13 posts tagged with "Java"

Setup

November 2, 2022 · One min read

Mirrors

Add mirror in conf/setting.xml file in Maven root folder:

<mirrors>
    <mirror>
      <id>alimaven</id>
      <name>aliyun maven</name>
      <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
      <mirrorOf>central</mirrorOf>        
    </mirror>
</mirrors>

Spring Boot Logging

July 16, 2021 · One min read

Open in Notion

TRACE
DEBUG
INFO
WARN
ERROR
FATAL

Java Versions and JDK Versions

January 25, 2021 · One min read

Open in Notion

Versions and JDK

Java SE Version	JDK Version	Class Version	Released Date
Java SE 6 (Mustang)	1.6	50	December 2006
Java SE 7 (Dolphin)	1.7	51	July 2011
Java SE 8	1.8	52	March 2014
Java SE 9	9	53	September, 21st 2017
Java SE 10	10	54	March, 20th 2018
Java SE 11	11	55	September, 25th 2018

Install on CentOS

yum list *openjdk*
yum install java-<version here>-openjdk    # e.g java-11-openjdk
update-alternatives --config java    # choose the default java version
java -version

Install via sdkman

curl -s https://get.sdkman.io | bash

sdk list java
sdk install java <version>  // for example `sdk install java 11.0.12-open`

sdk current
sdk current java

Monitor File Changes

January 20, 2021 · One min read

Open in Notion

public static void main(String[] args) throws Exception {
 
   WatchService watchService = FileSystems.getDefault().newWatchService();

   Path path = Paths.get("G:\\");

   path.register(
       watchService,
       StandardWatchEventKinds.ENTRY_CREATE,
       StandardWatchEventKinds.ENTRY_DELETE,
       StandardWatchEventKinds.ENTRY_MODIFY);

   WatchKey key;
   while ((key = watchService.take()) != null) {
       for (WatchEvent<?> event : key.pollEvents()) {
          System.out.println("Event:" + event.kind() + ", File：" + event.context());
       }
       key.reset();
   }
}

WatchService added in Java7 for NIO solution.

Monitor Spring Boot Application

January 20, 2021 · One min read

Open in Notion

bookmark

Host Your Sentry

git clone https://github.com/getsentry/onpremise.git
cd onpremise
./install.sh

Once your Sentry is ready, you need to create your project with Spring Boot or Java platform in your Sentry.

Set up Spring Boot Application

Get Started

<dependency>
  <groupId>io.sentry</groupId>
  <artifactId>sentry-spring-boot-starter</artifactId>
  <version>3.1.1</version>
</dependency>

sentry.dsn=https://key@host/id

Who send the exception?

You can use SentryUserProvider to build a Java Bean:

@Bean
    public SentryUserProvider sentryUserProvider(){
        return () -> {
            // TODO: get your current user
            User user = new User();
            user.setId("userId");
            user.setUsername("Bendy");
            user.setEmail("zb@bndy.net");

            return user;
        };
    }

Custom Tags

@Bean
    public SentryOptions.BeforeSendCallback beforeSendCallback(){
        return (event, hint) -> {
            event.setTag("name","zhangsan");
            return event;
        };
    }

Integration with Logback

<dependency>
  <groupId>io.sentry</groupId>
  <artifactId>sentry-logback</artifactId>
  <version>3.1.1</version>
</dependency>

@RestController
public class HelloController {
    private static Logger logger = LoggerFactory.getLogger(HelloController.class);

    @RequestMapping("/")
    public void test(){
        logger.error("Logback error!");
    }
}

Spring Boot with Keycloak

January 20, 2021 · 4 min read

Open in Notion

bookmark

The Keycloak Spring Boot adapter capitalizes on Spring Boot’s auto-configuration, so all we need to do is add the Keycloak Spring Boot starter to our project.

