在將物件轉為json或xml格式時,可能會因為key欄位名稱有特殊字元,而無法產生出正常的輸出。舉例來說:
@JsonProperty(value="metadata") private Map<String, Object> mMetadata;mMetadata為map物件,如果key的內容包含特殊字元,如$ARG$,產生出的xml則會變成不合法格式:
<Command xmlns=""><metadata><$ARG$>123</$ARG$></metadata></Command>接下來看看如何解決這問題。
我想到的幾個解法是:
在這我使用了第三個解法,並針對要處理的項目:
Command類別是此範例中,要轉為json與xml格式的目標:
import java.util.Map; import com.fasterxml.jackson.annotation.JsonProperty; import com.fasterxml.jackson.databind.annotation.JsonSerialize; public class Command { @JsonProperty(value="name") private String mName; @JsonSerialize(keyUsing=KeySerializer.class) @JsonProperty(value="metadata") private Map<String, Object> mMetadata; public Command() { } public void setMetadata(Map<String, Object> aMetadata){ mMetadata = aMetadata; } public String getName() { return mName; } public void setName(String aName) { this.mName = aName; } }對於mMetadata,我使用了@JsonSerialize(keyUsing=KeySerializer.class),要透過KeySerializer將key濾掉$字號。
從annotation的宣告可得知,自訂的Serializer必須繼承於JsonSerializer:
public Class<? extends JsonSerializer> keyUsing() default JsonSerializer.None.class;來看看我做的KeySerializer,針對key value將$取代為空白:
import java.io.IOException; import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; public class KeySerializer extends JsonSerializer<String> { @Override public void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException, JsonProcessingException { gen.writeFieldName(value.replaceAll("\\$", "")); } }接下來看看產生的結果。
@Test public void testJsonGenerator() throws IOException { ObjectMapper mapper = new ObjectMapper(); JsonGenerator generator = mapper.getFactory().createGenerator(System.out); Map<String, Object> metadata = new HashMap<String, Object>(); Map<String, Object> tmp = new HashMap<String, Object>(); tmp.put("$ARG4$", "789"); tmp.put("$ARG5$", "111"); metadata.put("$ARG1$", "123"); metadata.put("$ARG2$", "456"); metadata.put("$ARG3$", tmp); Command cmd = new Command(); cmd.setName("ping"); cmd.setMetadata(metadata); generator.writeObject(cmd); }Output:
{"name":"ping","metadata":{"ARG3":{"ARG5":"111","ARG4":"789"},"ARG2":"456","ARG1":"123"}}
@Test public void testXmlGenerator() throws IOException { XmlMapper mapper = new XmlMapper(); JsonGenerator generator = mapper.getFactory().createGenerator(System.out); Map<String, Object> metadata = new HashMap<String, Object>(); Map<String, Object> tmp = new HashMap<String, Object>(); tmp.put("$ARG4$", "789"); tmp.put("$ARG5$", "111"); metadata.put("$ARG1$", "123"); metadata.put("$ARG2$", "456"); metadata.put("$ARG3$", tmp); Command cmd = new Command(); cmd.setName("ping"); cmd.setMetadata(metadata); generator.writeObject(cmd); }Output:
<Command xmlns=""><name>ping</name><metadata><ARG3><ARG5>111</ARG5><ARG4>789</ARG4></ARG3><ARG2>456</ARG2><ARG1>123</ARG1></metadata></Command>