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Add Filter to Extract Http Headers and Write them as Log Fields
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‎cf-java-logging-support-servlet/src/main/java/com/sap/hcp/cf/logging/servlet/filter/AddHttpHeadersToLogContextFilter.java‎

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package com.sap.hcp.cf.logging.servlet.filter;
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import static java.util.Collections.unmodifiableList;
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import static java.util.stream.Collectors.toList;
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import java.util.Arrays;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Stream;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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import com.sap.hcp.cf.logging.common.LogContext;
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import com.sap.hcp.cf.logging.common.request.HttpHeader;
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import com.sap.hcp.cf.logging.common.request.HttpHeaders;
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/**
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* Extracts the HTTP headers from the request and adds them to the logging
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* context. It defaults to {@link HttpHeaders#propagated()}. Custom headers can
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* be used.
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*/
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public class AddHttpHeadersToLogContextFilter extends AbstractLoggingFilter {
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private List<HttpHeader> headers;
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private List<String> fields;
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/**
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* The default constructor uses {@link HttpHeaders#propagated()} to define
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* the HTTP headers, that are added to the logging context.
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*/
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public AddHttpHeadersToLogContextFilter() {
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this(HttpHeaders.propagated());
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}
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public AddHttpHeadersToLogContextFilter(HttpHeader... headers) {
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this(Collections.emptyList(), headers);
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}
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/**
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* Use this constructor to add your own HTTP headers to the default list.
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* You need to implement {@link HttpHeader}. Note, that
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* {@link HttpHeader#isPropagated} needs to be true. All other headers will
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* be ignored. Usage to add your own header would be:
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* {@code new AddHttpHeadersToLogContextFilter(HttpHeaders.propagated, yourHeader)}
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*
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* @param list
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* a list of {@link HttpHeader}, can be default
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* {@link HttpHeaders#propagated()}
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* @param custom
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* a single {@link HttpHeader} to add to the list
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*/
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public AddHttpHeadersToLogContextFilter(List<? extends HttpHeader> list, HttpHeader... custom) {
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Stream<HttpHeader> allHeaders = Stream.concat(list.stream(), Arrays.stream(custom));
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this.headers = unmodifiableList(allHeaders.filter(HttpHeader::isPropagated).collect(toList()));
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this.fields = unmodifiableList(headers.stream().map(HttpHeader::getField).filter(f -> f != null).collect(
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toList()));
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}
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@Override
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protected void preProcess(HttpServletRequest request, HttpServletResponse response) {
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for (HttpHeader header: headers) {
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String headerValue = HttpHeaderUtilities.getHeaderValue(request, header);
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if (header.getField() != null && headerValue != null) {
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LogContext.add(header.getField(), headerValue);
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}
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}
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}
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@Override
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protected void postProcess(HttpServletRequest request, HttpServletResponse response) {
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fields.forEach(LogContext::remove);
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}
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}

‎cf-java-logging-support-servlet/src/test/java/com/sap/hcp/cf/logging/servlet/filter/AddHttpHeadersToLogContextFilterTest.java‎