Within the dependencies XML element, we need the following to run Keycloak with Spring Boot:

<dependency>
    <groupId>org.keycloak</groupId>
    <artifactId>keycloak-spring-boot-starter</artifactId>
</dependency>

After the dependencies XML element, we need to specify dependencyManagement for Keycloak:

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.keycloak.bom</groupId>
            <artifactId>keycloak-adapter-bom</artifactId>
            <version>11.0.2</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

The following embedded containers are supported now and don't require any extra dependencies if using Spring Boot Keycloak Starter:

Tomcat
Undertow
Jetty

Keycloak Configuration

Here's the basic, mandatory configuration:

keycloak.realm = <REALM_NAME>
keycloak.auth-server-url = http://127.0.0.1:8080/auth
keycloak.ssl-required = external
keycloak.resource = <CLIENT_ID>
keycloak.credentials.secret = <CLIENT_SECRET>
keycloak.use-resource-role-mappings = true
keycloak.bearer-only = true

You can disable the Keycloak Spring Boot Adapter (for example in tests) by setting keycloak.enabled = false.

To configure a Policy Enforcer, unlike keycloak.json, policy-enforcer-config must be used instead of just policy-enforcer.

You also need to specify the Java EE security config that would normally go in the web.xml. The Spring Boot Adapter will set the login-method to KEYCLOAK and configure the security-constraints at startup time. Here’s an example configuration:

keycloak.securityConstraints[0].authRoles[0] = admin
keycloak.securityConstraints[0].authRoles[1] = user
keycloak.securityConstraints[0].securityCollections[0].name = insecure stuff
keycloak.securityConstraints[0].securityCollections[0].patterns[0] = /insecure

keycloak.securityConstraints[1].authRoles[0] = admin
keycloak.securityConstraints[1].securityCollections[0].name = admin stuff
keycloak.securityConstraints[1].securityCollections[0].patterns[0] = /admin

If you plan to deploy your Spring Application as a WAR then you should not use the Spring Boot Adapter and use the dedicated adapter for the application server or servlet container you are using. Your Spring Boot should also contain a web.xml file.

KeycloakSecurityConfig.java

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(jsr250Enabled = true)
public class KeycloakSecurityConfig extends KeycloakWebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        super.configure(http);
        http.authorizeRequests()
            .anyRequest()
            .permitAll();
        http.csrf().disable();
    }

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        KeycloakAuthenticationProvider keycloakAuthenticationProvider = keycloakAuthenticationProvider();
        keycloakAuthenticationProvider.setGrantedAuthoritiesMapper(new SimpleAuthorityMapper());
        auth.authenticationProvider(keycloakAuthenticationProvider);
    }

    @Bean
    @Override
    protected SessionAuthenticationStrategy sessionAuthenticationStrategy() {
        return new RegisterSessionAuthenticationStrategy(new SessionRegistryImpl());
    }

    @Bean
    public KeycloakConfigResolver KeycloakConfigResolver() {
        return new KeycloakSpringBootConfigResolver();
    }
}

configureGlobal: Registers the KeycloakAuthenticationProvider with the authentication manager.

sessionAuthenticationStrategy: Defines the session authentication strategy.

KeycloakConfigResolver : By Default, the Spring Security Adapter looks for a keycloak.json configuration file. You can make sure it looks at the configuration provided by the Spring Boot Adapter by adding this bean

@EnableGlobalMethodSecurity: The jsr250Enabled property allows us to use the @RoleAllowed annotation. We’ll explore more about this annotation in the next section.

TestController.java

@RestController
@RequestMapping("/test")
public class TestController {

    @RequestMapping(value = "/anonymous", method = RequestMethod.GET)
    public ResponseEntity<String> getAnonymous() {
        return ResponseEntity.ok("Hello Anonymous");
    }

    @RequestMapping(value = "/user", method = RequestMethod.GET)
    public ResponseEntity<String> getUser() {
        return ResponseEntity.ok("Hello User");
    }

    @RequestMapping(value = "/admin", method = RequestMethod.GET)
    public ResponseEntity<String> getAdmin() {
        return ResponseEntity.ok("Hello Admin");
    }

    @RequestMapping(value = "/all-user", method = RequestMethod.GET)
    public ResponseEntity<String> getAllUser() {
        return ResponseEntity.ok("Hello All User");
    }
}

Run the Spring Boot Application. Make sure Maven is installed and configured.

mvn spring-boot:run

As defined in the TestController, let’s invoke the REST APIs with CURL one by one.

curl -X GET 'http://localhost:8000/test/anonymous'
curl -X GET 'http://localhost:8000/test/user'
curl -X GET 'http://localhost:8000/test/admin'
curl -X GET 'http://localhost:8000/test/all-user'

As you see all APIs don’t require any authentication or authorization. Now let’s try to secure these API endpoints.

