BAEL-4860: Java IllegalStateException: "getInputStream() has already been called for this request" (#14121)

* [BAEL-6203] Deserialize Generic Type with Jackson

* BAEL-4860: Java IllegalStateException: "getInputStream() has already been called for this request"

* BAEL-4860: Move code to new module spring-web-module/spring-mvc-java-3.

* BAEL-4860: update pom

* BAEL-4860: make the test methods public

spring-web-modules/pom.xml

@@ -28,6 +28,7 @@
         <module>spring-mvc-forms-thymeleaf</module>
         <module>spring-mvc-java</module>
         <module>spring-mvc-java-2</module>
+        <module>spring-mvc-java-3</module>
         <module>spring-mvc-velocity</module>
         <module>spring-mvc-views</module>
         <module>spring-mvc-webflow</module>

spring-web-modules/spring-mvc-java-3/README.md

@@ -0,0 +1 @@
+### Relevant Articles:

spring-web-modules/spring-mvc-java-3/pom.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>spring-mvc-java-3</artifactId>
+    <version>0.1-SNAPSHOT</version>
+    <name>spring-mvc-java-3</name>
+    <packaging>war</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-boot-2</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-boot-2</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>javax.servlet</groupId>
+            <artifactId>javax.servlet-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework</groupId>
+            <artifactId>spring-webmvc</artifactId>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>spring-mvc-java-3</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+</project>

spring-web-modules/spring-mvc-java-3/src/main/java/com/baeldung/filters/CacheRequestContentFilter.java

@@ -0,0 +1,23 @@
+package com.baeldung.filters;
+
+import org.springframework.web.util.ContentCachingRequestWrapper;
+
+import javax.servlet.*;
+import javax.servlet.annotation.WebFilter;
+import javax.servlet.http.HttpServletRequest;
+import java.io.IOException;
+
+@WebFilter(urlPatterns = "/*")
+public class CacheRequestContentFilter implements Filter {
+
+    @Override
+    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
+        if (request instanceof HttpServletRequest) {
+            String contentType = request.getContentType();
+            if (contentType == null || !contentType.contains("multipart/form-data")) {
+                request = new ContentCachingRequestWrapper((HttpServletRequest) request);
+            }
+        }
+        chain.doFilter(request, response);
+    }
+}

spring-web-modules/spring-mvc-java-3/src/test/java/com/baeldung/filters/HttpRequestUnitTest.java

@@ -0,0 +1,47 @@
+package com.baeldung.filters;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.mock.web.MockFilterChain;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.web.util.ContentCachingRequestWrapper;
+
+import javax.servlet.Filter;
+import javax.servlet.ServletException;
+import javax.servlet.ServletInputStream;
+import javax.servlet.ServletRequest;
+import javax.servlet.http.HttpServletRequest;
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class HttpRequestUnitTest {
+
+    @Test
+    public void givenHttpServletRequest_whenCalling_getReaderAfter_getInputStream_thenThrowIllegalStateException() throws IOException {
+        HttpServletRequest request = new MockHttpServletRequest();
+        try (ServletInputStream ignored = request.getInputStream()) {
+            IllegalStateException exception = assertThrows(IllegalStateException.class, request::getReader);
+            assertEquals("Cannot call getReader() after getInputStream() has already been called for the current request",
+                    exception.getMessage());
+        }
+    }
+
+    @Test
+    public void givenServletRequest_whenDoFilter_thenCanCallBoth() throws ServletException, IOException {
+        MockHttpServletRequest req = new MockHttpServletRequest();
+        MockHttpServletResponse res = new MockHttpServletResponse();
+        MockFilterChain chain = new MockFilterChain();
+
+        Filter filter = new CacheRequestContentFilter();
+        filter.doFilter(req, res, chain);
+
+        ServletRequest request = chain.getRequest();
+        assertTrue(request instanceof ContentCachingRequestWrapper);
+
+        // now we can call both getInputStream() and getReader()
+        request.getInputStream();
+        request.getReader();
+    }
+
+}