Blogger API fetch drafts

Google provides APIs to integrate your system with existing Google services for various purpose. I started exploring APIs related to Blogger for this Blog to automate things and building a convinient system of writing and publishing blog. I came across with one scenario which I would like to share.

While fetching the drafts with the help of Blogger API v3, I realized the API was not returning the drafts. Even after supplying the post id or the status it was returning 404 Not Found.

draft_post = service.posts().get(blogId=blog_id, postId=post_id).execute()

This is an intended behavior from the API, for some reason the GET API is not returning the draft post. Following was a loose attempt to make it work, but failed. However, every other source was claiming this to be working, but wasn’t.

draft_post = service.posts().get(blogId=blog_id, postId=post_id, status='DRAFT').execute()

While looking for the solution in different sources, I found this 4 year old thread,

Unable to retrieve “scheduled” and “draft” posts while using the blooger v3 api

So, I had no option but to switch to this method of fetching the draft post, it’s not a cleaner way but still, nothing else I can do about it. The solution looks like this,

draft_posts = service.posts().list(blogId=blog_id, status='DRAFT').execute()

if 'items' in draft_posts:
    for post in draft_posts['items']:
        if post['id'] == post_id:
            print("Draft post found.")
else:
    print("No draft posts found")

Same thing applies to scheduled post as well, we have to fetch all the posts and filter respectively. It’s not something related to the python library, with other languages as well the same result is being returned.

I spend some time to identify why the API is not returning unpublished post with the help of GET API but couldn’t find any official clarification for the same. I feel, it’s by design not returning the unpublished ones to avoid any repercussions while doing some operations on the returned post considering them as published.

Java 9 to 19

Java 8 is still extensively used in the industry and many applications will gradually shift to newer Java version, especially the LTS versions.

In this post we will take a look at the evolution happened in Java language from Java 9 to Java 19. Note that each version comes with many improvements, bug fixes and variety of features, we will cover the ones which are majorly used and can impact our day to day developement.

Java 9

Factory methods for collection

    List immutableL = List.of(1, 2, 3);
    Map immutableM = Map.of(1, "ONE", 2, "TWO", 3, "THREE")

JShell: Java Shell, or REPL (Read Evaluate Print Loop) to execute java constructs directly in command line.

Private methods in interface.

This will avoid code duplication and better separation of concern when it comes to implementing default and static methods in interface.

interface Student {
    private String joinNames(String firstName, String lastName) {
        return String.join(firstName, " ",lastName);
    }
    private static String schoolName() {
        return "Some School";
    }

    default String id(String firstName, String lastName) {
        String fullName = joinNames(firstName, lastName);
        return schoolName() + "\n" + fullName;
    }
}

Step in direction to optimize String concatenation.

For the given class,

public class Test {
    public static void main(String[] args) {
        String str = args[0] + " and " + args[1];
    }
}

If we compile and check the bytecode, we can notice significant different in the way concatenation is handled.

In Java 8,

➜  java git:(main) ✗ java -version 
openjdk version "1.8.0_362"
OpenJDK Runtime Environment (build 1.8.0_362-bre_2023_01_22_03_30-b00)
OpenJDK 64-Bit Server VM (build 25.362-b00, mixed mode)
➜  java git:(main) ✗ clear           
➜  java git:(main) ✗ java -version
openjdk version "1.8.0_362"
OpenJDK Runtime Environment (build 1.8.0_362-bre_2023_01_22_03_30-b00)
OpenJDK 64-Bit Server VM (build 25.362-b00, mixed mode)
➜  java git:(main) ✗ javac Test.java
➜  java git:(main) ✗ javap -c  Test 
Compiled from "Test.java"
public class Test {
  public Test();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class java/lang/StringBuilder
       3: dup
       4: invokespecial #3                  // Method java/lang/StringBuilder."<init>":()V
       7: aload_0
       8: iconst_0
       9: aaload
      10: invokevirtual #4                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      13: ldc           #5                  // String  and
      15: invokevirtual #4                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      18: aload_0
      19: iconst_1
      20: aaload
      21: invokevirtual #4                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      24: invokevirtual #6                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      27: astore_1
      28: return
}