Define Role-Based Access with @RolesAllowed Annotation

@RolesAllowed("user")
@RequestMapping(value = "/user", method = RequestMethod.GET)
public ResponseEntity<String> getUser(@RequestHeader String Authorization) {
    return ResponseEntity.ok("Hello User");
}

@RolesAllowed("admin")
@RequestMapping(value = "/admin", method = RequestMethod.GET)
public ResponseEntity<String> getAdmin(@RequestHeader String Authorization) {
    return ResponseEntity.ok("Hello Admin");
}

@RolesAllowed({ "admin", "user" })
@RequestMapping(value = "/all-user", method = RequestMethod.GET)
public ResponseEntity<String> getAllUser(@RequestHeader String Authorization) {
    return ResponseEntity.ok("Hello All User");
}

Define Role-Based Access with Security Configuration

Rather than using @RolesAllowed annotation, the same configuration can be made in KeycloakSecurityConfig class as below.

@Override
protected void configure(HttpSecurity http) throws Exception {
    super.configure(http);
    http.authorizeRequests()
        .antMatchers("/test/anonymous").permitAll()
        .antMatchers("/test/user").hasAnyRole("user")
        .antMatchers("/test/admin").hasAnyRole("admin")
        .antMatchers("/test/all-user").hasAnyRole("user","admin")
        .anyRequest()
        .permitAll();
    http.csrf().disable();
}

Java 8 Stream Tutorial

January 18, 2021 · 2 min read

Open in Notion

List<String> myList =
    Arrays.asList("a1", "a2", "b1", "c2", "c1");

myList
    .stream()
    .filter(s -> s.startsWith("c"))
    .map(String::toUpperCase)
    .sorted()
    .forEach(System.out::println);

// C1
// C2

Arrays.asList("a1", "a2", "a3")
    .stream()
    .findFirst()
    .ifPresent(System.out::println);  // a1

Stream.of("a1", "a2", "a3")
    .findFirst()
    .ifPresent(System.out::println);  // a1

IntStream, LongStream, DoubleStream

IntStream.range(1, 4)
    .forEach(System.out::println);
// 1
// 2
// 3

IntStream.range(1, 4)
    .mapToObj(i -> "a" + i)
    .forEach(System.out::println);
// a1
// a2
// a3

Processing Order

Stream.of("d2", "a2", "b1", "b3", "c")
    .filter(s -> {
        System.out.println("filter: " + s);
        return true;
    })
    .forEach(s -> System.out.println("forEach: " + s));

filter:  d2
forEach: d2
filter:  a2
forEach: a2
filter:  b1
forEach: b1
filter:  b3
forEach: b3
filter:  c
forEach: c

Stream.of("d2", "a2", "b1", "b3", "c")
    .map(s -> {
        System.out.println("map: " + s);
        return s.toUpperCase();
    })
    .anyMatch(s -> {
        System.out.println("anyMatch: " + s);
        return s.startsWith("A");
    });

// map:      d2
// anyMatch: D2
// map:      a2
// anyMatch: A2

Stream.of("d2", "a2", "b1", "b3", "c")
    .sorted((s1, s2) -> {
        System.out.printf("sort: %s; %s\n", s1, s2);
        return s1.compareTo(s2);
    })
    .filter(s -> {
        System.out.println("filter: " + s);
        return s.startsWith("a");
    })
    .map(s -> {
        System.out.println("map: " + s);
        return s.toUpperCase();
    })
    .forEach(s -> System.out.println("forEach: " + s));

parallelStream()

List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
long count = strings.parallelStream().filter(string -> string.isEmpty()).count();

summaryStatistics()

List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
 
IntSummaryStatistics stats = numbers.stream().mapToInt((x) -> x).summaryStatistics();
 
System.out.println("Max: " + stats.getMax());
System.out.println("Min: " + stats.getMin());
System.out.println("Sum: " + stats.getSum());
System.out.println("Avg: " + stats.getAverage());

AOP – Aspect-oriented programming

May 29, 2020 · 4 min read

Open in Notion

It does so by adding additional behavior to existing code (an advice) without modifying the code itself, instead separately specifying which code is modified via a “pointcut” specification, such as “log all function calls when the function’s name begins with ‘set’”. This allows behaviors that are not central to the business logic (such as logging) to be added to a program without cluttering the code, core to the functionality. AOP forms a basis for aspect-oriented software development.