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package com.sap.hcp.cf.logging.servlet.filter;
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import static org.hamcrest.MatcherAssert.assertThat;
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import static org.hamcrest.Matchers.any;
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import static org.hamcrest.Matchers.containsInAnyOrder;
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import static org.hamcrest.Matchers.either;
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import static org.hamcrest.Matchers.equalTo;
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import static org.hamcrest.Matchers.hasEntry;
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import static org.hamcrest.Matchers.is;
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import static org.hamcrest.Matchers.not;
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import static org.hamcrest.Matchers.nullValue;
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import static org.mockito.Mockito.doAnswer;
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import static org.mockito.Mockito.when;
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import java.util.stream.Stream;
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import javax.servlet.FilterChain;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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import org.junit.Before;
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import org.junit.Test;
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import org.junit.runner.RunWith;
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import org.mockito.Mock;
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import org.mockito.runners.MockitoJUnitRunner;
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import org.slf4j.MDC;
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import com.sap.hcp.cf.logging.common.request.HttpHeader;
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import com.sap.hcp.cf.logging.common.request.HttpHeaders;
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@RunWith(MockitoJUnitRunner.class)
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public class AddHttpHeadersToLogContextFilterTest {
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@Mock
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private HttpServletRequest request;
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@Mock
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private HttpServletResponse response;
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@Mock
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private FilterChain chain;
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private ContextMapExtractor mdcExtractor;
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@Before
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public void setUp() throws Exception {
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MDC.clear();
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mdcExtractor = new ContextMapExtractor();
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doAnswer(mdcExtractor).when(chain).doFilter(request, response);
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}
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@Test
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public void addsSingleHttpHeader() throws Exception {
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when(request.getHeader("my-header")).thenReturn("my-value");
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HttpTestHeader myHeader = new HttpTestHeader("my-header", "my-field", null, true);
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new AddHttpHeadersToLogContextFilter(myHeader).doFilter(request, response, chain);
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assertThat(mdcExtractor.getField("my-field"), is(equalTo("my-value")));
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}
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@Test
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public void ignoresNotPropagatedHttpHeader() throws Exception {
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when(request.getHeader("my-header")).thenReturn("my-value");
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HttpTestHeader myHeader = new HttpTestHeader("my-header", "my-field", null, false);
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new AddHttpHeadersToLogContextFilter(myHeader).doFilter(request, response, chain);
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assertThat(mdcExtractor.getContextMap(), is(nullValue()));
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}
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@Test
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public void ignoresHttpHeadersWithoutField() throws Exception {
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when(request.getHeader("my-header")).thenReturn("my-value");
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HttpTestHeader myHeader = new HttpTestHeader("my-header", null, null, true);
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new AddHttpHeadersToLogContextFilter(myHeader).doFilter(request, response, chain);
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assertThat(mdcExtractor.getContextMap(), is(nullValue()));
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}
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@Test
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public void ignoresMissingHeaderValues() throws Exception {
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HttpTestHeader myHeader = new HttpTestHeader("my-header", "my-field", null, true);
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new AddHttpHeadersToLogContextFilter(myHeader).doFilter(request, response, chain);
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assertThat(mdcExtractor.getContextMap(), is(nullValue()));
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}
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@Test
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public void removesFieldAfterFiltering() throws Exception {
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when(request.getHeader("my-header")).thenReturn("my-value");
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HttpTestHeader myHeader = new HttpTestHeader("my-header", "my-field", null, true);
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new AddHttpHeadersToLogContextFilter(myHeader).doFilter(request, response, chain);
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assertThat(MDC.getCopyOfContextMap(), either(not(hasEntry(any(String.class), any(String.class)))).or(is(nullValue())));
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}
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@Test
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public void addsDefaultFields() throws Exception {
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streamDefaultHeaders().map(HttpHeader::getName).forEach(n -> when(request.getHeader(n)).thenReturn(n + "-test_value"));
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new AddHttpHeadersToLogContextFilter().doFilter(request, response, chain);
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String[] fields = streamDefaultHeaders().map(HttpHeader::getField).toArray(String[]::new);
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assertThat(mdcExtractor.getContextMap().keySet(), containsInAnyOrder(fields));
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}
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private Stream<HttpHeaders> streamDefaultHeaders() {
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return HttpHeaders.propagated().stream();
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}
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}

‎cf-java-logging-support-servlet/src/test/java/com/sap/hcp/cf/logging/servlet/filter/ContextMapExtractor.java‎

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package com.sap.hcp.cf.logging.servlet.filter;
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import java.util.Map;
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import org.mockito.invocation.InvocationOnMock;
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import org.mockito.stubbing.Answer;
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import org.slf4j.MDC;
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public class ContextMapExtractor implements Answer<Void> {
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private Map<String, String> contextMap;
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public Map<String, String> getContextMap() {
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return contextMap;
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}
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public String getField(String name) {
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return contextMap.get(name);
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}
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@Override
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public Void answer(InvocationOnMock invocation) throws Throwable {
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contextMap = MDC.getCopyOfContextMap();
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return null;
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}
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}

‎cf-java-logging-support-servlet/src/test/java/com/sap/hcp/cf/logging/servlet/filter/CorrelationIdFilterTest.java‎

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@@ -10,8 +10,6 @@
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import static org.mockito.Mockito.verifyNoMoreInteractions;
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import static org.mockito.Mockito.when;
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import java.util.Collections;
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import java.util.List;
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import java.util.UUID;
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import javax.servlet.FilterChain;
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import org.junit.Test;
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import org.junit.runner.RunWith;
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import org.mockito.Mock;
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import org.mockito.invocation.InvocationOnMock;
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import org.mockito.runners.MockitoJUnitRunner;
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import org.mockito.stubbing.Answer;
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import org.slf4j.MDC;
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3026
import com.sap.hcp.cf.logging.common.request.HttpHeader;
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@Mock
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private FilterChain chain;
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45-
private CorrelationIdFromMDCExtractor mdcExtractor;
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private ContextMapExtractor mdcExtractor;
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4743
@Before
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public void setUp() throws Exception {
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mdcExtractor = new CorrelationIdFromMDCExtractor(HttpHeaders.CORRELATION_ID.getField());
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MDC.clear();
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mdcExtractor = new ContextMapExtractor();
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doAnswer(mdcExtractor).when(chain).doFilter(request, response);
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}
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public String getExtractedCorrelationId() {
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return mdcExtractor.getField(HttpHeaders.CORRELATION_ID.getField());
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}
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5354
@Test
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public void addsKnownCorrelationIdToMDC() throws Exception {
5556
when(request.getHeader(HttpHeaders.CORRELATION_ID.getName())).thenReturn(KNOWN_CORRELATION_ID);
5657

