JSON的JUnit Hamcrest Matcher

这篇文章展示了如何编写JUnit测试来检查对象是否与JSON字符串匹配。如果您要实现REST服务并想测试您的服务是否产生了预期的JSON响应，那么这一点很重要。

JSONassert是比较JSON对象的有用库。首先，您必须将Java对象转换为JSON字符串（例如，使用Jackson ），然后使用JSONassert将其与期望的JSON字符串进行比较。（您也可以将Java对象转换为JSONObject但我发现将其转换为字符串要容易得多。）

以下代码段显示了如何使用JSONassert将对象（在这种情况下为List ）与其JSON表示形式进行比较。

import org.skyscreamer.jsonassert.JSONAssert;
import com.fasterxml.jackson.databind.ObjectMapper;List<String> fruits = Arrays.asList("apple", "banana");
String fruitsJSON = new ObjectMapper().writeValueAsString(fruits);
String expectedFruitsJSON = "[\"apple\", \"banana\"]";
JSONAssert.assertEquals(expectedFruitsJSON, fruitsJSON, true);

为了简化编写这样的单元测试，我编写了一个名为IsEqualJSON的Hamcrest Matcher，用于比较JSON对象。它仍然使用JSONassert，但允许您以更流畅的方式表达测试。

以下代码显示了如何使用IsEqualJSON ：

import static org.junit.Assert.*;
import static testutil.IsEqualJSON.*;assertThat(Arrays.asList("apple", "banana"),equalToJSON("[\"apple\", \"banana\"]"));// you can also have your expected JSON read from a file
assertThat(Arrays.asList("apple", "banana"),equalToJSONInFile("fruits.json"));

这是IsEqualJSON的代码（也在我的GitHub Repository中提供）：

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.*;
import org.hamcrest.*;
import org.skyscreamer.jsonassert.*;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;/*** A Matcher for comparing JSON.* Example usage:* <pre>* assertThat(new String[] {"foo", "bar"}, equalToJSON("[\"foo\", \"bar\"]"));* assertThat(new String[] {"foo", "bar"}, equalToJSONInFile("/tmp/foo.json"));* </pre>*/
public class IsEqualJSON extends DiagnosingMatcher<Object> {private final String expectedJSON;private JSONCompareMode jsonCompareMode;public IsEqualJSON(final String expectedJSON) {this.expectedJSON = expectedJSON;this.jsonCompareMode = JSONCompareMode.STRICT;}@Overridepublic void describeTo(final Description description) {description.appendText(expectedJSON);}@Overrideprotected boolean matches(final Object actual,final Description mismatchDescription) {final String actualJSON = toJSONString(actual);final JSONCompareResult result = JSONCompare.compareJSON(expectedJSON,actualJSON,jsonCompareMode);if (!result.passed()) {mismatchDescription.appendText(result.getMessage());}return result.passed();}private static String toJSONString(final Object o) {try {return o instanceof String ?(String) o : new ObjectMapper().writeValueAsString(o);} catch (final JsonProcessingException e) {throw new RuntimeException(e);}}private static String getFileContents(final Path path) {try {return new String(Files.readAllBytes(path), StandardCharsets.UTF_8);} catch (final IOException e) {throw new RuntimeException(e);}}@Factorypublic static IsEqualJSON equalToJSON(final String expectedJSON) {return new IsEqualJSON(expectedJSON);}@Factorypublic static IsEqualJSON equalToJSONInFile(final Path expectedPath) {return equalToJSON(getFileContents(expectedPath));}@Factorypublic static IsEqualJSON equalToJSONInFile(final String expectedFileName) {return equalToJSONInFile(Paths.get(expectedFileName));}
}