Define an Aspect by using @Aspect annotations – which is natively understood by Spring:

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@Aspect
public class AuditAspect {

    private static Logger logger = LoggerFactory.getLogger(AuditAspect.class);

    @Pointcut("execution(* net.bndy.service.*.*(..))")
    public void serviceMethods(JoinPoint jp){ }

    // Intercept all calls to methods annotated with @PerLog
    // @Pointcut("execution(@net.bndy.annotations.PerfLog * *.*(..))")
    public void performanceTargets(JoinPoint jp, PerLog perLog){ }
    // Pass annotation to AOP advices
    @Pointcut(value = "@annotation(perLog)", argNames = "perfLog")
    public void performanceTargets(JoinPoint jp, PerLog perLog){ }

    // Using annotations and parameters in AOP advices
    @Before(value = "com.byteslounge.spring.aop.PointcutDefinition.serviceLayer() && args(account,..) && @annotation(auditable)")
    public void audit(Account account, Auditable auditable) {
        System.out.println("Audit account access: "
            + account.getAccountNumber() + ". Audit destination: "
            + auditable.value());
    }

    // If the first parameter is of the JoinPoint, ProceedingJoinPoint, or JoinPoint.StaticPart type, you may leave out the name of the parameter from the value of the "argNames" attribute. For example, if you modify the preceding advice to receive the join point object, the "argNames" attribute need not include it:
    @Before(value="com.xyz.lib.Pointcuts.anyPublicMethod() && target(bean) && @annotation(auditable)", argNames="bean,auditable")
    public void audit(JoinPoint jp, Object bean, Auditable auditable) {
        AuditCode code = auditable.value();
        // ... use code, bean, and jp
    }

    @Before("serviceMethods()")
    public void beforeMethod(JoinPoint jp) {
        String methodName = jp.getSignature().getName();
        logger.info("before method:" + methodName);
    }

    @Around("serviceMethods()")
    public Object aroundMethod(ProceedingJoinPoint jp) {
        try {
            long start = System.nanoTime();
            // execute target method
            Object result = jp.proceed();
            long end = System.nanoTime();
            logger.info(String.format("%s took %d ns", jp.getSignature(), (end - start)));
            return result;
        } catch (Throwable e) {
            throw new RuntimeException(e);
        }
    }

    // Always run if method completed
    @After("serviceMethods()")
    public void afterMethod(JoinPoint jp) {
        logger.info("after method");
    }

    // Run when the method returns normally.
    @AfterReturning(value="execution(* net.bndy.service.*.*(..))",returning="result")
    public void afterReturningMethod(JoinPoint jp, Object result){ }

    // Run if an exception has benn thrown in method
    @AfterThrowing(value="execution(* net.bndy.service.*.*(..))",throwing="e")
    public void afterThorwingMethod(JoinPoint jp, NullPointerException e){ }
}

@Pointcut

//                   Any return type | package          | class | method | any type and number of arguments
@Pointcut("execution(*                 net.bndy.service . *.      *(       ..                                  ))")
@Pointcut("execution(* net.bndy.service.*.*(.. ))")

// examples
@Pointcut("within(*..*Test)")                   // support for sub packages is provided with ".."
@Pointcut("within(net.bndy.service..*Test)")    // ends with Test inside the "net.bndy.service" package
@Pointcut("!within(net.bndy.service..*Test)"    // expects that ends with Test inside the "net.bndy.service" package
@Pointcut("execution(void *..service.Service+.*(..))")  // all methods in the Service class or a subtype of it

@Pointcut("!withincode(@org.junit.Test * *(..))")    //Finds all statements that’s not inside a method marked with @Test

// other Pointcuts
//execution(void Point.setX(int))
//call(void Point.setX(int))
//handler(ArrayOutOfBoundsException)
//this(SomeType)
//target(SomeType)
//within(MyClass)
//cflow(call(void Test.main()))
//call(* *(..)) &amp;&amp; (within(Line) || within(Point))
//execution(!static * *(..))
//execution(public !static * *(..))

