创建自定义异常

要处理基于 JAX-RS 的 Web 服务中的自定义异常，我们应该创建一个异常类，然后实现 ExceptionMapper接口。

package com.onitroad.jersey;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;
@Provider
public class MissingFileException extends Exception implements
				ExceptionMapper<MissingFileException> 
{
	private static final long serialVersionUID = 1L;
	public MissingFileException() {
		super("No File found with given name !!");
	}
	public MissingFileException(String string) {
		super(string);
	}
	@Override
	public Response toResponse(MissingFileException exception) 
	{
		return Response.status(404).entity(exception.getMessage())
									.type("text/plain").build();
	}
}

如何从 REST API 抛出异常

现在，当在所需位置找不到用户请求的文件时，我们可以抛出“MissingFileException”。

package com.onitroad.jersey;
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.StreamingOutput;
@Path("/download")
public class JerseyService 
{
	@GET
	@Path("/{fileName}")
	public Response downloadPdfFile(final @PathParam("fileName") String fileName) throws MissingFileException
	{
		final String fullFilePath = "C:/temp/" + fileName;

		File file = new File(fullFilePath);

		if(file.exists() == false){
			throw new MissingFileException(fileName + " does not existing on this server !!");
		}

		StreamingOutput fileStream =  new StreamingOutput()
		{
			@Override
			public void write(java.io.OutputStream output) throws IOException
			{
				try 
				{
					java.nio.file.Path path = Paths.get(fullFilePath);
					byte[] data = Files.readAllBytes(path);
					output.write(data);
					output.flush();
				} 
				catch (IOException e) 
				{
					throw new IOException("Error while reading file :: '"+fileName+"' !!");
				}
			}
		};
		return Response
	            .ok(fileStream, MediaType.APPLICATION_OCTET_STREAM)
	            .header("content-disposition","attachment; filename = '"+fileName)
	            .build();
	}
}

Jersey 异常处理示例

现在是测试 jersey 异常映射器的时候了。

请求存在的文件

将返回200状态，没有异常

请求不存在的文件

将返回404错误

未捕获的异常处理

如果我们想在进入用户屏幕之前处理所有未捕获的异常，则必须映射 Throwable本身。

package com.onitroad.jersey.provider;
import javax.ws.rs.core.Response;
import javax.ws.rs.ext.ExceptionMapper;
import javax.ws.rs.ext.Provider;
@Provider
public class UncaughtException extends Throwable implements ExceptionMapper<Throwable>
{
    private static final long serialVersionUID = 1L;

    @Override
    public Response toResponse(Throwable exception)
    {
        return Response.status(500).entity("Something bad happened. Please try again !!").type("text/plain").build();
    }
}