In Java 9,

➜  java git:(main) ✗ java -version 
openjdk version "9"
OpenJDK Runtime Environment (build 9+181)
OpenJDK 64-Bit Server VM (build 9+181, mixed mode)
➜  java git:(main) ✗ javac Test.java
➜  java git:(main) ✗ javap -c  Test 
Compiled from "Test.java"
public class Test {
  public Test();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: aload_0
       1: iconst_0
       2: aaload
       3: aload_0
       4: iconst_1
       5: aaload
       6: invokedynamic #2,  0              // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
      11: astore_1
      12: return
}

Notice the multiple StringBuilder invocations in case of Java 8, which is replaced with makeConcatWithConstants in Java 9.

Java 10

Local variable type interface, use var to declare.

    var i = 1;
    var str = "Hello";
    var student = getStudent();

Static factory methods to create immutable copy of Collection,

    List<String> immutable = List.copyOf(otherList);

orElseThrow() in Optional

    Optional<Object> optional = Optional.ofNullable(null);
    optional.orElseThrow(() -> new RuntimeException("Something went wrong!"));

Java 11 (LTS)

Execute Java file directly without compiling with javac.

java command internally takes care of the compilation.

Some helper methods for String

String str = "Hello";
boolean isBlank = str.isBlank();
str.lines().forEach(System.out::println);
str = str.strip();
// str.stripLeading();
//  str.stripTrailing();

Removed deprecated packages,

java.xml.ws
java.xml.bind
java.activation
java.xml.ws.annotation
java.corba
java.transaction
java.se.ee
jdk.xml.ws
jdk.xml.bind

Make file read and write convenient,

Path path = Files.writeString(Files.createTempFile("temporary", ".txt"), "Something to write!");

String fileContent = Files.readString(path);
System.out.println(fileContent);

Java 12

Switch can be an expression, changes are in preview.

Before Java 12

Animals animal = Animals.COW;

switch (animal) {
    case COW:
    case GOAT:
        System.out.println("Herbivore");
        break;
    case TIGER:
    case LION:
        System.out.println("Carnivore");
        break;
}

Can now be reduced to,

String animalType = switch (animal) {
    case COW, GOAT -> "Herbivore";
    case TIGER,  LION -> "Carnivore";
};

No need to typecast for instanceof,

if(object instanceof String) {
    System.out.println(((String)object).toUpperCase());
}

but now you can do,

if(object instanceof String str) {
    System.out.println(str.toUpperCase());
}

Compare files,

try {
    Path filePath1 = Files.createTempFile("abc1", ".txt");
    Path filePath2 = Files.createTempFile("abc2", ".txt");

    Files.writeString(filePath1, "Hello!");
    Files.writeString(filePath2, "Hello! (Diff)");

    long mismatchIndex = Files.mismatch(filePath1, filePath2);
    if(mismatchIndex == -1) {
        System.out.println("Both files are same!");
    } else {
        System.out.println("Mismatch found at " + mismatchIndex);
    }
} catch (IOException e) {
    throw new RuntimeException(e);
}

Output

Mismatch found at 6

String Identation,

String str = "Hello";
for(int i = 0 ; i < 5; i++) {
    System.out.print(str.indent(i));
}

Output

Hello
 Hello
  Hello
   Hello
    Hello

Convenient method to transform String,

String numbers = "1:ONE,2:TWO,3:THREE";
Map<Integer, String> map = numbers.transform(input -> {
    Map<Integer, String> output =
        Arrays.stream(input.split(","))
            .collect(Collectors.toMap(i -> Integer.parseInt(i.split(":")[0]),
                i -> i.split(":")[1]));
    return output;
});
System.out.println(map);

Java 13

Text block support in String,

String textBlock = """
    I can write anything,
    without adding \\n in the String.
    """;
System.out.println(textBlock);

New Methods in String for format,

String anything = "Hello %d and %s".formatted(1, "ONE");

