Experiment with Embedded Solr in java and C

Solr is poster boy in search market . Generally it is used by running as HTTP server and making queries .
I was more interested in running it in embedded manner and getting results via JNI .

Following you will find the code for doing same and some problems you might face ( with solutions :) ) .

Getting the embedded solr working

    String solrDir = "/Users/TheRoot/Downloads/solr-4.7.0/example/solr/";
    container = new CoreContainer(solrDir);
    container.load();
    server = new EmbeddedSolrServer(container, "collection1");

This will get your basic EmbeddedSolr up and running .
Next if you want to make query and get response from the solr ; you can use the following function .

public static String query(String qstring){
    String output = null;
    ModifiableSolrParams solrParams = new ModifiableSolrParams();
    System.out.println(qstring);
    solrParams.add(CommonParams.Q, qstring);
    QueryResponse queryResponse = null;
    try {
        queryResponse = server.query(solrParams);
    } catch (SolrServerException e) {
        e.printStackTrace();
    }
    for (SolrDocument document : queryResponse.getResults()) {
        output += (document.getFieldValueMap().toString());
    }
    System.out.println(output);
    return output;
}

Similary we can update values , Index solr , query it etc ..
The other part of the experiment is getting C to talk to java via JNI .

First create a virtual java machine inside C

    JNIEnv* create_vm(JavaVM **jvm)
    {
        JNIEnv* env;
        JavaVMInitArgs args;
        JavaVMOption options;
        args.version = JNI_VERSION_1_6;
        args.nOptions = 1;
        options.optionString = "-Djava.class.path=/Users/TheRoot/Documents/workspac[...ALL REQUIRED JARS...]]7.0/dist/solrj-lib/noggit-0.5.jar";
        args.options = &options;
        args.ignoreUnrecognized = 0;
        int rv;
        rv = JNI_CreateJavaVM(jvm, (void**)&env, &args);
        if (rv < 0 || !env)
            printf("JVM launch failed%d\n",rv);
        else
            printf("Launched JVM\n");
        return env;
    }

Note : If you do not give path properly in options.optionStrings you will get error something similar to

    Invalid memory access of location 0x0 rip=0xADDR

Now call java function from C ..

EmbeddedSolrExample_Class = (*env)->FindClass(env, "EmbeddedSolrExample");

main_method = (*env)->GetStaticMethodID(env, EmbeddedSolrExample_Class, "main", "([Ljava/lang/String;)V");

(*env)->CallStaticVoidMethod(env, EmbeddedSolrExample_Class, main_method, NULL);  // Initialize the embedded solr 

One thing you might notice is 4th parameter “([Ljava/lang/String;)V” of GetStaticMethodID function . This is signature of any function in java , this has to be specific to the function input and return value , for example for the “main” function “([Ljava/lang/String;)V” is the signature . You can get this value easily using “javap” . Once you have made .class file from your .java file which you want to bind in c , run the following command :

    javap -s myclass.class

This will give output something like

    Compiled from "EmbeddedSolrExample.java"
    public class EmbeddedSolrExample extends java.lang.Object{
    static org.apache.solr.core.CoreContainer container;
      Signature: Lorg/apache/solr/core/CoreContainer;
    static org.apache.solr.client.solrj.embedded.EmbeddedSolrServer server;
      Signature: Lorg/apache/solr/client/solrj/embedded/EmbeddedSolrServer;
    public EmbeddedSolrExample();
      Signature: ()V
    public static void main(java.lang.String[])   throws java.lang.Exception;
      Signature: ([Ljava/lang/String;)V
    public static java.lang.String query(java.lang.String);
      Signature: (Ljava/lang/String;)Ljava/lang/String;
    public static void entervalues(java.lang.String, int, java.lang.String)   throws java.lang.Exception;
      Signature: (Ljava/lang/String;ILjava/lang/String;)V
    public static void close();
      Signature: ()V
    }

You can clearly see the signatures here .

Thats it , we now have an application with solr search embedded into it , without the need of running solr http server .

You can get the full code at

https://gist.github.com/nautical/9859418

https://gist.github.com/nautical/9859452

 
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