Showing posts with label java. Show all posts
Showing posts with label java. Show all posts

Java HttpClient tutorial with File Upload example

Java 11 comes with a nice HttpClient API/Implementation so that we no longer need to rely on external libraries like Apache HttpClient execute http requests.

It has the following simple classes(namely HttpClient, HttpRequest, HttpResponse, BodyPublisher, BodyHandler) and they all follow builder pattern to create objects.

Creating HttpClient:

HttpClient client = HttpClient.newBuilder().build();

Creating request:

HttpRequest request = HttpRequest.newBuilder()
.header("key1", "value1")
.header("key2", "value2")
.POST(HttpRequest.BodyPublishers.ofString("Request Body"))

Sending request:

client.send(request, HttpResponse.BodyHandlers.APPROPRIATE_HANDLER);

Here, BodyPublisher and BodyHandler can be used to create request body and process returned response respectively. They both support string, byte, file, input stream etc

Upload file using BodyPublishers.ofFile

Normally file upload using a web page are implemented using multi-part(file data with additional properties). But in this example we are going to upload file's byte array in request body and file name in request param.

import java.nio.file.Path;

public class HttpTest {
public static void main(String[] args) throws Exception {

public static void uploadFile(Path file) throws IOException, InterruptedException {
HttpClient client = HttpClient.newBuilder().build();

HttpRequest request = HttpRequest.newBuilder()
+ file.getFileName()))

client.send(request, HttpResponse.BodyHandlers.ofString());

To make the example complete, let's assume we have a following simple Spring Boot app that receives the file byte array as request body:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;


public class FileUploadApp {
public static void main(String[] args) {, args);

class FileUplCtrl {

@PostMapping(path = "/uploadFile")
public void addPhoto(@RequestBody byte[] barr,
@RequestParam(name = "uploader") String uploader,
@RequestParam(name = "fileName") String fileName) throws Exception {

System.out.println("Received file " + fileName + " , uploaded by " + uploader + " Size: " + barr.length);

//write to disk
try (OutputStream os = new FileOutputStream(new File("UPL" + fileName))) {


Required Dependency on Spring Boot app:


Enjoy coding!

Thymeleaf pass parameter to fragment

Making reusable fragment/UI Components in Thymeleaf

Thymeleaf supports creation of 'function like' mechanism and pass parameters to make the UI components reusable.

In this example we are going to create a reusable alert component using thymeleaf:

The fragment definition is similar to how a function/method is defined:

File: _fragments/_utils.html

<div th:fragment="alertBox(message,type)">
//do stuff with message and type

Let's call with some parameters in another file:

<div th:replace="_fragments/_utils::alertBox ('A message','success')">

The parameter order is not important if you do like this:

<div th:replace="_fragments/_utils::alertBox (type = 'success', message='A message' )">

A complete example:

<div th:fragment="alertBox (message,type)">
${type == 'success' ? 'alert-success': ''}
${type == 'info' ? 'alert-info': ''}
${type == 'danger' ? 'alert-danger': ''} |"
class="alert alert-dismissible">
<a href="#" class="close" data-dismiss="alert" aria-label="close">&times;</a>
<span th:text="${message}"></span>

Calling it:

<div th:replace="_fragments/_utils :: alertBox ('Hello this is a success!','success')">

<div th:replace="_fragments/_utils :: alertBox ('Danger! danger! .......','danger')">

<div th:replace="_fragments/_utils :: alertBox ( type = 'success', message='Success message' )">


Spring data Pagination - set max page size and other customizations


HandlerMethodArgumentResolver is a strategy interface to resolve method parameters in context of given context. So, if you want to automatically resolve the parameter MyObject in the following method, you can create a bean of HandlerMethodArgumentResolver and implement logic to resolve the argument.

public Page<User> getUsers(MyObject object) {

Spring Framework already provides a lot of resolvers to handle various parameters such as AuthenticationPrincipal, CSRF, Session, Cookie, MVC Model, and of course Pageable.


Pageable Resolver:

Spring Data comes with PageableHandlerMethodArgumentResolver to resolve pageable parameter from the request URL.

If you send a request /users?size=20&page=2, the Pageable object will be injected to the method parameter.

public Page<User> getUsers(Pageable pageable) {
return userRepository.findAllByStatus(Status.ACTIVE, pageable);

Customize PageableHandlerMethodArgumentResolver

To customize the Pageable resolver, we need to create a bean of PageableHandlerMethodArgumentResolverCustomizer , which will be applied at SpringDataWebConfiguration#customizePageableResolver before the pageableResolver() is created SpringDataWebConfiguration#pageableResolver.

PageableHandlerMethodArgumentResolverCustomizer is a SAM (single method interface aka FunctionalInterface). 

Setting max page size

public PageableHandlerMethodArgumentResolverCustomizer paginationCustomizer() {
return pageableResolver -> {
pageableResolver.setMaxPageSize(20); //default is 2000
pageableResolver.setPageParameterName("pageNumber"); //default is page
pageableResolver.setSizeParameterName("elementsPerPage"); //default is size

Now the url should be /users?elementsPerPage=20&pageNumber=2 instead of /users?size=20&page=2.

If you pass elementsPerPage more than 20, it will be defaulted back to 20.

Which will be helpful to prevent potential attacks trying to issue an OutOfMemoryError.