httpClient4.5（一、基础篇）

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我们经常会遇到与第三方系统之间进行网络交互，此时通常会使用httpClient来访问第三方系统提供的接口进行相应的交互。

一、httpClient简介：

HttpClient 是 Apache Jakarta Common 下的子项目，可以用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。

使用HttpClient发送请求、接收响应很简单，一般需要如下几步即可：
1.创建CloseableHttpClient对象。
2.创建请求方法的实例，并指定请求URL。如果需要发送GET请求，创建HttpGet对象；如果需要发送POST请求，创建HttpPost对象。
3.如果需要发送请求参数，可调用setEntity(HttpEntity entity)方法来设置请求参数。
4.调用HttpGet、HttpPost对象的setHeader(String name, String value)方法设置header信息，或者调用setHeaders(Header[] headers)设置一组header信息。
5.调用CloseableHttpClient对象的execute(HttpUriRequest request)发送请求，该方法返回一个CloseableHttpResponse。
6.调用HttpResponse的getEntity()方法可获取HttpEntity对象，该对象包装了服务器的响应内容。程序可通过该对象获取服务器的响应内容；调用CloseableHttpResponse的getAllHeaders()、getHeaders(String name)等方法可获取服务器的响应头。
7.释放连接。无论执行方法是否成功，都必须释放连接

二、maven依赖（pom.xml）：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>com.http.demo</groupId>
	<artifactId>http</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>http</name>
	<url>http://maven.apache.org</url>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
		<httpcore.version>4.4.6</httpcore.version>
		<httpclient.version>4.5.5</httpclient.version>
		<slf4j.version>1.7.25</slf4j.version>
		<fastjson.version>1.2.47</fastjson.version>
	</properties>
	
	<dependencies>
		<!-- http client -->
		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpclient</artifactId>
			<version>${httpclient.version}</version>
		</dependency>

		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpcore</artifactId>
			<version>${httpcore.version}</version>
		</dependency>

		<dependency>
			<groupId>org.apache.httpcomponents</groupId>
			<artifactId>httpmime</artifactId>
			<version>${httpclient.version}</version>
		</dependency>

		<!-- slf4j -->
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-api</artifactId>
			<version>${slf4j.version}</version>
		</dependency>

		<!-- fastjson -->
		<dependency>
			<groupId>com.alibaba</groupId>
			<artifactId>fastjson</artifactId>
			<version>${fastjson.version}</version>
		</dependency>
		
		<dependency>
			<groupId>org.apache.commons</groupId>
			<artifactId>commons-lang3</artifactId>
			<version>3.1</version>
		</dependency>
	</dependencies>

	<!-- jdk1.7 -->
	<build>
		<finalName>${project.artifactId}-${project.version}</finalName>
		<plugins>
			<plugin>
				<groupId>org.apache.maven.plugins</groupId>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.1</version>
				<configuration>
					<source>1.7</source>
					<target>1.7</target>
				</configuration>
			</plugin>
		</plugins>
	</build>

</project>

三、httpClient编程

• get请求

1、参数直接拼接到URL后面，即http://test.com?a=1&b=2的形式

/**
     * get请求，参数拼接在地址上
     * @param url 请求地址加参数
     * @return 响应
     */
    public String get(String url)
    {
        String result = null;
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet get = new HttpGet(url);
        CloseableHttpResponse response = null;
        try {
            response = httpClient.execute(get);
            if(response != null && response.getStatusLine().getStatusCode() == 200)
            {
                HttpEntity entity = response.getEntity();
                result = entityToString(entity);
            }
            return result;
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                httpClient.close();
                if(response != null)
                {
                    response.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

2、参数放置到一个map中

/**
     * get请求，参数放在map里
     * @param url 请求地址
     * @param map 参数map
     * @return 响应
     */
    public String getMap(String url,Map<String,String> map)
    {
        String result = null;
        CloseableHttpClient httpClient = HttpClients.createDefault();
        List<NameValuePair> pairs = new ArrayList<NameValuePair>();
        for(Map.Entry<String,String> entry : map.entrySet())
        {
            pairs.add(new BasicNameValuePair(entry.getKey(),entry.getValue()));
        }
        CloseableHttpResponse response = null;
        try {
            URIBuilder builder = new URIBuilder(url);
            builder.setParameters(pairs);
            HttpGet get = new HttpGet(builder.build());
            response = httpClient.execute(get);
            if(response != null && response.getStatusLine().getStatusCode() == 200)
            {
                HttpEntity entity = response.getEntity();
                result = entityToString(entity);
            }
            return result;
        } catch (URISyntaxException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                httpClient.close();
                if(response != null)
                {
                    response.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return null;
    }

• POST请求：

1、参数放到map中

/**
     * 发送post请求，参数用map接收
     * @param url 地址
     * @param map 参数
     * @return 返回值
     */
    public String postMap(String url,Map<String,String> map) {
        String result = null;
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost post = new HttpPost(url);
        List<NameValuePair> pairs = new ArrayList<NameValuePair>();
        for(Map.Entry<String,String> entry : map.entrySet())
        {
            pairs.add(new BasicNameValuePair(entry.getKey(),entry.getValue()));
        }
        CloseableHttpResponse response = null;
        try {
            post.setEntity(new UrlEncodedFormEntity(pairs,"UTF-8"));
            response = httpClient.execute(post);
            if(response != null && response.getStatusLine().getStatusCode() == 200)
            {
                HttpEntity entity = response.getEntity();
                result = entityToString(entity);
            }
            return result;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                httpClient.close();
                if(response != null)
                {
                    response.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

        }
        return null;
    }

2、参数是json字符串

/**
     * post请求，参数为json字符串
     * @param url 请求地址
     * @param jsonString json字符串
     * @return 响应
     */
    public String postJson(String url,String jsonString)
    {
        String result = null;
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost post = new HttpPost(url);
        CloseableHttpResponse response = null;
        try {
            post.setEntity(new ByteArrayEntity(jsonString.getBytes("UTF-8")));
            response = httpClient.execute(post);
            if(response != null && response.getStatusLine().getStatusCode() == 200)
            {
                HttpEntity entity = response.getEntity();
                result = entityToString(entity);
            }
            return result;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                httpClient.close();
                if(response != null)
                {
                    response.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

entityToString方法：

private String entityToString(HttpEntity entity) throws IOException {
        String result = null;
        if(entity != null)
        {
            long lenth = entity.getContentLength();
            if(lenth != -1 && lenth < 2048)
            {
                result = EntityUtils.toString(entity,"UTF-8");
            }else {
                InputStreamReader reader1 = new InputStreamReader(entity.getContent(), "UTF-8");
                CharArrayBuffer buffer = new CharArrayBuffer(2048);
                char[] tmp = new char[1024];
                int l;
                while((l = reader1.read(tmp)) != -1) {
                    buffer.append(tmp, 0, l);
                }
                result = buffer.toString();
            }
        }
        return result;
    }