Java学习总结--json

1.json的应用

json的应用比较广泛，比如javaweb前后台参数传递，移动应用参数传递等。

2.json与列表相互转化

需要jar包：

jackson-core-asl-1.9.2.jar

jackson-mapper-asl-1.9.2.jar

/**
* 装换为json格式字符串
* @param obj
* @return
*/
public static String toJson(Object obj) {
try {
return jsonMapper.writeValueAsString(obj);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
/**
* @param json:json数据格式的数组
* @param clazz：实体类
* @return
*/
@SuppressWarnings("unchecked")
public static List jsonToList(String json, Class<?> clazz){
try {
List list = new ArrayList();
List mapList = jsonMapper.readValue(json, List.class);
for (int i = 0; i < mapList.size(); i++) {
LinkedHashMap<String, Object> map = (LinkedHashMap<String, Object>) mapList.get(i);
Object obj = clazz.newInstance();
Field[] fileds = obj.getClass().getDeclaredFields();
for (Field field : fileds) {
String name = field.getName();
if(map.containsKey(name) && map.get(name)!= null){
//json会把原来的Date类型转换成时间戳，Float装换成Double
if(field.getType().equals(Date.class)){
Long l = (Long) map.get(name);
Date d = DateUtil.convertTimestampToDate(l);
RefUtils.invokeSetterMethod(obj, name, field.getType(),d);
}else if(field.getType().equals(Float.class)){
Double f = (Double)(Object)map.get(name);
RefUtils.invokeSetterMethod(obj, name, field.getType(), f.floatValue());
}else{
RefUtils.invokeSetterMethod(obj, name, field.getType(), map.get(name));
}
}
}
list.add(obj);
}
return list;
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

3.json工具类和测试类

测试类中简单引入jsonObject和jsonArray，因此需要额外的jar:

commons-beanutils-1.8.0.jar

commons-collections-3.2.jar

commons-lang-2.4.jar

commons-logging-1.2.jar

ezmorph-1.0.4.jar

json-lib-2.2.2-jdk15.jar

JsonUtil：json工具类

package com.sangbill.advanced.json;

import java.io.IOException;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Date;
import java.util.LinkedHashMap;
import java.util.List;

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

import com.sangbill.advanced.date.DateUtil;

public class JsonUtil {
private static  ObjectMapper jsonMapper = new ObjectMapper();
/**
* 装换为json格式字符串
* @param obj
* @return
*/
public static String toJson(Object obj) {
try {
return jsonMapper.writeValueAsString(obj);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
/**
* @param json:json数据格式的数组
* @param clazz：实体类
* @return
*/
@SuppressWarnings("unchecked")
public static List jsonToList(String json, Class<?> clazz){
try {
List list = new ArrayList();
List mapList = jsonMapper.readValue(json, List.class);
for (int i = 0; i < mapList.size(); i++) {
LinkedHashMap<String, Object> map = (LinkedHashMap<String, Object>) mapList.get(i);
Object obj = clazz.newInstance();
Field[] fileds = obj.getClass().getDeclaredFields();
for (Field field : fileds) {
String name = field.getName();
if(map.containsKey(name) && map.get(name)!= null){
//json会把原来的Date类型转换成时间戳，Float装换成Double
if(field.getType().equals(Date.class)){
Long l = (Long) map.get(name);
Date d = DateUtil.convertTimestampToDate(l);
RefUtils.invokeSetterMethod(obj, name, field.getType(),d);
}else if(field.getType().equals(Float.class)){
Double f = (Double)(Object)map.get(name);
RefUtils.invokeSetterMethod(obj, name, field.getType(), f.floatValue());
}else{
RefUtils.invokeSetterMethod(obj, name, field.getType(), map.get(name));
}
}
}
list.add(obj);
}
return list;
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}

