Tag Archives: java


Let me introduce you another of my pet projects. It’s called JsonUnit and it’s something like XmlUnit only for JSON (well it’s much, much more simple). Basically it’s able to compare two JSON documents and if they do not match, it prints out the differences. For example the following test

import static net.javacrumbs.jsonunit.JsonAssert.assertJsonEquals;


assertJsonEquals("{\n" + 
			"   \"test\":[\n" + 
			"      1,\n" + 
			"      2,\n" + 
			"      {\n" + 
			"         \"child\":{\n" + 
			"            \"value1\":1,\n" + 
			"            \"value2\":true,\n" + 
			"            \"value3\":\"test\",\n" + 
			"            \"value4\":{\n" + 
			"               \"leaf\":5\n" + 
			"            }\n" + 
			"         }\n" + 
			"      }\n" + 
			"   ],\n" + 
			"   \"root2\":false,\n" + 
			"   \"root3\":1\n" + 
			"{\n" + 
			"   \"test\":[\n" + 
			"      5,\n" + 
			"      false,\n" + 
			"      {\n" + 
			"         \"child\":{\n" + 
			"            \"value1\":5,\n" + 
			"            \"value2\":\"true\",\n" + 
			"            \"value3\":\"test\",\n" + 
			"            \"value4\":{\n" + 
			"               \"leaf2\":5\n" + 
			"            }\n" + 
			"         },\n" + 
			"         \"child2\":{\n" + 
			"\n" + 
			"         }\n" + 
			"      }\n" + 
			"   ],\n" + 
			"   \"root4\":\"bar\"\n" + 

will result in

java.lang.AssertionError: JSON documents are different:
Different keys found in node "". Expected [root2, root3, test], got [root4, test].
Different value found in node "test[0]". Expected 1, got 5.
Different types found in node "test[1]". Expected NUMBER, got BOOLEAN.
Different keys found in node "test[2]". Expected [child], got [child, child2].
Different value found in node "test[2].child.value1". Expected 1, got 5.
Different types found in node "test[2].child.value2". Expected BOOLEAN, got STRING.
Different keys found in node "test[2].child.value4". Expected [leaf], got [leaf2].

Neat, isn’t it?

Mock socket

Few months ago I have written a small tool that mocks network sockets in Java. Now I have some time to describe it, so here you are.

Let’s imagine you want to test network communication in Java. It’s not easy, you have to start some server on the other side, configure its responses and somehow verify that the data you send are correct.

With mock-socket it’s incredibly easy.

import static net.javacrumbs.mocksocket.MockSocket.*;

//prepare mock
byte[] dataToWrite = new byte[]{5,4,3,2};
//do test
Socket socket = SocketFactory.getDefault().createSocket("example.org", 1234);
IOUtils.write(dataToWrite, socket.getOutputStream());
//verify data sent
assertThat(recordedConnections().get(0), data(is(dataToWrite)));
assertThat(recordedConnections().get(0), address(is("example.org:1234")));

You see, just statically import MockSocket class, prepare the mock, execute the test and verify the data. The library just removes the default Java socket implementation and place a mock implementation in its stead.

Of course, this example does not have much sense. It just tests that Java socket implementation works. But imagine that you implement some non-trivial network library. A test library can be handy.

Moreover, there is a HTTP extension which can be used if you want to test some HTTP client. Let’s say a JSON REST client. In such case, you can write this.

import static net.javacrumbs.mocksocket.http.HttpMockSocket.*;


//prepare mock

//do your test

assertThat(recordedConnections(), hasItem(header("Accept", is("text/plain"))));		

Ain’t great? You can do much more, please take a look at the project page if you are interested.

Where does this class came from?

Today I have been debugging some nasty problem on Weblogic. The application worked on one version but did not work on an older one. Apparently some classes were not compatible. But it’s quite difficult to debug such problem. You need to find out from which JAR given class was taken from. It’s not trivial in enterprise environment. The class can be part of J2SE, application server and your EAR at the same time. Especially if the class has something to do with XML or web services. End if you have such class, you need some trick to determine which version was actually used.

The trick is simple yet not widely known. In fact I have encountered it in a Scala related article. You just call this code from JSP or some other suitable place.


And that’s all, this command will return path to your mystery class JAR.