Apache HttpClient in MATLAB 2012+

Question

I want to use the apache httpclient for interaction with webservices. Specifically I'm using http://mirror.arcor-online.net/www.apache.org//httpcomponents/httpclient/binary/httpcomponents-client-4.3-bin.zip

So in MATLAB I'm loading all the included jars into the javaclasspath and then I can create to client-instance to work with:

In MATLAB 2007b and 2011b (those are the versions I have):

client = org.apache.http.impl.client.HttpClients.createDefault()
client =

org.apache.http.impl.client.InternalHttpClient@1e89831

In 2012b:

>> client = org.apache.http.impl.client.HttpClients.createDefault()

Java exception occurred:
java.lang.NoSuchFieldError: INSTANCE

    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:52)

    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<init>(DefaultHttpRequestWriterFactory.java:56)

    at org.apache.http.impl.io.DefaultHttpRequestWriterFactory.<clinit>(DefaultHttpRequestWriterFactory.java:46)

    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:72)

    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<init>(ManagedHttpClientConnectionFactory.java:84)

    at org.apache.http.impl.conn.ManagedHttpClientConnectionFactory.<clinit>(ManagedHttpClientConnectionFactory.java:59)

    at
    org.apache.http.impl.conn.PoolingHttpClientConnectionManager$InternalConnectionFactory.<init>(PoolingHttpClientConnectionManager.java:487)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:147)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:136)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:112)

    at org.apache.http.impl.client.HttpClientBuilder.build(HttpClientBuilder.java:710)

    at org.apache.http.impl.client.HttpClients.createDefault(HttpClients.java:58)


>> client = org.apache.http.impl.client.HttpClients.createDefault()
Java exception occurred:
java.lang.NoClassDefFoundError: Could not initialize class org.apache.http.impl.conn.ManagedHttpClientConnectionFactory

    at
    org.apache.http.impl.conn.PoolingHttpClientConnectionManager$InternalConnectionFactory.<init>(PoolingHttpClientConnectionManager.java:487)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:147)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:136)

    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.<init>(PoolingHttpClientConnectionManager.java:112)

    at org.apache.http.impl.client.HttpClientBuilder.build(HttpClientBuilder.java:710)

    at org.apache.http.impl.client.HttpClients.createDefault(HttpClients.java:58)

This is really bugging me, since code in 2011b and 2012b is identical, all jar's are loaded, and both Java-Versions coming with MATLAB are identical as well (1.6.0_17-b04). So I really don't get why classes have become unloadable in 2012b.

I tried playing around with the matlab classloader - but this confuses me even more:

>> jloader =  com.mathworks.jmi.ClassLoaderManager.getClassLoaderManager();
>> jloader.loadClass('org.apache.http.impl.conn.ManagedHttpClientConnectionFactory')
Java exception occurred:
java.lang.NoClassDefFoundError: Could not initialize class org.apache.http.impl.conn.ManagedHttpClientConnectionFactory

    at java.lang.Class.forName0(Native Method)

    at java.lang.Class.forName(Unknown Source)

    at com.mathworks.jmi.ClassLoaderManager.loadClass(ClassLoaderManager.java:440)


>> jloader.getCurrentClassLoader.loadClass('org.apache.http.impl.conn.ManagedHttpClientConnectionFactory')

ans =

class org.apache.http.impl.conn.ManagedHttpClientConnectionFactory

I also tried putting all jar-files onto the static classpath - which didn't have any effect either. Glad about any ideas on how solve this or how find the actual reason for the issue...

Answer 1

You have mismatched versions of httpclient and httpcore on your classpath. It appears that you have upgraded only httpclient but none of its dependencies. You can see a dependency list on the Apache HttpClient project page. http://hc.apache.org/httpcomponents-client-4.3.x/httpclient/dependencies.html

You should also make sure you don't have multiple versions of dependencies on the classpath. It seems like MATLAB 2012b already has a version of httpcore which is why you're encountering this conflict.