Why to use argNames

public class HelloApi {

    public void aspectTest(String a,String b){
        System.out.println("in aspectTest:" + "a:" + a + ",b:" + b);
    }
}

@Pointcut(value="execution(* bean.HelloApi.aspectTest(..)) && args(a1,b2)",argNames="a1,b2")
public void pointcut1(String a1,String b2){}

@Before(value="pointcut1(a,b)",argNames="a,b")
public void beforecase1(String a,String b){
    System.out.println("1 a:" + a +" b:" + b);
}

// NOTE: a and p locations
@Before(value="pointcut1(a,b)",argNames="b,a")
public void beforecase2(String a,String b){
    System.out.println("2 a:" + a +" b:" + b);
}

HelloApi helloapi1 = beanFactory.getBean("helloapi1",HelloApi.class);
helloapi1.aspectTest("a", "b");

Output

1 a:a b:b
2 a:b b:a
in aspectTest:a:a,b:b

Build Spring Boot Starter Project

May 29, 2020 · One min read

Open in Notion

Two Java Files

@ConfigurationProperties(prefix = "spring.ftsi")
public class IndexServiceAutoConfigurationProperties {

}

@Configuration
@EnableConfigurationProperties(IndexServiceAutoConfigurationProperties.class)
@ConditionalOnClass(IndexService.class)
@ConditionalOnProperty(prefix = "spring.ftsi", name = "enabled", matchIfMissing = true)
public class IndexServiceAutoConfiguration {

    @Autowired
    private IndexServiceAutoConfigurationProperties properties;

    @Bean
    @ConditionalOnMissingBean(IndexService.class)
    public IndexService indexService() throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        IndexService service = new IndexService();
        return service;
    }
}

File: /src/main/resources/META-INF/spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
net.bndy.ftsi.starter.IndexServiceAutoConfiguration

Usage

application.yml

spring:
  ftsi:
    property1: ...
    property2: ...

java

@SpringBootApplication
public class Application {

    @Autowried
    IndexService indexService;

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Enable https in Spring Boot

May 29, 2020 · One min read

Open in Notion

Create Self Signed SSL Certificate

keytool -genkeypair -alias filenameAlias -keyalg RSA -keysize 2048 -storetype PKCS12 -keystore filename.p12 -validity 3650

And use below code to view certificate details.

keytool -list -keystore  filename.p12

Enabling HTTPS in Spring Boot application.propreties

# The format used for the keystore. for JKS, set it as JKS
  server.ssl.key-store-type=PKCS12
# The path to the keystore containing the certificate
  server.ssl.key-store=classpath:keystore/javadevjournal.p12
# The password used to generate the certificate
server.ssl.key-store-password=use the same password which we added during certificate creation
# The alias mapped to the certificate
  server.ssl.key-alias=javadevjournal
# Run Spring Boot on HTTPS only, default 443 like no https 80 port
server.port=8443

Note that you need copy filename.p12 to src/main/resources/keystore folder

Mirrors​

Versions and JDK​

Install on CentOS​

Install via sdkman​

Host Your Sentry​

Set up Spring Boot Application​

Get Started​

Who send the exception?​

Custom Tags​

Integration with Logback​

Keycloak Configuration

KeycloakSecurityConfig.java

TestController.java

Define Role-Based Access with @RolesAllowed Annotation​

Define Role-Based Access with Security Configuration​

IntStream, LongStream, DoubleStream​

Processing Order​

parallelStream()​

summaryStatistics()​

Define an Aspect by using @Aspect annotations – which is natively understood by Spring:​

@Pointcut​

Why to use argNames​

Two Java Files​

File: /src/main/resources/META-INF/spring.factories​

Usage​

Mirrors

Versions and JDK

Install on CentOS

Install via sdkman

Host Your Sentry

Set up Spring Boot Application

Get Started

Who send the exception?

Custom Tags

Integration with Logback

Define Role-Based Access with @RolesAllowed Annotation

Define Role-Based Access with Security Configuration

IntStream, LongStream, DoubleStream

Processing Order

parallelStream()

summaryStatistics()

Define an Aspect by using @Aspect annotations – which is natively understood by Spring:

@Pointcut

Why to use argNames

Two Java Files

File: /src/main/resources/META-INF/spring.factories

Usage