本文介紹了找不到媒體type=application/xml、type=class java.util.HashMap$Values的MessageBodyWriter的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！
問題描述
我的API方法無法將對象轉換為XML，但它可以轉換為JSON。當方法返回類型為Collection(Map)時，它轉換為XML，沒有任何運行時異常(找不到MessageBodyWriter)，但是當使用Response作為返回類型時，它會導致運行時異常。我在這里提到代碼。我認為我的代碼中沒有任何問題，只是依賴項有問題。
package lk.ac.jfn.vau.MyDBapi.Model;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class Department {
private long Id;
private String Name;
private String Location;
public Department() {
}
public Department(long id, String name, String location) {
super();
Id = id;
Name = name;
Location = location;
}
public long getId() {
return Id;
}
public void setId(long id) {
Id = id;
}
public String getName() {
return Name;
}
public void setName(String name) {
Name = name;
}
public String getLocation() {
return Location;
}
public void setLocation(String location) {
Location = location;
}
}
package lk.ac.jfn.vau.MyDBapi.Repo;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class Repo {
private static final String DB_Driver = "com.mysql.jdbc.Driver";
private static final String DB_Connection = "jdbc:mysql://localhost:3306/";
private static final String DB_Name = "departmentapi";
private static final String DB_User = "root";
private static final String DB_Password = "";
public static void getDriver() {
try {
Class.forName(DB_Driver);
System.out.println("Driver found");
} catch (ClassNotFoundException e) {
System.out.println("Driver not found " + e.getMessage());
}
}
public static Connection getConnection() {
Connection connection = null;
try {
connection = DriverManager.getConnection(DB_Connection + DB_Name, DB_User, DB_Password);
System.out.println("Database Connected");
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return connection;
}
public ResultSet get(String query, Connection connection) {
ResultSet resultSet = null;
try {
Statement statement = connection.createStatement();
resultSet = statement.executeQuery(query);
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return resultSet;
}
}
package lk.ac.jfn.vau.MyDBapi.Repo;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import lk.ac.jfn.vau.MyDBapi.Model.Department;
public class DepartmentRepo extends Repo {
Connection connection=null;
public DepartmentRepo() {
getDriver();
connection = getConnection();
}
Map<Long, Department>map=new HashMap<Long, Department>();
public Collection<Department> getAll(){
ResultSet resultSet=get("select * from department", connection);
try {
while(resultSet.next()) {
Department department=new Department(resultSet.getLong(1), resultSet.getString(2), resultSet.getString(3));
map.put(department.getId(), department);
}
} catch (SQLException e) {
System.out.println(e.getMessage());
}
return map.values();
}
}
package lk.ac.jfn.vau.MyDBapi;
import java.util.Collection;
import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.Response.Status;
import lk.ac.jfn.vau.MyDBapi.Model.Department;
import lk.ac.jfn.vau.MyDBapi.Repo.DepartmentRepo;
@Path("/dept")
@Produces(value = {MediaType.APPLICATION_JSON,MediaType.APPLICATION_XML})
@Consumes(MediaType.APPLICATION_JSON)
public class DepartmentResource {
private DepartmentRepo repo=new DepartmentRepo();
@GET
public Response getDepartments() {
Collection<Department> departments = repo.getAll();
if(!departments.isEmpty()) {
return Response.status(Status.FOUND).entity(departments).build();
}
return Response.status(Status.NOT_FOUND).entity("Nothing Found").build();
}
}
POM.xml
<dependencies>
<dependency>
<groupId>org.glassfish.jersey.containers</groupId>
<artifactId>jersey-container-servlet-core</artifactId>
<!-- use the following artifactId if you don't need servlet 2.x compatibility -->
<!-- artifactId>jersey-container-servlet</artifactId -->
</dependency>
<dependency>
<groupId>org.glassfish.jersey.media</groupId>
<artifactId>jersey-media-json-jackson</artifactId>
</dependency>
<dependency>
<groupId>org.glassfish.jaxb</groupId>
<artifactId>jaxb-runtime</artifactId>
<version>2.3.2</version>
</dependency>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.34</version>
</dependency>
</dependencies>
推薦答案
對于JAXB(XML提供程序)，您需要使用GenericEntity。
GenericEntity<Collection<Department>> entity
= new GenericEntity<Collection<Department>>(departments){};
return Response.ok(entity).build();
您需要這樣做的原因是JAXB需要知道類型信息才能序列化。當您只返回泛型實體時，而不是Response，泛型類型信息在方法簽名中
@GET
public Collection<Department> getDepartments() {}
使用Response時，由于類型擦除，常規信息不可用。所以JAX-RS允許使用GenericEntity。但是您不能只使用實例，因為類型擦除不允許這樣做。您實際上需要使用匿名類
new GenericEntity<Collection<Department>>(departments){}
注意末尾的花括號。這是一個匿名類。通過反射，您可以從此匿名類獲取泛型類型參數。
這篇關于找不到媒體type=application/xml、type=class java.util.HashMap$Values的MessageBodyWriter的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，
