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Using Jsoup library on eclipse [duplicate]

I have just recently started using Eclipse and am running into problems trying to install external libraries. Following online tutorials, I add the .jar file to the classpath and I see it in the referenced libraries folder. Despite this, when trying to import, I get the error:
The package org.apache.commons is not accessible
For reference, I am trying to install the apache math commons library.

Your code probably has two issues.
First, the import statement is wrong since in Java you cannot add a package itself, but all classes of a package as follows (note .*; at the end):
import org.apache.commons.math4.linear.*;
or a specific class, e.g.
import org.apache.commons.math4.linear.FieldMatrix;
Second, you use the Java Platform Module System (JPMS) by having a module-info.java file in the default package probably without the required requires <module>; statement. JPMS was introduced in Java 9 and you have Java 12.
Do one of the following:
Delete the module-info.java file (if needed, you can recreate it via right-clicking the project folder and choosing Configure > Create module-info.java)
In module-info.java add the corresponding requires statement, e.g. by going to the line with the import statement and using the corresponding Quick Fix (Ctrl+1)

Importing FlatBuffers libraries and generated source into Android Studio Project

We are evaluating FlatBuffers as a potential solution for packing and unpacking various data payloads. I have built flatc.exe, constructed schemas for our data, and generated Java code from the schemas. I am now trying to use the generated code.
This overview states:
Then you can include both FlatBuffers and the generated code to read or write a FlatBuffer.
And does so as follows in the example:
import MyGame.Example.*;
import com.google.flatbuffers.FlatBufferBuilder;
1) Should the generated code be imported as a new module/Java Library, dependency, or something else? How is this done?
2) The import of com.google.flatbuffers.FlatBufferBuilder also does not resolve. Anyone know if this reference has changed?
Appreciate any help you can provide to an Android neophyte on how to import these items.
Thanks.

FlatBuffers doesn't come with integrations for any specific IDE's or package managers (which is something we should fix). For now the easiest is to copy the contents of FlatBuffers java/ folder to where-ever you keep your project's Java code, along with the generated code (in its package directory).

problems building the protobuf example apps

I'm new to protobufs and was trying to learn more about using them. I've downloaded the protobuf packaged from here. There is a README.txt file inside the examples folder of the archive which gives instructions on how to build 2 example applications. However when I follow those instructions for building the java application:
make java
I get a lot of errors followed by:
100 errors
make: * [javac_middleman] Error 1
All of the 100 errors seem to be classpath related, as this is a typical example:
com/example/tutorial/AddressBookProtos.java:37: error: package com.google.protobuf does not exist
Any ideas about how to get passed this?

The problem is that for some reason protobuf jar is not added to the classpath during compilation. To fix it you should open examples/Makefile and add -cp protobuf-java-2.4.1.jar at the end of java complilation line javac AddPerson.java ListPeople.java com/example/tutorial/AddressBookProtos.java.
P.S. If you built you protobufs with maven the jar is located at ~/.m2/repository/com/google/protobuf/protobuf-java/2.4.1/protobuf-java-2.4.1.jar (version of the jar might be different)

Imported jar files creates empty packages

I am importing a Jar file "com.ibm.mq.jar" into my workspace(Eclipse IDE).
While importing, a screen came where I could see all the classes in the Jar file.
After I imported it into the work space, I was able to import the package and following statement didn't give any error.
import com.ibm.mq.*;
But, in code I am not able to use any of the classes which were there in the package.
Like, "MQC" is a class in the package, but in code it doesn't reflect("MQC cannot be resolved as a type" error comes if I try to use it).
This jar file actually contains Websphere MQ API classes.
Can anyone advise, what am I missing.

If you're using MQ 7, check its documentation here. There was some stuff going on about deprecation of com.ibm.mq.mqc and, depending on the version you use, that class was replaced by com.ibm.mq.constants.MQConstants. Like this one, there are other cases.
In fact com.ibm.mq only contains the exception MQException, so you won't find any classes there. I suggest you check the version you're using and dig a little deeper into the docs, as a first step.

Using MessagePack with Android

Has someone tried to use MessagePack with an Android app?
Is it possible? I have tried to use the Jar from msgpack-java and received the following Exception:
Caused by: java.lang.ExceptionInInitializerError
at org.msgpack.Packer.pack(Packer.java:532)
at org.msgpack.MessagePack.pack(MessagePack.java:31)
... 15 more
Caused by: java.lang.ExceptionInInitializerError
at org.msgpack.template.TemplateRegistry.<clinit>(TemplateRegistry.java:38)
... 17 more
Caused by: java.lang.VerifyError: org.msgpack.template.BeansFieldEntryReader
at org.msgpack.template.builder.BeansTemplateBuilder.<init (BeansTemplateBuilder.java:42)
at org.msgpack.template.builder.BuilderSelectorRegistry.initForJava(BuilderSelectorRegistry.java:73)
at org.msgpack.template.builder.BuilderSelectorRegistry.<clinit>(BuilderSelectorRegistry.java:38)
... 18 more
The code that I use is very simple
PrintWriter out = new PrintWriter(socket.getOutputStream());
Message msg = new Message();
msg.body = "asdasdasd";
msg.from = "qwe";
msg.to = "ttt";
byte[] bytes = MessagePack.pack(msg);
out.print(bytes);
out.flush();
I have javassist.jar, msgpack-0.5.2.jar, slf4j-api-1.6.2.jar and slf4j-jdk14-1.6.2.jar in my lib directory.
In my server application this code works fine with the same libraries.

