Validate JAVA Http Client Codegen and add relevant testcases

[apoorvdwi]

PR Description

This PR fixes the Java http client codegen and adds the relevant tests.

Related Issues

• Related Issue #137
• Closes #137

Checklist

• [x] I have gone through the contributing guide
• [x] I have updated my branch and synced it with project main branch before making this PR
• [x] I have run the tests (flutter test) and all tests are passing

Added/updated tests?

We encourage you to add relevant test cases.

• [x] Yes

Steps to run

Java code is relatively hard to run on local machine due to install overheads which is why I prepared a simple dockerfile given below

# Use the official OpenJDK image for a base image
FROM openjdk:23

# Set the working directory inside the container
WORKDIR /usr/src/myapp

# Copy the Main.java file from the local directory to the container's working directory
COPY Main.java /usr/src/myapp/
COPY 1.png /usr/src/myapp/

# Include Gson JAR file (assuming it is available locally)
COPY gson-2.8.9.jar /usr/src/myapp/

# Add Gson JAR file to the classpath
ENV CLASSPATH=.:/usr/src/myapp/gson-2.8.9.jar

# Compile the Java program
RUN javac Main.java

# Run the Java program when the container launches
CMD ["java", "Main"]

• Put this in a folder with a file called Main.java and paste the code you want to run in the file
• Download the gson jar file from here and put it in the same folder
• Put any image in the same folder as well and either rename it to 1.png or change in the dockerfile and image can be used in formdata with path /usr/src/myapp/<filename>
• execute the below command

  docker build -t java-app . && docker run --rm java-app

[apoorvdwi]

@ashitaprasad @animator please review this PR Let me know if you face any difficulties in running the code

I'm pasting a few screenshots of code runs just in case

[animator]

POST 2 & POST 3 generated code is giving incorrect output.

Response body: {"detail":[{"type":"model_attributes_type","loc":["body"],"msg":"Input should be a valid dictionary or object to extract fields from","input":"{\n\"text\": \"I LOVE Flutter\"\n}","url":"https://errors.pydantic.dev/2.6/v/model_attributes_type"}]}
Response code: 422

Expected Output:

Response body: {"data":"i love flutter"}
Response code: 200

[animator]

Also HEAD2 is

codeGen.getCode(
              CodegenLanguage.javaHttpClient, requestModelHead2, "http"),
          expectedCode);

instead of

codeGen.getCode(
              CodegenLanguage.javaHttpClient, requestModelHead2, "https"),
          expectedCode);

[apoorvdwi]

@ashitaprasad @animator fixed the head2 testcase and json body type parsing

[animator]

Thanks for the PR. LGTM 🚀