解析JSON对象时NoClassDefFoundError JsonAutoDetect

Question

我正在使用Amazon的云服务开发一个webapp，我需要使用JSON对象。我的项目是如何设置的，我有一个HTML表单，用户将在其中填写信息并提交。一旦提交，数据将被放入在线数据库，并向他们发送确认电子邮件。在将数据提交到数据库之前，我需要将所有数据放入JSON对象中。我的servlet是用Java完成的，如下所示：

public class FormHandling extends HttpServlet {
    //doGet function
    public void doGet (HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        // In this part of the code I take in the user data and build an HTML
        // page and return it to the user

        // Create String Mapping for User Data object
        Map<String,Object> userData = new HashMap<String,Object>();

        // Map the names into one struct. In the code below we are creating 
        // values for the nameStruct from the information the user has
        // submitted on the form.
        Map<String,String> nameStruct = new HashMap<String,String>();
        nameStruct.put("fName", request.getParameter("fname"));
        nameStruct.put("lName", request.getParameter("lname"));
        nameStruct.put("mInit", request.getParameter("minit"));

        // Map the three email's together (providing there are 3).
        // This is the same logic as the names.
        Map<String,String> emailStruct = new HashMap<String,String>();
        emailStruct.put("email", request.getParameter("email1"));
        emailStruct.put("email", request.getParameter("email2"));
        emailStruct.put("email", request.getParameter("email3"));

        // Put Name Hash Value Pair inside User Data Object
        userData.put("name", nameStruct);
        userData.put("emails", emailStruct);
        userData.put("age", 22);

        // Create the Json data from the userData
        createJson(userData);

        // Close writer
        out.close();
    }

    public File createJson(Map<String,Object> userData) 
        throws JsonGenerationException, JsonMappingException, IOException {
        File user = new File("user.json");

        // Create mapper object
        ObjectMapper mapper = new ObjectMapper();

        // Add the userData information to the json file
        html" target="_blank">mapper.writeValue(user, userData);
        return user;
    }
}

使用此代码提交表单时，会收到以下错误消息：

java.lang.NoClassDefFoundError： com/Fast erxml/jackson/注释/JsonAutoDetectcom.fasterxml.jackson.databind.introspect.VisibilityChecker$Std.（VisibilityChecker.java:169）com.fasterxml.jackson.databind.ObjectMapper.（ObjectMapper.java:197）edu.tcnj.FormHandling.createJson（FormHandling.java:115）edu.tcnj.FormHandling.do获取（FormHandling.java:104）edu.tcnj.FormHandling.doPost（FormHandling.java:131）javax.servlet.http.HttpServlet.service（HttpServlet.java:641）javax.servlet.http.HttpServlet.service（HttpServlet.java:722）

现在我知道那个错误意味着它没有找到Jackson数据库库。我正在Eclipse中开发，我知道构建路径不时会出错，所以我也将库放在WebContent\WEB-INF\lib文件夹中。这解决了我以前遇到过的问题。但是，这似乎并没有解决我这次的问题。我甚至打开了jar文件来物理检查所需的库和类是否在那里，而且它们在那里。我尝试了四处搜索并寻找不同的方法来包含库，但似乎没有任何效果。

Answer 1

或以下渐变配置：

compile 'com.fasterxml.jackson.core:jackson-core:2.2.2'
compile 'com.fasterxml.jackson.core:jackson-databind:2.2.2'
compile 'com.fasterxml.jackson.core:jackson-annotations:2.2.2'

Answer 2

为maven用户扩展@jeffamaphone的精彩回答

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.7.3</version>
</dependency>

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.7.3</version>
</dependency>

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.7.3</version>
</dependency>

Answer 3

对于将来来到这里的人，答案是：

如果您只复制了jackson core和jackson databind，则需要jackson注解才能使用ObjectMapper。

例如，确保你有这样的东西：

[16:32:01]:/android-project/libs     master]$ ls -lAF
total 2112
-rw-r--r--@ 1 jeffamaphone  staff   33525 Jun 18 16:06 jackson-annotations-2.0.2.jar
-rw-r--r--@ 1 jeffamaphone  staff  193693 Jun  7 16:42 jackson-core-2.0.2.jar
-rw-r--r--@ 1 jeffamaphone  staff  847121 Jun 18 15:22 jackson-databind-2.0.2.jar