class of the Jar, namely Main-Class: org.springframework.boot.loader.JarLauncher.
  2. META-INF/MANIFEST.MF specifies the main class of the project, namely Start-Class: the class annotated with @SpringBootApplication.

4. Jar Packages That Can Start Without the java -jar Command

  • pom.xml
<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>1.5.20.RELEASE</version>
                <configuration>
                    <executable>true</executable>
                </configuration>
            </plugin>
        </plugins>
    </build>
  • Custom configuration is supported.

Create a file with the same name and a .conf extension in the same directory.

  • test.conf
JAVA_OPTS="Xmx1024m -Xms1024m -Xmn384m"
  • Use jinfo -flags PID to inspect JVM arguments.

4.1. Principle

  • Use head -n 280 <jar-file> to inspect it. You can see that it is a bat file.
#!/bin/bash
#
#    .   ____          _            __ _ _
#   /\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
#  ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
#   \/  ___)| |_)| | | | | || (_| |  ) ) ) )
#    '  |____| .__|_| |_|_| |_\__, | / / / /
#   =========|_|==============|___/=/_/_/_/
#   :: Spring Boot Startup Script ::
#

### BEGIN INIT INFO
# Provides:          test
# Required-Start:    $remote_fs $syslog $network
# Required-Stop:     $remote_fs $syslog $network
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: test
# Description:       Parent pom providing dependency and plugin management for applications built with Maven
# chkconfig:         2345 99 01
### END INIT INFO

[[ -n "$DEBUG" ]] && set -x

# Initialize variables that cannot be provided by a .conf file
WORKING_DIR="$(pwd)"
# shellcheck disable=SC2153
[[ -n "$JARFILE" ]] && jarfile="$JARFILE"
[[ -n "$APP_NAME" ]] && identity="$APP_NAME"

# Follow symlinks to find the real jar and detect init.d script
cd "$(dirname "$0")" || exit 1
[[ -z "$jarfile" ]] && jarfile=$(pwd)/$(basename "$0")
while [[ -L "$jarfile" ]]; do
  [[ "$jarfile" =~ init\.d ]] && init_script=$(basename "$jarfile")
  jarfile=$(readlink "$jarfile")
  cd "$(dirname "$jarfile")" || exit 1
  jarfile=$(pwd)/$(basename "$jarfile")
done
jarfolder="$( (cd "$(dirname "$jarfile")" && pwd -P) )"
cd "$WORKING_DIR" || exit 1

# Source any config file
configfile="$(basename "${jarfile%.*}.conf")"

# Initialize CONF_FOLDER location defaulting to jarfolder
[[ -z "$CONF_FOLDER" ]] && CONF_FOLDER="${jarfolder}"

# shellcheck source=/dev/null
[[ -r "${CONF_FOLDER}/${configfile}" ]] && source "${CONF_FOLDER}/${configfile}"

# Initialize PID/LOG locations if they weren't provided by the config file
[[ -z "$PID_FOLDER" ]] && PID_FOLDER="/var/run"
[[ -z "$LOG_FOLDER" ]] && LOG_FOLDER="/var/log"
! [[ "$PID_FOLDER" == /* ]] && PID_FOLDER="$(dirname "$jarfile")"/"$PID_FOLDER"
! [[ "$LOG_FOLDER" == /* ]] && LOG_FOLDER="$(dirname "$jarfile")"/"$LOG_FOLDER"
! [[ -x "$PID_FOLDER" ]] && PID_FOLDER="/tmp"
! [[ -x "$LOG_FOLDER" ]] && LOG_FOLDER="/tmp"

# Set up defaults
[[ -z "$MODE" ]] && MODE="auto" # modes are "auto", "service" or "run"
[[ -z "$USE_START_STOP_DAEMON" ]] && USE_START_STOP_DAEMON="true"

