java - 线程 "main"java.lang.NoSuchFieldError : INSTANCE 中的异常

Question

我正在尝试使用 HTTPClient 编写一个简单的 WebService 测试。我已经加载了所有的 jar ，但收到了上述错误消息。

为什么我会收到此错误消息？

这是代码:

package HTTPClientTest;

import java.io.IOException;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.HttpClientBuilder;
import org.junit.Assert;


public class RESTTester {

    public static void main (String args[]) {

    String restURL_XML = "http://parabank.parasoft.com/parabank/services/bank/customers/12212/";


    try {

    testStatusCode(restURL_XML);

    } catch (ClientProtocolException e) {

    e.printStackTrace();
    } catch (IOException e) {
    e.printStackTrace();
    } 
}


public static void testStatusCode(String restURL) throws ClientProtocolException, IOException {
    HttpUriRequest request = new HttpGet(restURL);
    HttpResponse httpResponse = HttpClientBuilder.create().build().execute(request);
    Assert.assertEquals(httpResponse.getStatusLine().getStatusCode(),HttpStatus.SC_OK);
    }

}

下面是错误堆栈跟踪，

Exception in thread "main" java.lang.NoSuchFieldError: INSTANCE
    at org.apache.http.conn.ssl.SSLConnectionSocketFactory.<clinit>(SSLConnectionSocketFactory.java:144)
    at org.apache.http.impl.client.HttpClientBuilder.build(HttpClientBuilder.java:966)
    at HTTPClientTest.RESTTester.testStatusCode(RESTTester.java:37)
    at HTTPClientTest.RESTTester.main(RESTTester.java:22)

Answer 1

我收到上述错误是因为我的项目中有多个旧版本的 HTTPClient。我删除了旧版本的 HTTPClient，现在错误消息消失了。