5758
new CorrelationIdFilter().doFilter(request, response, chain);
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59-
assertThat(mdcExtractor.getCorrelationId(), is(equalTo(KNOWN_CORRELATION_ID)));
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assertThat(getExtractedCorrelationId(), is(equalTo(KNOWN_CORRELATION_ID)));
6061
}
6162

6263
@Test
6364
public void addsGeneratedCorrelationIdToMDC() throws Exception {
6465

6566
new CorrelationIdFilter().doFilter(request, response, chain);
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67-
assertThat(mdcExtractor.getCorrelationId(), is(not(nullValue())));
68-
assertThat(mdcExtractor.getCorrelationId(), is(not(equalTo(KNOWN_CORRELATION_ID))));
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assertThat(getExtractedCorrelationId(), is(not(nullValue())));
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assertThat(getExtractedCorrelationId(), is(not(equalTo(KNOWN_CORRELATION_ID))));
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}
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7172
@Test
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105106
verify(response).getHeader(HttpHeaders.CORRELATION_ID.getName());
106107
verifyNoMoreInteractions(response);
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}
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109110
@Test
110111
public void usesCustomHeader() throws Exception {
111-
HttpHeader myHeader = new HttpHeader() {
112-
113-
@Override
114-
public boolean isPropagated() {
115-
return true;
116-
}
117-
118-
@Override
119-
public String getName() {
120-
return "my-header";
121-
}
122-
123-
@Override
124-
public String getFieldValue() {
125-
return null;
126-
}
127-
128-
@Override
129-
public String getField() {
130-
return "my-field";
131-
}
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133-
@Override
134-
public List<HttpHeader> getAliases() {
135-
return Collections.emptyList();
136-
}
137-
};
112+
HttpHeader myHeader = new HttpTestHeader("my-header", "my-field", null, false);
138113
when(request.getHeader("my-header")).thenReturn(KNOWN_CORRELATION_ID);
139-
CorrelationIdFromMDCExtractor myMdcExtractor = new CorrelationIdFromMDCExtractor("my-field");
140-
doAnswer(myMdcExtractor).when(chain).doFilter(request, response);
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142115
new CorrelationIdFilter(myHeader).doFilter(request, response, chain);
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144-
assertThat(myMdcExtractor.getCorrelationId(), is(equalTo(KNOWN_CORRELATION_ID)));
145-
verify(response).setHeader("my-header", KNOWN_CORRELATION_ID);
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}
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149-
private static class CorrelationIdFromMDCExtractor implements Answer<Void> {
150-
151-
private String correlationId;
152-
private String field;
153-
154-
private CorrelationIdFromMDCExtractor(String field) {
155-
this.field = field;
156-
}
157-
158-
public String getCorrelationId() {
159-
return correlationId;
160-
}
161-
162-
@Override
163-
public Void answer(InvocationOnMock invocation) throws Throwable {
164-
correlationId = MDC.get(field);
165-
return null;
166-
}
117+
assertThat(mdcExtractor.getField("my-field"), is(equalTo(KNOWN_CORRELATION_ID)));
118+
verify(response).setHeader("my-header", KNOWN_CORRELATION_ID);
167119
}
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169120
}

‎cf-java-logging-support-servlet/src/test/java/com/sap/hcp/cf/logging/servlet/filter/HttpTestHeader.java‎

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package com.sap.hcp.cf.logging.servlet.filter;
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import java.util.Arrays;
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import java.util.List;
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import com.sap.hcp.cf.logging.common.request.HttpHeader;
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8+
public class HttpTestHeader implements HttpHeader {
9+
10+
private String name;
11+
private String field;
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private String fieldValue;
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private boolean propagated;
14+
private List<HttpHeader> aliases;
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16+
public HttpTestHeader(String name, String field, String fieldValue, boolean propagated, HttpHeader... aliases) {
17+
this.name = name;
18+
this.field = field;
19+
this.fieldValue = fieldValue;
20+
this.propagated = propagated;
21+
this.aliases = Arrays.asList(aliases);
22+
}
23+
24+
@Override
25+
public boolean isPropagated() {
26+
return propagated;
27+
}
28+
29+
@Override
30+
public String getName() {
31+
return name;
32+
}
33+
34+
@Override
35+
public String getField() {
36+
return field;
37+
}
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39+
@Override
40+
public List<HttpHeader> getAliases() {
41+
return aliases;
42+
}
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44+
@Override
45+
public String getFieldValue() {
46+
return fieldValue;
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}
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}

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