# Create an identity for log/pid files
if [[ -z "$identity" ]]; then
  if [[ -n "$init_script" ]]; then
    identity="${init_script}"
  else
    identity=$(basename "${jarfile%.*}")_${jarfolder//\//}
  fi
fi

# Initialize log file name if not provided by the config file
[[ -z "$LOG_FILENAME" ]] && LOG_FILENAME="${identity}.log"

# Initialize stop wait time if not provided by the config file
[[ -z "$STOP_WAIT_TIME" ]] && STOP_WAIT_TIME="60"

# ANSI Colors
echoRed() { echo $'\e[0;31m'"$1"$'\e[0m'; }
echoGreen() { echo $'\e[0;32m'"$1"$'\e[0m'; }
echoYellow() { echo $'\e[0;33m'"$1"$'\e[0m'; }

# Utility functions
checkPermissions() {
  touch "$pid_file" &> /dev/null || { echoRed "Operation not permitted (cannot access pid file)"; return 4; }
  touch "$log_file" &> /dev/null || { echoRed "Operation not permitted (cannot access log file)"; return 4; }
}

isRunning() {
  ps -p "$1" &> /dev/null
}

await_file() {
  end=$(date +%s)
  let "end+=10"
  while [[ ! -s "$1" ]]
  do
    now=$(date +%s)
    if [[ $now -ge $end ]]; then
      break
    fi
    sleep 1
  done
}

# Determine the script mode
action="run"
if [[ "$MODE" == "auto" && -n "$init_script" ]] || [[ "$MODE" == "service" ]]; then
  action="$1"
  shift
fi

# Build the pid and log filenames
PID_FOLDER="$PID_FOLDER/${identity}"
pid_file="$PID_FOLDER/${identity}.pid"
log_file="$LOG_FOLDER/$LOG_FILENAME"

# Determine the user to run as if we are root
# shellcheck disable=SC2012
[[ $(id -u) == "0" ]] && run_user=$(ls -ld "$jarfile" | awk '{print $3}')

# Find Java
if [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]]; then
    javaexe="$JAVA_HOME/bin/java"
elif type -p java > /dev/null 2>&1; then
    javaexe=$(type -p java)
elif [[ -x "/usr/bin/java" ]];  then
    javaexe="/usr/bin/java"
else
    echo "Unable to find Java"
    exit 1
fi

arguments=(-Dsun.misc.URLClassPath.disableJarChecking=true $JAVA_OPTS -jar "$jarfile" $RUN_ARGS "$@")

# Action functions
start() {
  if [[ -f "$pid_file" ]]; then
    pid=$(cat "$pid_file")
    isRunning "$pid" && { echoYellow "Already running [$pid]"; return 0; }
  fi
  do_start "$@"
}

do_start() {
  working_dir=$(dirname "$jarfile")
  pushd "$working_dir" > /dev/null
  if [[ ! -e "$PID_FOLDER" ]]; then
    mkdir -p "$PID_FOLDER" &> /dev/null
    if [[ -n "$run_user" ]]; then
      chown "$run_user" "$PID_FOLDER"
    fi
  fi
  if [[ ! -e "$log_file" ]]; then
    touch "$log_file" &> /dev/null
    if [[ -n "$run_user" ]]; then
      chown "$run_user" "$log_file"
    fi
  fi
  if [[ -n "$run_user" ]]; then
    checkPermissions || return $?
    if [ $USE_START_STOP_DAEMON = true ] && type start-stop-daemon > /dev/null 2>&1; then
      start-stop-daemon --start --quiet \
        --chuid "$run_user" \
        --name "$identity" \
        --make-pidfile --pidfile "$pid_file" \
        --background --no-close \
        --startas "$javaexe" \
        --chdir "$working_dir" \
        -- "${arguments[@]}" \
        >> "$log_file" 2>&1
      await_file "$pid_file"
    else
      su -s /bin/sh -c "$javaexe $(printf "\"%s\" " "${arguments[@]}") >> \"$log_file\" 2>&1 & echo \$!" "$run_user" > "$pid_file"
    fi
    pid=$(cat "$pid_file")
  else
    checkPermissions || return $?
    "$javaexe" "${arguments[@]}" >> "$log_file" 2>&1 &
    pid=$!
    disown $pid
    echo "$pid" > "$pid_file"
  fi
  [[ -z $pid ]] && { echoRed "Failed to start"; return 1; }
  echoGreen "Started [$pid]"
}

