Java の HttpClient の使い方 (Post)

次のページを参考にしました。
[Java HTTP通信のサンプル(HttpClient)](https://itsakura.com/java-httpclient)

Ubuntu 21.04 で確認しました。

```java:Http_post.java
// -----------------------------------------------------------------------
/*
	Http_post.java

				Jul/30/2020
*/
// -----------------------------------------------------------------------
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpStatus;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

// -----------------------------------------------------------------------
class Uri_get {

	static String uri_post_proc(String uri,List<NameValuePair> params)
		{
		String res = "";

		Charset charset = StandardCharsets.UTF_8;

		CloseableHttpClient httpclient = HttpClients.createDefault();
		
		HttpPost request = new HttpPost(uri);

		System.out.println
			("requestの実行　「" + request.getRequestLine() + "」");
		
		CloseableHttpResponse response = null;

		try {
			request.setEntity(new UrlEncodedFormEntity(params));
			response = httpclient.execute(request);
			
			int status = response.getStatusLine().getStatusCode();
			System.out.println("HTTPステータス:" + status);
			//HTTPステータス:200
			
			if (status == HttpStatus.SC_OK){
				
				res = EntityUtils.toString(response.getEntity(),charset);
			}
		} catch (ClientProtocolException e) {
			e.printStackTrace();
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				if (response != null) {
					response.close();
				}
				if (httpclient != null) {
					httpclient.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

	return res;
	}
}

// -----------------------------------------------------------------------
public class Http_post
{
	public static void main(String[] args)
	{
	String uri = "https://httpbin.org/post";		
	List<NameValuePair> params = new ArrayList<>();
	params.add(new BasicNameValuePair("user","jiro"));
	params.add(new BasicNameValuePair("password","123456"));
		
	String res = Uri_get.uri_post_proc(uri,params);
	System.out.println(res);
	}
}

// -----------------------------------------------------------------------
```

```text:Makefile
LIB=/usr/share/java
HTTPCLIENT_JAR=.:$(LIB)/httpclient-4.5.13.jar:$(LIB)/httpcore-4.4.14.jar
Http_post.class: Http_post.java
	javac -cp $(HTTPCLIENT_JAR) Http_post.java
clean:
	rm -f *.class
```

実行コマンド

```bash
LIB=/usr/share/java
HTTPCLIENT_JAR=.:$LIB/httpclient-4.5.13.jar:$LIB/httpcore-4.4.14.jar:$LIB/commons-logging-1.2.jar
#
java -cp $HTTPCLIENT_JAR Http_post
```

実行結果

```text
equestの実行　「POST https://httpbin.org/post HTTP/1.1」
HTTPステータス:200
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "password": "123456", 
    "user": "jiro"
  }, 
  "headers": {
    "Accept-Encoding": "gzip,deflate", 
    "Content-Length": "25", 
    "Content-Type": "application/x-www-form-urlencoded", 
    "Host": "httpbin.org", 
    "User-Agent": "Apache-HttpClient/4.5.13 (Java/11.0.11)", 
    "X-Amzn-Trace-Id": "Root=1-5f227120-343daab017c55220a4835cd0"
  }, 
  "json": null, 
  "origin": "219.126.139.62", 
  "url": "https://httpbin.org/post"
}

```

同じことを curl で実行すると

```text
$ curl -X POST https://httpbin.org/post -d 'user=jiro&password=123456'
{
  "args": {}, 
  "data": "", 
  "files": {}, 
  "form": {
    "password": "123456", 
    "user": "jiro"
  }, 
  "headers": {
    "Accept": "*/*", 
    "Content-Length": "25", 
    "Content-Type": "application/x-www-form-urlencoded", 
    "Host": "httpbin.org", 
    "User-Agent": "curl/7.68.0", 
    "X-Amzn-Trace-Id": "Root=1-5f227156-cc1deef43116e768265ffeb8"
  }, 
  "json": null, 
  "origin": "219.126.139.62", 
  "url": "https://httpbin.org/post"
}
```

Get のサンプルはこちらです。
[Java の HttpClient の使い方 (Get)](https://qiita.com/ekzemplaro/items/0d23455c9930caa4c069)