RefUtils：反射工具类

package com.sangbill.advanced.json;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import com.sun.xml.internal.ws.util.StringUtils;

public abstract class RefUtils {
/**
* 调用Setter方法.
* @throws Exception
*/
public static Object invokeSetterMethod(Object obj, String propertyName,final Class<?> parameterTypes,Object value) throws Exception {
String setterMethodName = "set" + StringUtils.capitalize(propertyName);
return invokeMethod(obj, setterMethodName,new Class[]{parameterTypes}, new Object[] {value});
}
/**
* 调用Getter方法.
* @throws Exception
*/
public static Object invokeGetterMethod(Object obj, String propertyName) throws Exception {
String getterMethodName = "get" + StringUtils.capitalize(propertyName);
return invokeMethod(obj, getterMethodName, new Class[] {}, new Object[] {});
}

public static Object invokeMethod(final Object obj, final String methodName, final Class<?>[] parameterTypes,
final Object[] args) throws Exception {
Method method = getAccessibleMethod(obj, methodName, parameterTypes);
if (method == null) {
throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + obj + "]");
}

try {
return method.invoke(obj, args);
} catch (Exception e) {
throw convertReflectionExceptionToUnchecked(e);
}
}

public static RuntimeException convertReflectionExceptionToUnchecked(Exception e) {
if (e instanceof IllegalAccessException || e instanceof IllegalArgumentException
|| e instanceof NoSuchMethodException) {
return new IllegalArgumentException("Reflection Exception.", e);
} else if (e instanceof InvocationTargetException) {
return new RuntimeException("Reflection Exception.", ((InvocationTargetException) e).getTargetException());
} else if (e instanceof RuntimeException) {
return (RuntimeException) e;
}
return new RuntimeException("Unexpected Checked Exception.", e);
}

public static Method getAccessibleMethod(final Object obj, final String methodName,
final Class<?>... parameterTypes) {
//Assert.notNull(obj, "object不能为空");

for (Class<?> superClass = obj.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()) {
try {
Method method = superClass.getDeclaredMethod(methodName, parameterTypes);

method.setAccessible(true);

return method;

} catch (NoSuchMethodException e) {//NOSONAR
// Method不在当前类定义,继续向上转型
}
}
return null;
}
}

User：实体类

package com.sangbill.advanced.json;

import java.util.Date;

public class User {
private Long id;
private Integer age;
private Float count;
private Double point;
private Boolean isMember;
private String name;
private String passwd;
private Date birthday;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Float getCount() {
return count;
}
public void setCount(Float count) {
this.count = count;
}
public Double getPoint() {
return point;
}
public void setPoint(Double point) {
this.point = point;
}
public Boolean getIsMember() {
return isMember;
}
public void setIsMember(Boolean isMember) {
this.isMember = isMember;
}
public String getName() {
return name;
}
public vo
4000
id setName(String name) {
this.name = name;
}
public String getPasswd() {
return passwd;
}
public void setPasswd(String passwd) {
this.passwd = passwd;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}

}

Test：测试类

package com.sangbill.advanced.json;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Random;

import net.sf.json.JSONArray;
import net.sf.json.JSONObject;

public class Test {
public static void main(String[] args) {
int size = 10;
List<User> userList = getUserList(size);
String str = JsonUtil.toJson(userList);
System.out.println(str);
List list = JsonUtil.jsonToList(str,User.class);
print(null, list, null);
//jsonArray的装换
JSONArray arr = JSONArray.fromObject(str);
System.out.println(arr.size());
JSONObject obj =  (JSONObject) arr.get(0);
obj.get("id");
}

private static void print(String properties, List<User> userList,String order) {
System.out.println("order by "+properties+" "+order);
for (User user : userList) {
System.out.println(String.format("Id:%-20d ,age:%-2d, count:%-5f, point:%-5f, isMenber:%-5b, name:%-10s, passwd:%-10s",
user.getId(),user.getAge(),user.getCount(),user.getPoint(),user.getIsMember(),user.getName(),user.getPasswd()));
}
System.out.println("\n\n");
}
/**
* get random userList
* @param size
* @return
*/
private static List<User> getUserList(int size) {
List<User> userList = new ArrayList<User>();
for (int i = 0; i < size; i++) {
User u = getUser();
userList.add(u);
}
return userList;
}
/**
* get random user
* @return
*/
private static User getUser() {
User u = new User();
Random r = new Random();
boolean[] results = {true,false};
u.setId(r.nextLong());
u.setAge(r.nextInt(100));
u.setCount(r.nextFloat());
u.setPoint(r.nextDouble());
u.setIsMember(results[r.nextInt(2)]);
u.setName(getString());
u.setPasswd(getString());
u.setBirthday(new Date());
return u;
}
/**
* get random String
* @return
*/
private static String getString(){
String s = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
Random r = new Random();
int length = r.nextInt(10)+1;
int sLength = s.length();
StringBuffer sb = new StringBuffer();
for (int i = 0; i < length; i++) {
sb.append(s.charAt(r.nextInt(sLength)));
}
return sb.toString();
}
}