前几天写了个多线程通过HTTP下载文件的小程序，其中简单写了个HttpClient. 源码：GitHub

1 定义一个抽象BaseHttpMethod类

<pre>
`
public abstract class BaseHttpMethod {
protected static String HEAD = "HEAD";
protected static String GET = "GET";
protected static String POST = "POST";
String url;
protected Map paras = new HashMap();

protected abstract String getMethod();
protected abstract BaseBuilder getBuilder();
protected Map getParamters(){
    return paras;
}
public void putParamter(String key,Object value){
    paras.put(key, value);
}
protected void setUrl(String url) {
    this.url = url;
}
protected String getUrl(){
    return url;
}

protected BaseHttpMethod() {

}

protected BaseHttpMethod(String url) {
    this.url = url;
}

}
`
</pre>

下面定义了3个实现类：HttpGet，HttpPost，HttpHead

<pre>
`
public class HttpPost extends BaseHttpMethod {

@Override
public String getMethod() {
    return POST;
}

public HttpPost() {
}

public HttpPost(String url) {
    super(url);
}

@Override
protected BaseBuilder getBuilder() {
    return new PostConnectBuilder(this);
}

}
`
</pre>
其他2个HttpGet，HttpHead和这个差不多

2 定义一个Response 接口IHttpResponse

<pre>
`
public interface IHttpResponse {

public int getStatusCode() throws IOException;
public InputStream getInputStream() throws IOException;
public String getContent();
public Map<String, List<String>> getHeaders();
public String getHeader(String name);
public void close();

}
`
</pre>
HttpResponse简单实现了这个接口

<pre>
`
public class HttpResponse implements IHttpResponse {

private InputStream inputStream;
private HttpURLConnection con;

public HttpResponse(HttpURLConnection con) {
    this.con = con;
}

@Override
public int getStatusCode() throws IOException {

    return con != null ? con.getResponseCode() : -1;

}

@Override
public InputStream getInputStream() throws IOException {

    inputStream = null != con ? con.getInputStream() : null;

    return inputStream;
}

@Override
public String getContent() {
    if (inputStream != null) {
        StringBuffer content = new StringBuffer();
        BufferedInputStream bufferInputStream = new BufferedInputStream(
                inputStream);
        byte[] data = new byte[1024];
        int length;
        try {
            while ((length = bufferInputStream.read(data)) > 0) {
                content.append(new String(data, 0, length));
            }
            return content.toString();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    return null;
}

@Override
public Map<String, List<String>> getHeaders() {
    return null != con ? con.getHeaderFields() : null;
}

@Override
public String getHeader(String name) {
    return null != con ? con.getHeaderField(name) : null;
}

@Override
public void close() {
    if (null != null)
        con.disconnect();
}

}
`
</pre>

3 简单定义一个HttpClient

<pre>
`
public class HttpClient {
public static String HEAD = "HEAD";
public static String GET = "GET";
public static String POST = "POST";
private static HttpClient instance;
private HttpClient (){

}
public static HttpClient getInstance(){
    if(null == instance){
        synchronized (HttpClient .class) {
            instance =new HttpClient ();
        }
    }
    return instance;
}

public IHttpResponse exec(BaseHttpMethod method) throws IOException{
    return exec(method,null);
}
public IHttpResponse exec(BaseHttpMethod method,Map property) throws IOException{
    HttpURLConnection con = ConnectFactory.getInstance().getCon(method,property);
    return new HttpResponse(con);
}

}
`
</pre>

这里用到一个ConnectFactory 来获得URLHttpConnection

4 一个简单ConnectFactory

<pre>
`
public class ConnectFactory {
private static int CON_TIME_OUT = 5 * 100;
private static int READ_TIME_OUT = 10 * 1000;

public void setConnectTimeout(int connectTimeout) {
    CON_TIME_OUT = connectTimeout;
}

public void setReadTimeout(int readTimeout) {
    READ_TIME_OUT = readTimeout;
}

private static ConnectFactory instance;

private ConnectFactory() {

}

public static ConnectFactory getInstance() {
    if (null == instance) {
        synchronized (ConnectFactory.class) {
            instance = new ConnectFactory();
        }
    }
    return instance;
}

public HttpURLConnection getCon(BaseHttpMethod method,Map<String,String> property) throws IOException {

    HttpURLConnection con = method.getBuilder().build();
    
    con.setConnectTimeout(CON_TIME_OUT);
    con.setReadTimeout(READ_TIME_OUT);
    if(null != property && property.size()>0){
        Iterator keyIt = property.keySet().iterator();
        while(keyIt.hasNext()){
            String key = (String) keyIt.next();
            String value = property.get(key);
            con.setRequestProperty(key,value);
        }
    }
    //some sites will refuse, if no "User-Agent", so set default value
    if(property==null || !property.containsKey("User-Agent")){
        con.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0");
    }
    
    con.connect();
    method.getBuilder().doOutPut(con);
    return con;
}
public HttpURLConnection getCon(BaseHttpMethod method) throws IOException {
    return getCon(method, null);
}

}
</pre> 在这个工厂方法中用到了一个Builder, 其中的抽象类为： <pre>
public abstract class BaseBuilder {

protected BaseHttpMethod method;
public BaseBuilder(BaseHttpMethod method) {
    this.method=method;
}
protected void doOutPut(HttpURLConnection con){
    
}
protected abstract HttpURLConnection build() throws IOException;
protected String buildParamters(){
    Map paras = method.getParamters();
    StringBuffer sb = new StringBuffer();
    if(paras!=null && paras.size()>0){
        Iterator<String> keyIt = paras.keySet().iterator();
        while(keyIt.hasNext()){
            String key = keyIt.next();
            String value = (String) paras.get(key);
            String encodedValue = null;
            try {
                encodedValue = URLEncoder.encode(value, "UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            if(encodedValue!=null){
                sb.append(key).append("=").append(encodedValue);
            }else{
                sb.append(key).append("=").append(value);
            }
            if(keyIt.hasNext())sb.append("&");
        }
    }
    return sb.toString();
}

}
</pre> 其中的HeadConnectBuilder <pre>
public class HeadConnectBuilder extends BaseBuilder {

public HeadConnectBuilder(BaseHttpMethod method) {
    super(method);
}

@Override
protected HttpURLConnection build() throws IOException {
    String surl = method.getUrl();
    
    URL url = new URL(surl);
    HttpURLConnection con = (HttpURLConnection) url.openConnection();

    con.setRequestMethod(method.getMethod());

    return con;

}

}
`
</pre>

5 简单实用

<pre>
<code>
public static void main(String[] args) {

    BaseHttpMethod get = new HttpGet("http://www.jianshu.com");
    DownLoadHttpClient client = DownLoadHttpClient.getInstance();
    try {
        IHttpResponse response = client.exec(get);
        System.out.println(response.getContent());
    } catch (IOException e) {
        e.printStackTrace();
    }
    
}

</code>
</pre>
输出：
<!DOCTYPE html>




<html>

<head>

。。。。。。。

</html>