使用Spring MVC for REST时,如何让Jackson能够打印出漂亮的JSON？

Question

在使用Spring MVC开发REST服务的同时,我希望在开发中渲染JSON"漂亮打印",但在生产中正常(减少空白).

Answer 1

如果您使用的是Spring Boot 1.2或更高版本,那么简单的解决方案就是添加

spring.jackson.serialization.INDENT_OUTPUT=true

到application.properties文件.这假设您使用Jackson进行序列化.

如果您使用的是早期版本的Spring Boot,则可以添加

http.mappers.json-pretty-print=true

此解决方案仍适用于Spring Boot 1.2,但已弃用,最终将完全删除.您将在启动时在日志中收到弃用警告.

(测试使用spring-boot-starter-web)

Answer 2

当我发布这个问题时,我得到了一个答案,但我认为无论如何我都会发布它,以防有更好的替代解决方案.这是我的经历:

首先是第一件事.该MappingJacksonHttpMessageConverter希望你注入杰克逊ObjectMapper实例,该实例执行杰克逊的配置(而不是通过Spring类).

我认为这样做会很容易:

创建一个ObjectMapperFactoryBean允许我自定义ObjectMapper可以注入的实例的实现MappingJacksonHttpMessageConverter.例如:

<bean id="jacksonHttpMessageConverter" class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
    <property name="objectMapper">
        <bean class="com.foo.my.ObjectMapperFactoryBean">
            <property name="prettyPrint" value="${json.prettyPrint}"/>
        </bean>
    </property>
</bean>

然后,在我的ObjectMapperFactoryBean实现中,我可以做到这一点(正如在SO上的其他地方记录的那样):

ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationConfig.Feature.INDENT_OUTPUT, isPrettyPrint());
return mapper;

但它没有用.并试图弄清楚为什么是一场噩梦.杰克逊出局是对耐心的一次重大考验.查看它的源代码只会让你更加困惑,因为它使用过时和钝的配置形式(用于打开/关闭功能的整数位掩码？你在开玩笑吗？)

我基本上不得不MappingJacksonHttpMessageConverter从头开始重写Spring ,并将其writeInternal实现覆盖如下:

@Override
protected void writeInternal(Object o, HttpOutputMessage outputMessage)
        throws IOException, HttpMessageNotWritableException {

    JsonEncoding encoding = getEncoding(outputMessage.getHeaders().getContentType());
    JsonGenerator jsonGenerator =
            getObjectMapper().getJsonFactory().createJsonGenerator(outputMessage.getBody(), encoding);
    try {
        if (this.prefixJson) {
            jsonGenerator.writeRaw("{} && ");
        }
        if (isPrettyPrint()) {
            jsonGenerator.useDefaultPrettyPrinter();
        }
        getObjectMapper().writeValue(jsonGenerator, o);
    }
    catch (JsonGenerationException ex) {
        throw new HttpMessageNotWritableException("Could not write JSON: " + ex.getMessage(), ex);
    }
}

我在现有实现中添加的唯一内容是以下块:

if (isPrettyPrint()) {
    jsonGenerator.useDefaultPrettyPrinter();
}

isPrettyPrint()是一个JavaBeans兼容的getter w /匹配setter,我添加到我的MappingJacksonHttpMessageConverter子类.

只有在跳过这些箍之后我才能根据我的${json.prettyPrint}值打开或关闭漂亮的打印(根据应用程序的部署方式设置为属性).

我希望将来可以帮助别人!

Answer 3

当您使用Jackson 2.0.0时,您可以按照Les想要的方式进行操作.我目前使用RC3,配置似乎按预期工作.

ObjectMapper jacksonMapper = new ObjectMapper();
jacksonMapper.configure(SerializationFeature.INDENT_OUTPUT, true);

转换

{"foo":"foo","bar":{"field1":"field1","field2":"field2"}}

成

{
  "foo" : "foo",
  "bar" : {
    "field1" : "field1",
    "field2" : "field2"
  }
}

Answer 4

可能我建议这种方法,它适用于Spring 4.0.x和可能的旧版本.

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import java.util.List;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
@EnableWebMvc    
public class WebMvcConfig extends WebMvcConfigurerAdapter {


    @Bean
    public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessageConverter();
        mappingJackson2HttpMessageConverter.setObjectMapper(objectMapper());
        return mappingJackson2HttpMessageConverter;
    }

    @Bean
    public ObjectMapper objectMapper() {
        ObjectMapper objMapper = new ObjectMapper();
        objMapper.enable(SerializationFeature.INDENT_OUTPUT);
        return objMapper;
    }

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        super.configureMessageConverters(converters);        
        converters.add(mappingJackson2HttpMessageConverter());
    }

}

感谢Willie Wheeler提供的解决方案:Willie Wheeler的Spring博客

Answer 5

如何让杰克逊打印出它生成的JSON内容呢？

这是一个简单的例子:

原始JSON输入:

{"one":"AAA","two":["BBB","CCC"],"three":{"four":"DDD","five":["EEE","FFF"]}}

Foo.java:

import java.io.FileReader;

import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ObjectWriter;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    ObjectMapper mapper = new ObjectMapper();
    MyClass myObject = mapper.readValue(new FileReader("input.json"), MyClass.class);
    // this is Jackson 1.x API only: 
    ObjectWriter writer = mapper.defaultPrettyPrintingWriter();
    // ***IMPORTANT!!!*** for Jackson 2.x use the line below instead of the one above: 
    // ObjectWriter writer = mapper.writer().withDefaultPrettyPrinter();
    System.out.println(writer.writeValueAsString(myObject));
  }
}

class MyClass
{
  String one;
  String[] two;
  MyOtherClass three;

  public String getOne() {return one;}
  void setOne(String one) {this.one = one;}
  public String[] getTwo() {return two;}
  void setTwo(String[] two) {this.two = two;}
  public MyOtherClass getThree() {return three;}
  void setThree(MyOtherClass three) {this.three = three;}
}

class MyOtherClass
{
  String four;
  String[] five;

  public String getFour() {return four;}
  void setFour(String four) {this.four = four;}
  public String[] getFive() {return five;}
  void setFive(String[] five) {this.five = five;}
}

输出:

{
  "one" : "AAA",
  "two" : [ "BBB", "CCC" ],
  "three" : {
    "four" : "DDD",
    "five" : [ "EEE", "FFF" ]
  }
}

如果这种方法不能完全满足您的需求,那么如果您在API文档v1.8.1中搜索"漂亮",它将会显示相关的可用组件.如果您使用API​​版本2.x,那么请查看较新的API 2.1.0文档.

Answer 6

通过添加和配置MappingJackson2HttpMessageConverter转换器将启用Pretty print .在生产环境中禁用prettyprint.

消息转换器配置

<mvc:annotation-driven>
    <mvc:message-converters>
        <bean id="jacksonHttpMessageConverter"
            class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
            <property name="prettyPrint" value="${json.prettyPrint}" />
        </bean>
    </mvc:message-converters>
</mvc:annotation-driven>