stop() {
  working_dir=$(dirname "$jarfile")
  pushd "$working_dir" > /dev/null
  [[ -f $pid_file ]] || { echoYellow "Not running (pidfile not found)"; return 0; }
  pid=$(cat "$pid_file")
  isRunning "$pid" || { echoYellow "Not running (process ${pid}). Removing stale pid file."; rm -f "$pid_file"; return 0; }
  do_stop "$pid" "$pid_file"
}

do_stop() {
  kill "$1" &> /dev/null || { echoRed "Unable to kill process $1"; return 1; }
  for i in $(seq 1 $STOP_WAIT_TIME); do
    isRunning "$1" || { echoGreen "Stopped [$1]"; rm -f "$2"; return 0; }
    [[ $i -eq STOP_WAIT_TIME/2 ]] && kill "$1" &> /dev/null
    sleep 1
  done
  echoRed "Unable to kill process $1";
  return 1;
}

force_stop() {
  [[ -f $pid_file ]] || { echoYellow "Not running (pidfile not found)"; return 0; }
  pid=$(cat "$pid_file")
  isRunning "$pid" || { echoYellow "Not running (process ${pid}). Removing stale pid file."; rm -f "$pid_file"; return 0; }
  do_force_stop "$pid" "$pid_file"
}

do_force_stop() {
  kill -9 "$1" &> /dev/null || { echoRed "Unable to kill process $1"; return 1; }
  for i in $(seq 1 $STOP_WAIT_TIME); do
    isRunning "$1" || { echoGreen "Stopped [$1]"; rm -f "$2"; return 0; }
    [[ $i -eq STOP_WAIT_TIME/2 ]] && kill -9 "$1" &> /dev/null
    sleep 1
  done
  echoRed "Unable to kill process $1";
  return 1;
}

restart() {
  stop && start
}

force_reload() {
  working_dir=$(dirname "$jarfile")
  pushd "$working_dir" > /dev/null
  [[ -f $pid_file ]] || { echoRed "Not running (pidfile not found)"; return 7; }
  pid=$(cat "$pid_file")
  rm -f "$pid_file"
  isRunning "$pid" || { echoRed "Not running (process ${pid} not found)"; return 7; }
  do_stop "$pid" "$pid_file"
  do_start
}

status() {
  working_dir=$(dirname "$jarfile")
  pushd "$working_dir" > /dev/null
  [[ -f "$pid_file" ]] || { echoRed "Not running"; return 3; }
  pid=$(cat "$pid_file")
  isRunning "$pid" || { echoRed "Not running (process ${pid} not found)"; return 1; }
  echoGreen "Running [$pid]"
  return 0
}

run() {
  pushd "$(dirname "$jarfile")" > /dev/null
  "$javaexe" "${arguments[@]}"
  result=$?
  popd > /dev/null
  return "$result"
}

# Call the appropriate action function
case "$action" in
start)
  start "$@"; exit $?;;
stop)
  stop "$@"; exit $?;;
force-stop)
  force_stop "$@"; exit $?;;
restart)
  restart "$@"; exit $?;;
force-reload)
  force_reload "$@"; exit $?;;
status)
  status "$@"; exit $?;;
run)
  run "$@"; exit $?;;
*)
  echo "Usage: $0 {start|stop|force-stop|restart|force-reload|status|run}"; exit 1;
esac

exit 0

5. Reference

Discussion

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