(Hopefully) FINAL UPDATE
msgpack : 0.6.8 works on Android without any problems
msgpack-rpc : 0.7.0 works on Android with one caveat.
Specifically, you need to add the following to onCreate for API Level 8 (Android 2.2.1), and possibly lower:
java.lang.System.setProperty("java.net.preferIPv4Stack", "true");
java.lang.System.setProperty("java.net.preferIPv6Addresses", "false");
due to this bug.
If you want to see a simple example, here's a pair of projects set up for this purpose:
https://github.com/mikkoz/msgpack-android-test-server/tree/master/msgpack-android-test-server
https://github.com/mikkoz/msgpack-android-test-client/tree/master/msgpack-android-test-client
Previous Versions
UPDATE: as of 0.6.7 msgpack should be compatible with Android (there is a small dependency exclusion issue). Check the text below for msgpack-rpc (which also might be adapted in the future).
NOTE: If you're also using msgpack-rpc, you need to do the following steps:
Download the msgpack-rpc source from git://github.com/msgpack/msgpack-rpc.git (specifically, the "java" folder).
Change the main msgpack artifact version to the one you've built.
In org.msgpack.rpc.loop.netty.NettyEventLoop, change the NioClientSocketChannelFactory to OioClientSocketChannelFactory(getWorkerExecutor()).
Build the MessagePack-RPC in the same way as in the case of the main MessagePack JAR (see Step 11 above).
The NettyEventLoop replacement is due to this issue:
http://markmail.org/message/ypa3nrr64kzsyfsa .
Important: I've only tested synchronous communication. Asynchronous might not work.
And here's the reason for msgpack not working with Android prior to 0.6.7:
The reason for the error is that MessagePack uses several java.beans classes that are not included in the Android SDK. You're probably using the MessagePackBeans annotation.
This is a similar problem to the one described here, for which the general solution is outlined here. Unfortunately, in our case it requires a rebuild of msgpack. Here's what I did (you can almost certainly skip Steps 5 and 8, but I haven't tried it that way) :
Download the MessagePack source from https://github.com/msgpack/msgpack-java.git.
Import the MessagePack source as a project in your IDE.
Download the Apache Harmony source for the relevant packages from http://svn.apache.org/repos/asf/harmony/enhanced/java/trunk/classlib/modules/beans/src/main/java .
Copy these packages into your MessagePack project's src/main/java folder:
java.beans
java.beans.beancontext
org.apache.harmony.beans
org.apache.harmony.beans.internal.nls
In your MessagePack project, remove the following classes:
PropertyChangeListener
IndexedPropertyChangeEvent
PropertyChangeEvent
PropertyChangeListenerProxy
PropertyChangeSupport
Rename the java.beans packages to something different, e.g. custom.beans .
Change all java.beans references to the renamed ID, so again e.g. custom.beans. This applies especially to BeansFieldEntryReader (this class is the reason for the original error).
Change the custom.beans references for the five classes you removed in Step 5 back to java.beans.
In the org.apache.harmony.beans.internal.nls.Messages class, comment out the method setLocale, and remove the imports associated with it.
Remove all classes that still have errors, except Encoder. In that class, comment out all references to the classes you've removed. You should now have an error-free project.
Build the MessagePack JAR:
If you're using Maven, change the version in the pom.xml to something unique, run Maven build with the install goal, then add the dependency in your Android project with that version.
If you're not using Maven, you have to run the jar goal for Ant with the included build.xml. Replace the msgpack JAR in your Android project with this one.
If you're publishing your app, remember to include the relevant legal notice for Apache Harmony. It's an Apache License, just like MessagePack.
That should do it. Using your example code, and my own data class, I was successfully able to pack and unpack data.
The entire renaming ritual is due to the fact that the DEX compiler complains about java.* package naming.

There is a critical msgpack bug saying data packed with msgpack will get corrupted on the Dalvik VM. http://jira.msgpack.org/browse/MSGPACK-51

There is an ongoing effort by #TheTerribleSwiftTomato and the MessagePack core team to get MessagePack working on Android, please see the related GitHub issue. The fix mentioned in #TheTerribleSwiftTomato's answer is to be found here.
Update
I've managed to get it at least running on Android by (painstakingly) adding all the necessary javassist Classes which are currently required for the build to succeed. An extra 600KB gain in size, yet at least it seems to work. All in all, it appears to be working to some extent on Android, eventually check out the lesser-known resources about Message Pack such as its User Group and its Wiki for more information.
On a side-note, be sure to use a HTTP Request Library (such as LoopJ's Android Async HTTP or Apache's HttpClient) which can handle binary data.
Last but not least you can ping me if there is interest in this jar which makes MessagePack seemingly work on Android – credits go out of course to #TheTerribleSwiftTomato who supplied the fix above!

I suggest you write this in the main proguard-rules file-
-dontwarn org.msgpack.**
-keep class org.msgpack.** { *; }