Intoduced yield in switch case, this will replace the break for cases where we want to return the number. Difference between yeild and return is that yeild will return the value to switch invocation while return will return the value to the caller of the method.

int answer = switch (number) {
    case 1:
    case 3:
    case 5:
    case 7:
        yield number;
    default:
        yield -1;
};

Java 14

Preview of records, a data class.

record Person(String name, int age){}

Can be used,

Person person = new Person("Human", 999);
System.out.printf("Person %s, age %d\n", person.name(), person.age());

Things to note about record

  • Can not extend, can not be extended by class
  • Can not be abstract
  • Allows static fields and methods
  • Instance fields can be declared during initialization.
  • Declared fields are private and final
record Person(String name, int age){
    // int anything = 0; // Not allowed
    static int anything = 0;

    public String personDetails() {
        return String.format("Person %s, age %d\n", name(), age());
    }
    Person {
        if(name == "Human") {
            throw new RuntimeException("Invalid name");
        }
    }
}

Records can implement interfaces,

interface Human {
    public String personDetails();
}

record Person(String name, int age) implements Human{
    public String personDetails() {
        return String.format("Person %s, age %d\n", name(), age());
    }
}

It can support multiple constructors as well,

record Person(String name, int age){
    public Person() {
        this("Human", 9999);
    }
    public Person (int age) {
        this("Human", age);
    }
}

Allow trailing space in text block,

String textBlock = """
    I can write anything,
    without adding \\n in the String.\s\s\s
    """;
System.out.println(textBlock);

Java 15

Preview of sealed classes or interfacse,

to allow only specific types which can extend or implement respectively.

public abstract sealed class Animal permits Herbivore, Carnivore {
}

final class Herbivore extends Animal{}
sealed class Carnivore extends Animal{}

//class Unknown extends Animal{} // Not allowed to extend

Subclass of a sealed class must have either of the following modifiers,

  • sealed : Will allow to be extended further by permitted classes.
  • non-sealed : Will allow to be extended further by any classes.
  • final : Will not allow to be extended further.
public abstract sealed class Animal permits Herbivore, Carnivore, Omnivore {
}

final class Herbivore extends Animal {}
sealed class Carnivore extends Animal permits  Tiger{}
non-sealed class Omnivore extends Animal {}

final class Tiger extends Carnivore{}

Records can implement the sealed interfaces,

sealed interface Food permits Creature {
    void doSomething();
} 
record Creature(String name) implements Food {
    @Override
    public void doSomething() {
        System.out.println("Anything");
    }
}

Java 16

Pattern matching in instanceof no longer makes variable implicitly final

if(object instanceof String) {
    object = String.format("Result %s", object); // Would give compile time error prior to Java 16.
    System.out.println(object.toUpperCase());
}

New Vector API, incubator.

int[] odd = {1, 3, 5, 7};
int[] even = {2, 4, 6, 8};
var vector1 = IntVector.fromArray(IntVector.SPECIES_128, odd, 0);
var vector2 = IntVector.fromArray(IntVector.SPECIES_128, even, 0);
var vector3 = vector1.add(vector2);
System.out.println(vector3);

Output

[3, 7, 11, 15]

Note that, to run the program you will need to add the module otherwise it won’t be visible.

 java --add-modules jdk.incubator.vector JavaMainClass

Java 17 (LTS)

null in switch,

switch (number) {
    case 1, 2, 3 -> System.out.println("Valid");
    case null -> System.out.println("Not available");
    default -> System.out.println("Invalid");
}

Pattern matching in switch,

String value = switch (obj) {
    case Integer i -> "Integer";
    case Long l    -> "Long";
    case Double d  -> "Double";
    case String s  -> "String";
    case null -> "NULL";
    default -> obj.toString();
};

Java 18

Introduce @snippet in JavaDoc to write code in comments,

/**
* {@snippet:
*  int a = 10;
* }
*/
public void testMethod() {

}

Finalization is deprecated.

The use of finalize() method is discouraged and the support will be removed in future.

Java 19

Preview Virtual Threads

lightweight threads which effectively shares the platform thread for optimal hardware utilisation.

ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor();

Structured Concurrency (Incubator)

Sounds interesting, it enables to consider multiple threads as a unit. This will going to give better control over multithreaded programs.

Basics of Spring Transactional

Why Spring Transaction?

  • Provides consistent model across JTA (Java Transaction API), JPA (Java Persistence API), JDBC (Java Database Connectivity) and JDO (Java Data Objects)
  • Declarative Transaction Management
  • Simple API for programmatic transaction management - overcomes complexity of JTA.
  • Makes the implementation easy to stub and test.

Transaction with JDBC

import java.sql.Connection;

//...
public void deleteSomething() {
    Connection connection = DriverManager.getConnection(host, user, password); 

    try (connection) {
        connection.setAutoCommit(false);
        Statement deleteStatement = connection.createStatement(); 
        String deleteQuery = "DELETE FROM SOMETHING WHERE SOMETHING_ID = 1";
        deleteStatement.executeQuery(deleteQuery); 
        connection.commit();
    } catch (SQLException e) {
        connection.rollback();
    }
}

//...
With raw JDBC we need to handle commit, rollback, savepoint all on our own. Spring takes away majority of boilerplate code so that we can focus on core business functionalities. 

Transaction with Spring

Above function can be implemented in following way with Spring (assuming the transaction management configuration is in place),

@Transactional
public void deleteSomething() {
    somethingRepository.deleteBySomethingId(1);
}

Spring Transaction Manager




Spring transaction manager mainly rely on definition and status. In definition the nature and behaviour of transaction is defined while the status helps to keep track of transaction journey statuses.

Different Supported transaction managers includes,
  •  DataSourceTransactionManager
  •  JtaTransactionManager
  •  HibernateTransactionManager
  •  JdbcTransactionManager
  •  etc.
This Transactional annotation handles everything behind the scene for use. This annotation has two important configurations - Isolation and Propagation, which we will understand in detail.

Propagation

Transcation propagation defines the nature of transaction handling when there are multiple transactional annottated methods are invoked within the same spring transcation context. 

You can suppy the propagation in Transactional annotation,

@Transactional(propagation = Propagation.REQUIRES_NEW)

Following are supported propagation ways,

  • REQUIRED  → Create new transcation or use existing.
  • SUPPORTS  → Work with or without transaction.
  • MANDATORY  → Do not create transaction but fail if transaction do not exist.
  • REQUIRES_NEW  → Create a new transaction.
  • NOT_SUPPORTED  → Execute without transaction, suspend if transaction exists.
  • NEVER  → Execute without transaction, fail if transaction exists.
  • NESTED  → One physical transaction with multiple savepoints to manage subtransactions.
















Isolation

Isolation level configuration determines the visibility of data between transactions in case of concurrent operations on same database resource. It helps to ensure consistency and integrity of the data. Transaction isolation level is subject to underlying database you are using. We will refer to them in generic sense to get glimps of it.

You can suppy the isolation in Transactional annotation,

@Transactional(isolation = Isolation.DEFAULT)

The isolation levels tackles different concurrent transcation phenomena listed below,
  • Dirty Read : Transaction read uncommitted data of other transaction.
  • Non-repeatable read : Re-read the same data which is now modified by other transaction.
  • Phantom Read : Re-execute the query which returns result set which changed by other transcation.
  • Serialization Anomaly : Inconsistent state of data - group of transactions are committed sequentially with all possible ordering.

Following are supported isolations levels in Spring,
  • DEFAULT → User default isolation level of underlying database.
  • READ_UNCOMMITTED → Allows to read uncommitted data of other transaction. It can not prevent problems may arrise due to concurrency.
  • READ_COMMITTED →  Allows to read committed data of other transaction. Prevents dirty read.
  • REPEATABLE_READ → Prevents dirty read and non-repeatable read (and even phantom read) by returning unchanged data in repeatable reads within same transaction.
  • SERIALIZABLE → Executes transactions sequentially. Solves all consurrency problems but performance suffers.

This can be a starting point for spring transaction learnings, if you have understood the propagation and isolation level well, it becomes easier to configure and debug accordingly.