关于json：将Map 转换为POJO

Convert a Map to a POJO

我一直在查看Jackson，但似乎我必须将Map转换为JSON，然后将所得的JSON转换为POJO。

有没有一种方法可以将Map直接转换为POJO？

好吧，您也可以使用Jackson来实现。 (由于您正在考虑使用杰克逊，因此似乎更舒适)。

使用ObjectMapper的convertValue方法：

1 2	final ObjectMapper mapper = new ObjectMapper(); // jackson's objectmapper final MyPojo pojo = mapper.convertValue(map, MyPojo.class);

无需转换为JSON字符串或其他内容；直接转换的速度要快得多。

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Gson的解决方案：

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Gson gson = new Gson();
JsonElement jsonElement = gson.toJsonTree(map);
MyPojo pojo = gson.fromJson(jsonElement, MyPojo.class);

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是的，绝对有可能避免中间转换为JSON。使用类似Dozer的深度复制工具，您可以将地图直接转换为POJO。这是一个简单的例子：

示例POJO：

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public class MyPojo implements Serializable {
private static final long serialVersionUID = 1L;

private String id;
private String name;
private Integer age;
private Double savings;

public MyPojo() {
super();
}

// Getters/setters

@Override
public String toString() {
return String.format(
"MyPojo[id = %s, name = %s, age = %s, savings = %s]", getId(),
getName(), getAge(), getSavings());
}
}

转换代码示例：

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public class CopyTest {
@Test
public void testCopyMapToPOJO() throws Exception {
final Map<String, String> map = new HashMap<String, String>(4);
map.put("id","5");
map.put("name","Bob");
map.put("age","23");
map.put("savings","2500.39");
map.put("extra","foo");

final DozerBeanMapper mapper = new DozerBeanMapper();
final MyPojo pojo = mapper.map(map, MyPojo.class);
System.out.println(pojo);
}
}

输出：

MyPojo[id = 5, name = Bob, age = 23, savings = 2500.39]

注意：如果将源映射更改为Map，则可以在任意深度嵌套的属性上进行复制(使用Map只能获得一个级别)。

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如果您的班级中有通用类型，则应将TypeReference与convertValue()一起使用。

1 2	final ObjectMapper mapper = new ObjectMapper(); final MyPojo<MyGenericType> pojo = mapper.convertValue(map, new TypeReference<MyPojo<MyGenericType>>() {});

您也可以使用它将pojo转换回java.util.Map。

1 2	final ObjectMapper mapper = new ObjectMapper(); final Map<String, Object> map = mapper.convertValue(pojo, new TypeReference<Map<String, Object>>() {});

我测试了Jackson和BeanUtils，发现BeanUtils更快。
在我的机器上(Windows8.1，JDK1.7)我得到了这个结果。

1 2	BeanUtils t2-t1 = 286 Jackson t2-t1 = 2203

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public class MainMapToPOJO {

public static final int LOOP_MAX_COUNT = 1000;

public static void main(String[] args) {
Map<String, Object> map = new HashMap<>();
map.put("success", true);
map.put("data","testString");

runBeanUtilsPopulate(map);

runJacksonMapper(map);
}

private static void runBeanUtilsPopulate(Map<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < LOOP_MAX_COUNT; i++) {
try {
TestClass bean = new TestClass();
BeanUtils.populate(bean, map);
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
long t2 = System.currentTimeMillis();
System.out.println("BeanUtils t2-t1 =" + String.valueOf(t2 - t1));
}

private static void runJacksonMapper(Map<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < LOOP_MAX_COUNT; i++) {
ObjectMapper mapper = new ObjectMapper();
TestClass testClass = mapper.convertValue(map, TestClass.class);
}
long t2 = System.currentTimeMillis();
System.out.println("Jackson t2-t1 =" + String.valueOf(t2 - t1));
}}

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哈密??兹
如果使用许多数据，请使用Jackson进行转换
轻量数据，使用Apache ...
测试用例：

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<wyn>
</p>

import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.beanutils.BeanUtils;

import com.fasterxml.jackson.databind.ObjectMapper;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

public class TestPerf {

public static final int LOOP_MAX_COUNT = 1000;

public static void main(String[] args) {
Map<String, Object> map = new HashMap<>();
map.put("success", true);
map.put("number", 1000);
map.put("longer", 1000L);
map.put("doubler", 1000D);
map.put("data1","testString");
map.put("data2","testString");
map.put("data3","testString");
map.put("data4","testString");
map.put("data5","testString");
map.put("data6","testString");
map.put("data7","testString");
map.put("data8","testString");
map.put("data9","testString");
map.put("data10","testString");

runBeanUtilsPopulate(map);

runJacksonMapper(map);
}

private static void runBeanUtilsPopulate(Map<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < LOOP_MAX_COUNT; i++) {
try {
TestClass bean = new TestClass();
BeanUtils.populate(bean, map);
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
long t2 = System.currentTimeMillis();
System.out.println("BeanUtils t2-t1 =" + String.valueOf(t2 - t1));
}

private static void runJacksonMapper(Map<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < LOOP_MAX_COUNT; i++) {
ObjectMapper mapper = new ObjectMapper();
TestClass testClass = mapper.convertValue(map, TestClass.class);
}
long t2 = System.currentTimeMillis();
System.out.println("Jackson t2-t1 =" + String.valueOf(t2 - t1));
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public static class TestClass {
private Boolean success;
private Integer number;
private Long longer;
private Double doubler;
private String data1;
private String data2;
private String data3;
private String data4;
private String data5;
private String data6;
private String data7;
private String data8;
private String data9;
private String data10;

}
}

convert Map to POJO example.Notice the Map key contains underline and field variable is hump.

用户类POJO

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import com.fasterxml.jackson.annotation.JsonProperty;
import lombok.Data;

@Data
public class User {
@JsonProperty("user_name")
private String userName;
@JsonProperty("pass_word")
private String passWord;
}

App.class测试示例

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import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;

public class App {
public static void main(String[] args) {
Map<String, String> info = new HashMap<>();
info.put("user_name","Q10Viking");
info.put("pass_word","123456");

ObjectMapper mapper = new ObjectMapper();
User user = mapper.convertValue(info, User.class);

System.out.println("-------------------------------");
System.out.println(user);
}
}
/**output
-------------------------------
User(userName=Q10Viking, passWord=123456)
*/